Numerics

1X

First phase of third-generation (3G) mobile wireless technology for CDMA2000 networks.

1XEV

Evolutionary phase of third-generation (3G) CDMA2000 networks, divided into two phases: 1XEV-DO (data only) and 1XEV-DV (data and voice).

3DES

Triple Data Encryption Standard. A 168-bit encryption algorithm that encrypts data blocks with three different keys in succession, achieving a higher level of encryption than standard DES. 3DES is often implemented with cipher block chaining (CBC). 3DES is one of the strongest encryption algorithms available for use in virtual private networks (VPNs). Also called triple DES.

3GPP

Third-generation Partnership Project. Created to expedite the development of open, globally accepted technical specifications for the Universal Mobile Telecommunications System (UMTS).

802.1ad

The IEEE specification for “Q-in-Q” encapsulation and bridging of Ethernet frames.

802.1ah

The IEEE specification for media access control (MAC) tunneling encapsulation and bridging of Ethernet frames across a provided backbone-managed bridge.

802.1Q

The IEEE specification for adding virtual local area network (VLAN) tags to an Ethernet frame.

802.3ah

The IEEE specification defining Ethernet between the subscriber and the immediate service provider. Also known as Ethernet in the first or last mile.

A

AAL

ATM adaptation layer. A series of protocols enabling various types of traffic, including voice, data, image, and video, to run over an ATM network.

AAL5 mode

ATM adaption layer 5. One of four AALs recommended by the ITU-T. AAL5 is used predominantly for the transfer of classical IP over ATM. AAL5 is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability. It is a Layer 2 circuit transport mode that allows you to send ATM cells between ATM2 IQ interfaces across a Layer 2 circuit-enabled network. You use Layer 2 circuit AAL5 transport mode to tunnel a stream of AAL5-encoded ATM segmentation and reassembly protocol data units (SAR-PDUs) over an MPLS or IP backbone. See also cell-relay mode, Layer 2 circuits, standard AAL5 mode, trunk mode.

ABR

Area border router. Router that belongs to more than one area. Used in OSPF. See also OSPF.

access concentrator

Router that acts as a server in a Point-to-Point Protocol over Ethernet (PPPoE) session, for example, an E-series router.

accounting services

Method of collecting network data related to resource usage.

acess point name

See also APN.

ACFC

Address and Control Field Compression. Enables routers to transmit packets without the two 1-byte address and control fields (0xff and 0x03) normal for PPP-encapsulated packets, thus transmitting less data and conserving bandwidth. ACFC is defined in RFC 1661, The Point-to-Point Protocol (PPP). See also PFC.

active route

Route chosen from all routes in the routing table to reach a destination. Active routes are installed into the forwarding table.

adaptive services

Set of services or applications that you can configure on an Adaptive Services PIC (AS PIC). The services and applications include stateful firewall, Network Address Translation (NAT), intrusion detection service (IDS), Internet Protocol Security (IPsec), Layer 2 Tunneling Protocol (L2TP), and voice services. See also tunneling protocol.

add/drop multiplexer

See ADM.

Address and Control Field Compression

See ACFC.

address match conditions

Use of an IP address as a match criterion in a routing policy or a firewall filter.

Address Resolution Protocol

See ARP.

adjacency

Portion of the local routing information that pertains to the reachability of a single neighbor over a single circuit or interface.

Adjacency-RIB-In

Logical software table that contains BGP routes received from a specific neighbor.

Adjacency-RIB-Out

Logical software table that contains BGP routes to be sent to a specific neighbor.

ADM

Add/drop multiplexer. SONET functionality that allows lower-level signals to be dropped from a high-speed optical connection.

ADSL

Asymmetrical digital subscriber line. A technology that allows more data to be sent over existing copper telephone lines, using the public switched telephone network (PSTN). ADSL supports data rates from 1.5 to 9 Mbps when receiving data (downstream rate) and from 16 to 640 Kbps when sending data (upstream rate).

ADSL2+ interface

ADSL interface that supports ITU-T Standard G.992.5. ADSL2+ allocates downstream (provider-to-customer) data rates of up to 25 Mbps and upstream (customer-to-provider) rates of up to 1 Mbps.

ADSL2 interface

ADSL interface that supports ITU-T Standard G.992.3 and ITU-T Standard G.992.4. ADSL2 allocates downstream (provider-to-customer) data rates of up to 12 Mbps and upstream (customer-to-provider) rates of up to 1 Mbps.

ADSL Annex A PIM

See ITU-T Rec. G.992.1.

ADSL Annex B PIM

See ITU-T Rec. G.992.1.

ADSL interface

Asymmetrical digital subscriber line interface. Physical WAN interface that connects a router to a digital subscriber line access multiplexer (DSLAM). An ADSL interface allocates line bandwidth asymmetrically. Downstream (provider-to-customer) data rates can be up to 8 Mbps for ADSL, 12 Mbps for ADSL2, and 25 Mbps for ADSL2+. Upstream (customer-to-provider) rates can be up to 800 Kbps for ADSL and 1 Mbps for ADSL2 and ADSL2+, depending on the implementation.

Advanced Encryption Standard

See AES.

AES

Advanced Encryption Standard. Defined in FIPS PUB 197. The AES algorithm uses keys of 128, 192, or 256 bits to encrypt and decrypt data in blocks of 128 bits.

aggregated interface

Logical bundle of physical interfaces. The aggregated interface is managed as a single interface with one IP address. Network traffic is dynamically distributed across ports, so administration of data flowing across a given port is done automatically within the aggregated link. Using multiple ports in parallel provides redundancy and increases the link speed beyond the limits of any single port.

aggregate route

Combination of groups of routes that have common addresses into a single entry in a routing table.

AH

Authentication header. A component of the IPsec protocol used to verify that the contents of a packet have not changed, and to validate the identity of the sender. See also ESP.

ALI

ATM line interface. Interface between ATM and 3G systems. See also ATM.

alternate priority queuing

See APQ.

ANSI

American National Standards Institute. The United States’ representative to the ISO.

Any Source Multicast

See ASM.

APN

Access point name. When mobile stations connect to IP networks over a wireless network, the GGSN uses the APN to distinguish among the connected IP networks (known as APN networks). In addition to identifying these connected networks, an APN is also a configured entity that hosts the wireless sessions, which are called Packet Data Protocol (PDP) contexts.

application-specific integrated circuit

See ASIC.

APQ

Alternate priority queuing. Dequeuing method that has a special queue, similar to strict-priority queuing (SPQ), which is visited only 50 percent of the time. The packets in the special queue still have a predictable latency, although the upper limit of the delay is higher than that with SPQ. Since the other configured queues share the remaining 50 percent of the service time, queue starvation is usually avoided. See also SPQ.

APS

Automatic Protection Switching. Technology used by SONET ADMs to protect against circuit faults between the ADM and a router and to protect against failing routers.

area

Routing subdomain that maintains detailed routing information about its own internal composition as well as routing information that allows it to reach other routing subdomains. In IS-IS, an area corresponds to a Level 1 subdomain.

In IS-IS and OSPF, a set of contiguous networks and hosts within an autonomous system that have been administratively grouped together.

area border router

See ABR.

ARP

Address Resolution Protocol. Protocol used for mapping IPv4 addresses to media access control (MAC) addresses. See also NDP.

AS

Autonomous system. Set of routers under a single technical administration. Each AS normally uses a single interior gateway protocol (IGP) and metrics to propagate routing information within the set of routers. Also called a routing domain.

ASBR

Autonomous system boundary router. In OSPF, a router that exchanges routing information with routers in other ASs.

ASBR Summary LSA

OSPF link-state advertisement (LSA) sent by an area border router (ABR) to advertise the router ID of an autonomous system boundary router (ASBR) across an area boundary. See also ASBR.

AS external link advertisement

OSPF link-state advertisement sent by AS boundary routers to describe external routes that they have detected. These link-state advertisements are flooded throughout the AS (except for stub areas).

ASIC

Application-specific integrated circuit. Specialized processors that perform specific functions on the router.

ASM

The acronym ASM can be either of the following:

1. Adaptive Services Module. On a Juniper Networks M7i router, provides the same functionality as the AS PIC.
2. Any Source Multicast. Method of allowing a multicast receiver to listen to all traffic sent to a multicast group, regardless of its source.

AS path

In BGP, the route to a destination. The path consists of the AS numbers of all routers that a packet must go through to reach a destination.

AS PIC

Adaptive Services PIC. See adaptive services.

asymmetrical digital subscriber line

See ADSL.

Asynchronous Transfer Mode

See ATM.

ATM

Asynchronous Transfer Mode. A high-speed multiplexing and switching method utilizing fixed-length cells of 53 octets to support multiple types of traffic.

ATM adaption layer

See AAL.

ATM line interface

See ALI.

ATM-over-ADSL interface

Asynchronous Transfer Mode (ATM) interface used to send network traffic through a point-to-point connection to a DSL access multiplexer (DSLAM). ATM-over-ADSL interfaces are intended for asymmetrical digital subscriber line (ADSL) connections only, not for direct ATM connections.

atomic

Smallest possible operation. An atomic operation is performed either entirely or not at all. For example, if machine failure prevents a transaction from finishing, the system is rolled back to the start of the transaction, with no changes taking place.

AUC

Authentication center. Part of the Home Location Register (HLR) in third-generation (3G) systems; performs computations to verify and authenticate a mobile phone user.

authentication center

See AUC.

authentication header

See AH.

automatic policing

Policer that allows you to provide strict service guarantees for network traffic. Such guarantees are especially useful in the context of differentiated services for traffic engineered LSPs, providing better emulation for ATM wires over an MPLS network.

Automatic Protection Switching

See APS.

autonegotiation

Used by Ethernet devices to configure interfaces automatically. If interfaces support different speeds or different link modes (half duplex or full duplex), the devices attempt to settle on the lowest common denominator.

autonomous system

See AS.

autonomous system boundary router

See ASBR.

autonomous system external link advertisement

OSPF link-state advertisement sent by autonomous system boundary routers to describe external routes that they have detected. These link-state advertisements are flooded throughout the autonomous system (except for stub areas).

autonomous system path

In BGP, the route to a destination. The path consists of the autonomous system numbers of all the routers a packet must pass through to reach a destination.

auto-RP

Method of electing and announcing the rendezvous point-to-group address mapping in a multicast network. JUNOS software supports this vendor-proprietary specification. See also RP.

B

C

D

E

E1

High-speed WAN digital communication protocol that operates at a rate of 2.048 Mbps.

E3

High-speed WAN digital communication protocol that operates at a rate of 34.368 Mbps and uses time-division multiplexing to carry 16 E1 circuits.

EAL3

Common Criteria Evaluation Assurance Level 3. Evaluation Assurance Level is an assurance and compliance requirement defined by Common Criteria. Higher levels have more stringent requirements. See also Common Criteria.

early packet discard

See EPD.

EBGP

External BGP. A BGP configuration in which sessions are established between routers in different autonomous systems (ASs).

E-carrier

“E” stands for European. Standards that form part of the Synchronous Digital Hierarchy (SDH), in which groups of E1 circuits are bundled onto higher-capacity E3 links between telephone exchanges or countries. E-carrier standards are used just about everywhere in the world except North America and Japan, and are incompatible with the T-carrier standards.

ECC

Error checking and correction. The process of detecting errors during the transmission or storage of digital data and correcting them automatically. This usually involves sending or storing extra bits of data according to specified algorithms.

ECSA

Exchange Carriers Standards Association. A standards organization created after the divestiture of the Bell System to represent the interests of interexchange carriers.

edge router

In MPLS, a router located at the beginning or end of a label-switching tunnel. An edge router at the beginning of a tunnel applies labels to new packets entering the tunnel. An edge route at the end of a tunnel removes labels from packets exiting the tunnel. See also MPLS.

editor macros (Emacs)

Shortcut keystrokes used within the router’s command-line interface (CLI). These macros move the cursor and delete characters based on the sequence you specify.

EGP

Exterior gateway protocol; for example, BGP.

egress router

In MPLS, the last router in a label-switched path (LSP). See also ingress router.

EIA

Electronic Industries Association. A United States trade group that represents manufacturers of electronic devices and sets standards and specifications.

EIA-530

Serial interface that employs the EIA-530 standard for the interconnection of DTE and DCE equipment.

EIR

Equipment identity register. A mobile network database that contains information about devices using the network.

electromagnetic interference

See EMI.

electrostatic discharge

See ESD.

embedded OS software

Software used by a Juniper Networks router to operate the physical router components.

EMI

Electromagnetic interference. Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics or electrical equipment.

Encapsulating Security Payload

See ESP.

end system

In IS-IS, a network entity that sends and receives packets.

EPD

Early packet discard. For ATM2 interfaces only, a limit on the number of transmit packets that can be queued. Packets that exceed the limit are dropped. See also queue length.

ERO

Explicit Route Object. Extension to RSVP that allows an RSVP PATH message to traverse an explicit sequence of routers that is independent of conventional shortest-path IP routing.

error checking and correction

See ECC.

errored frame

Frame with one or more bits with errors. This frame will be dropped at the next Ethernet node and become a lost frame.

errored second

Period of a second with one or more errored or lost frames.

ESD

Electrostatic discharge. Stored static electricity that can damage electronic equipment and impair electrical circuitry when released.

ES-IS

End System–to–Intermediate System. Protocol that resolves Layer 3 ISO network service access points (NSAPs) to Layer 2 addresses. ES-IS resolution is similar to the way ARP resolves Layer 2 addresses for IPv4.

ESP

Encapsulating Security Payload. A protocol for securing packet flows for IPsec using encryption, data integrity checks, and sender authentication, which are added as a header to an IP packet. If an ESP packet is successfully decrypted, and no other party knows the secret key the peers share, the packet was not wiretapped in transit. See also AH.

Established

BGP neighbor state that represents a fully functional BGP peering session.

Ethernet

Local area network (LAN) technology used for transporting information from one location to another, formalized in the IEEE standard 802.3. Ethernet uses either coaxial cable or twisted-pair cable. Transmission speeds for data transfer range from the original 10 Mbps, to Fast Ethernet at 100 Mbps, to Gigabit Ethernet at 1000 Mbps.

ETSI

European Telecommunications Standardization Institute. A nonprofit organization that produces voluntary telecommunications standards used throughout Europe.

European Telecommunications Standardization Institute

See ETSI.

eventd

Event policy process that performs configured actions in response to events on a routing platform that trigger system log messages.

event policy process

See eventd.

exact

JUNOS software routing policy match type that represents only the route specified in a route filter.

exception packet

IP packet that is not processed by the normal packet flow through the Packet Forwarding Engine. Exception packets include local delivery information, expired TTL packets, and packets with an IP option specified.

Exchange

OSPF adjacency state in which two neighboring routers are actively sending database description packets to each other to exchange their database contents.

exclusive or

See XOR.

EXP bits

Experimental bits, also known as the class-of-service (CoS) bits, located in each MPLS label and used to encode the CoS value of a packet as it traverses an LSP.

explicit path

See signaled path.

Explicit Route Object

See ERO.

export

Placing of routes from the routing table into a routing protocol.

ExStart

OSPF adjacency state in which the neighboring routers negotiate to determine which router is in charge of the synchronization process.

Extensible Markup Language

See XML.

Extensible Stylesheet Language for Transformations

See XSLT.

exterior gateway protocol

See EGP.

external BGP

See EBGP.

external metric

Cost included in a route when OSPF exports route information from external autonomous systems. There are two types of external metrics: Type 1 and Type 2. Type 1 external metrics are equivalent to the link-state metric; that is, the cost of the route, used in the internal autonomous system. Type 2 external metrics are greater than the cost of any path internal to the autonomous system.

F

FA

Forwarding adjacency. RSVP LSP tunnel through which one or more other RSVP LSPs can be tunneled.

fabric schedulers

Identify a packet as high or low priority based on its forwarding class, and associate schedulers with the fabric priorities.

failover

Process by which a standby or secondary system component automatically takes over the functions of an active or primary component when the primary component fails or is temporarily shut down or removed for servicing. During failover, the system continues to perform normal operations with little or no interruption in service. See also GRES.

far-end alarm and control

See FEAC.

Fast Ethernet

Term encompassing a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbps, instead of the original Ethernet speed of 10 Mbps. See also Ethernet, Gigabit Ethernet.

fast port

Fast Ethernet port on a J4300 Services Router, and either a Fast Ethernet port or DS3 port on a J6300 Services Router. Only enabled ports are counted. A two-port Fast Ethernet PIM with one enabled port counts as one fast port. The same PIM with both ports enabled counts as two fast ports.

fast reroute

Mechanism for automatically rerouting traffic on an LSP if a node or link in an LSP fails, thus reducing the loss of packets traveling over the LSP.

FBF

Filter-based forwarding. A filter that classifies packets to determine their forwarding path within a router. FBF is used to redirect traffic for analysis.

FCS

Frame check sequence. A calculation that is added to a frame for error control. FCS is used in HDLC, Frame Relay, and other data-link layer protocols.

FDDI

Fiber Distributed Data Interface. A set of ANSI protocols for sending digital data over fiber-optic cable. FDDI networks are token-passing networks, and support data rates of up to 100 Mbps (100 million bits). FDDI networks are typically used as backbones for wide area networks.

FEAC

Far-end alarm and control. A T3 signal used to send alarm or status information from the far-end terminal back to the near-end terminal, and to initiate T3 loopbacks at the far-end terminal from the near-end terminal.

FEB

Forwarding Engine Board. In M5 and M10 routers, provides route lookup, filtering, and switching to the destination port.

FEC

Forwarding equivalence class. Criterion used to forward a set of packets, with similar or identical characteristics, using the same MPLS label. Forwarding equivalence classes are defined in the base LDP specification and can be extended through the use of additional parameters. FECs are also represented in other label distribution protocols.

FECN

Forward explicit congestion notification. In a Frame Relay network, a header bit transmitted by the source device requesting that the destination device slow down its requests for data. FECN and BECN minimize the possibility that packets will be discarded when more packets arrive than can be handled. See also BECN.

Federal Information Processing Standards

See FIPS.

Fiber Distributed Data Interface

See FDDI.

field-replaceable unit

See FRU.

FIFO

First in, first out. Scheduling method in which the first data packet stored in the queue is the first data packet removed from the queue. All JUNOS software interface queues operate in this mode by default.

File Transfer Protocol

See FTP.

filter

Process or device that screens packets based on certain characteristics, such as source address, destination address, or protocol, and forwards or discards packets that match the filter. Filters are used to control data packets or local packets. See also packet.

filter-based forwarding

See FBF.

FIPS

Federal Information Processing Standards. Defines, among other things, security levels for computer and networking equipment. FIPS is usually applied to military environments.

firewall

Security gateway positioned between two networks, usually between a trusted network and the Internet. A firewall ensures that all traffic that crosses it conforms to the organization’s security policy. Firewalls track and control communications, deciding whether to pass, reject, discard, encrypt, or log them. Firewalls also can be used to secure sensitive portions of a local network.

firewall filter

See stateful firewall filter, stateless firewall filter.

firmware

Instructions and data programmed directly into the circuitry of a hardware device for the purpose of controlling the device. Firmware is used for vital programs that must not be lost when the device is powered off.

first in, first out

See FIFO.

flap damping

See damping.

flapping

See route flapping.

flexible bandwidth allocation

See bandwidth on demand.

Flexible PIC Concentrator

See FPC.

floating static route

Route with an administrative distance greater than the administrative distance of the dynamically learned versions of the same route. The static route is used only when the dynamic routes are no longer available. When a floating static route is configured on an interface with a dialer filter, the interface can be used for backup.

flood and prune

Method of forwarding multicast data packets in a dense-mode network. Flooding and pruning occur every 3 minutes.

flow

Stream of routing information and packets that are handled by the Routing Engine and the Packet Forwarding Engine. The Routing Engine handles the flow of routing information between the routing protocols and the routing tables and between the routing tables and the forwarding tables, as well as the flow of local packets from the router physical interfaces to the Routing Engine. The Packet Forwarding Engine handles the flow of data packets into and out of the router physical interfaces.

flow collection interface

Interface that combines multiple cflowd records into a compressed ASCII data file and exports the file to an FTP server for storage and analysis, allowing users to manipulate the output from traffic monitoring operations.

flow control action

JUNOS software syntax used in a routing policy or firewall filter. It alters the default logical processing of the policy or filter when a set of match conditions is met.

flow monitoring

Application that monitors the flow of traffic and enables lawful interception of packets transiting between two routers. Traffic flows can be passively monitored by an offline router or actively monitored by a router participating in the network.

flow-tap application

Application that uses Dynamic Tasking Control Protocol (DTCP) requests to intercept IPv4 packets in an active monitoring router and send a copy of packets that match filter criteria to one or more content destinations. Flow-tap configurations can be used in flexible trend analysis for detecting new security threats and lawfully intercepting data.

forward explicit congestion notification

See FECN.

forwarding adjacency

See FA.

forwarding classes

Defined set of classes that are associated with each received packet on a router. These classes affect the forwarding, scheduling, and marking policies applied as the packet transits a routing platform. The forwarding class plus the loss priority define the per-hop behavior. Also known as ordered aggregates in the IETF Differentiated Services architecture.

Forwarding Engine Board

See FEB.

forwarding equivalence class

See FEC.

forwarding information base

See forwarding table.

forwarding table

JUNOS software forwarding information base. The JUNOS routing protocol process installs active routes from its routing tables into the Routing Engine forwarding table. The kernel copies this forwarding table into the Packet Forwarding Engine, which determines which interface transmits the packets.

FPC

Flexible PIC Concentrator. An interface concentrator on which PICs are mounted. An FPC is inserted into a slot in a Juniper Networks router. See also PIC.

fractional E1

Interface that contains one or more of the 32 DS0 time slots that can be reserved from an E1 interface. (The first time slot is reserved for framing.)

fractional interface

Interface that contains one or more DS0 time slots reserved from an E1 or T1 interface. Fractional interfaces allow service providers to provision part of an E1 or T1 interface to one customer and the other part to another customer. The individual fractional interfaces connect to different destinations, and customers pay for only the bandwidth fraction used and not for the entire E1 or T1 interface. Fractional interfaces can be configured on both channelized PICs and PIMs and unchannelized, regular E1 and T1 PICs and PIMs.

fractional T1

Interface that contains one or more of the 24 DS0 time slots that can be reserved from a T1 interface.

fragmentation

In TCP/IP, the process of breaking packets into the smallest maximum size packet data unit (PDU) supported by any of the underlying networks. In the Open Systems Interconnection (OSI) reference model, this process is known as segmentation. For JUNOS applications, split Layer 3 packets can then be encapsulated in MLFR or MLPPP for transport.

frame check sequence

See FCS.

Frame Relay

Efficient replacement for the older X.25 protocol that does not require explicit acknowledgment of each frame of data. Frame Relay allows private networks to reduce costs by using shared facilities between the end-point switches of a network managed by a Frame Relay service provider. Individual data-link connection identifiers (DLCIs) are assigned to ensure that each customer receives only its own traffic.

frequency-division multiplexed channel

Signals carried at different frequencies and transmitted over a single wire or wireless medium.

FRF

Frame Relay Forum. A technical committee that promotes Frame Relay by negotiating agreements and developing standards.

FRF.15

End-to-end Frame Relay Implementation Agreement. An implementation of MLFR using multiple virtual connections to aggregate logical bandwidth for end-to-end Frame Relay. Released by the Frame Relay Forum.

FRF.16

Multilink Frame Relay Implementation Agreement. An implementation of MLFR in which a single logical connection is provided by multiplexing multiple physical interfaces for user-to-network interface and network-to-network interface (UNI/NNI) connections. Released by the Frame Relay Forum.

FRU

Field-replaceable unit. A router component that customers can replace onsite.

FTP

File Transfer Protocol. Application protocol that is part of the TCP/IP protocol stack. Used for transferring files between network nodes. FTP is defined in RFC 959.

Full

OSPF adjacency state that represents a fully functional neighbor relationship.

fxp0

See management Ethernet interface.

fxp1

JUNOS software permanent interface used for communications between the Routing Engine and the Packet Forwarding Engine. This interface is not present in all routers.

fxp2

JUNOS software permanent interface used for communications between the Routing Engine and the Packet Forwarding Engine. This interface is not present in all routers.

G

G.992.1

See ITU-T Rec. G.992.1.

G.SHDSL

Symmetric high-speed digital subscriber line (SHDSL). Standard published in 2001 by the ITU-T with recommendation ITU G.991.2 G.SHDSL. G.SHDSL incorporates features of other DSL technologies such as asymmetrical DSL (ADSL). See also SHDSL, ADSL.

Garbage Collection Timer

Timer used in a distance-vector network that represents the time remaining before a route is removed from the routing table.

G-CDR

GGSN call detail record. Collection of charges in ASN.1 format that is eventually billed to a mobile station user.

Generalized Multiprotocol Label Switching

See GMPLS.

generated route

Summary route that uses an IP address next hop to forward packets in an IP network. A generated route is functionally similar to an aggregated route.

generic routing encapsulation

See GRE.

GGSN

Gateway GPRS support node. A router that serves as a gateway between mobile networks and packet data networks.

Gigabit Ethernet

Term describing various technologies for implementing Ethernet networking at a nominal speed of one gigabit per second. Gigabit Ethernet is supported over both optical fiber and twisted-pair cable. Physical layer standards include 1000BASE-T, 1 Gbps over CAT-5e copper cabling, and 1000BASE-SX for short to medium distances over fiber. See also Ethernet, Fast Ethernet.

Global System for Mobile Communications

See GSM.

GMPLS

Generalized Multiprotocol Label Switching. A protocol that extends the functionality of MPLS to include a wider range of label-switched path (LSP) options for a variety of network devices.

GMT

See UTC.

GPRS

General Packet Radio System. A packet-switched service that allows full mobility and wide-area coverage as information is sent and received across a mobile network.

graceful restart

Process that allows a router whose control plane is undergoing a restart to continue to forward traffic while recovering its state from neighboring routers. Without graceful restart, a control plane restart disrupts services provided by the router.

graceful Routing Engine switchover

See GRES.

graceful switchover

JUNOS software feature that allows a change from the primary device, such as a Routing Engine, to the backup device without interruption of packet forwarding.

gratuitous ARP

Broadcast request for a router’s own IP address to check whether that address is being used by another node. Primarily used to detect IP address duplication.

GRE

Generic routing encapsulation. A general tunneling protocol that can encapsulate many types of packets to enable data transmission through a tunnel. GRE is used with IP to create a virtual point-to-point link to routers at remote points in a network. See also tunneling protocol.

GRES

Graceful Routing Engine switchover. In a router that contains a master and a backup Routing Engine, allows the backup Routing Engine to assume mastership automatically, with no disruption of packet forwarding.

group

Collection of related BGP peers.

group address

IP address used as the destination address in a multicast IP packet. The group address functionally represents the senders and interested receivers for a particular multicast data stream.

GSM

Global System for Mobile Communications. A second-generation (2G) mobile wireless networking standard defined by ETSI that uses TDMA technology and operates in the 900-MHz radio band. See also TDMA.

GTP

GPRS tunneling protocol. A protocol that transports IP packets between an SGSN and a GGSN. See also tunneling protocol.

GTP-C

GGSN tunneling protocol, control. A protocol that allows an SGSN to establish packet data network access for a mobile station. See also tunneling protocol.

GTP-U

GGSN tunneling protocol, user plane. A protocol that carries mobile station user data packets. See also tunneling protocol.

H

I

I/O Manager ASIC

Juniper Networks ASIC responsible for segmenting data packets into 64-byte J-cells and for queuing result cells before transmission.

IANA

Internet Assigned Numbers Authority. A regulatory group that maintains all assigned and registered Internet numbers, such as IP and multicast addresses. See also NIC.

IBGP

Internal BGP. A BGP configuration in which sessions are established between routers in the same autonomous system (AS).

ICMP

Internet Control Message Protocol. Used in router discovery, ICMP allows router advertisements that enable a host to discover addresses of operating routers on the subnet.

ICMP Router Discovery Protocol

See IRDP.

IDE

Integrated Drive Electronics. Type of hard disk on a Routing Engine.

IDEA

International Data Encryption Algorithm. An algorithm that uses a 128-bit key and is one of the methods at the heart of Pretty Good Privacy (PGP). IDEA is patented by Ascom Tech AG and is popular in Europe.

Idle

Initial BGP neighbor state in which the local router refuses all incoming session requests.

IDS

Intrusion detection service. A service that inspects all inbound and outbound network activity and identifies suspicious patterns that may indicate a network or system attack from someone attempting to break into or compromise a system.

IEC

International Electrotechnical Commission. See ISO.

IEEE

Institute of Electrical and Electronics Engineers. An international professional society for electrical engineers.

IETF

Internet Engineering Task Force. An international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet.

IFD

(A Juniper Networks internal use acronym.) See physical interface.

IFF

(A Juniper Networks internal use acronym.) See protocol families.

IFL

(A Juniper Networks internal use acronym.) See logical interface.

I-frame

Information frame used to transfer data in sequentially numbered logical link control protocol data units (LPDUs) between link stations.

IGMP

Internet Group Management Protocol. A host-to-router signaling protocol for IPv4, used to determine whether group members are present during IP multicasting.

IGP

Interior gateway protocol, such as IS-IS, OSPF, or RIP.

IKE

Internet Key Exchange. Part of IPsec that provides ways to securely negotiate the shared private keys that the AH and ESP portions of IPsec need to function properly. IKE employs Diffie-Hellman methods and is optional in IPsec (the shared keys can be entered manually at the endpoints).

ILMI

Integrated Local Management Interface. A specification developed by the ATM Forum that incorporates network management capabilities into the ATM user-to-network interface (UNI) and provides bidirectional exchange of management information between UNI management entities (UMEs).

IMEI

International Mobile Station Equipment Identity. A unique code used to identify an individual mobile station to a GSM network.

import

Installation of routes from the routing protocols into a routing table.

IMSI

International Mobile Subscriber Identity. Information that identifies a particular subscriber to a GSM network.

IMT-2000

International Mobile Telecommunications 2000. Global standard for third-generation (3G) wireless communications, defined by a set of interdependent ITU Recommendations. IMT-2000 provides a framework for worldwide wireless access by linking the diverse systems of terrestrial and satellite-based networks.

inet.0

Default JUNOS software routing table for IPv4 unicast routers.

inet.1

Default JUNOS software routing table for storing the multicast cache for active data streams in the network.

inet.2

Default JUNOS software routing table for storing unicast IPv4 routes specifically used to prevent forwarding loops in a multicast network.

inet.3

Default JUNOS software routing table for storing the egress IP address of an MPLS label-switched path.

inet.4

Default JUNOS software routing table for storing information generated by the Multicast Source Discovery Protocol (MSDP).

inet6.0

Default JUNOS software routing table for storing unicast IPv6 routes.

infinity metric

Metric value used in distance-vector protocols to represent an unusable route. For RIP, the infinity metric is 16.

ingress router

In MPLS, the first router in a label-switched path (LSP). See also egress router.

Init

OSPF adjacency state in which the local router has received a hello packet but bidirectional communication is not yet established.

insert

JUNOS software command that allows a user to reorder terms in a routing policy or a firewall filter, or change the order of a policy chain.

instance.inetflow.0

Routing table that shows route flows through BGP.

integrated bridging and routing

See IBR.

Integrated Drive Electronics

See IDE.

Integrated Local Management Interface

See ILMI.

Integrated Services Digital Network

See ISDN.

intelligent queuing

See IQ.

inter-AS routing

Routing of packets among different autonomous systems (ASs). See also EBGP.

intercluster reflection

In a BGP route reflection, the redistribution of routing information by a route reflector system to all nonclient peers (BGP peers not in the cluster). See also route reflection.

interface cost

Value added to all received routes in a distance-vector network before they are placed into the routing table. The JUNOS software uses a cost of 1 for this value.

interface preservation

See link state replication.

interface routes

Routes that are in the routing table because an interface has been configured with an IP address. Also called direct routes.

intermediate system

In IS-IS, the network entity that sends and receives packets and can also route packets.

internal BGP

See IBGP.

International Data Encryption Algorithm

See IDEA.

International Mobile Station Equipment Identity

See IMEI.

International Mobile Subscriber Identity

See IMSI.

International Mobile Telecommunications-2000

See IMT-2000.

International Organization for Standardization

See ISO.

International Telecommunication Union

See ITU-T.

Internet Assigned Numbers Authority

See IANA.

Internet Control Message Protocol

See ICMP.

Internet Engineering Task Force

See IETF.

Internet Group Management Protocol

See IGMP.

Internet Key Exchange

See IKE.

Internet Processor ASIC

Juniper Networks ASIC responsible for using the forwarding table to make routing decisions within the Packet Forwarding Engine. The Internet Processor ASIC also implements firewall filters.

Internet Protocol

See IP.

Internet Security Association and Key Management Protocol

See ISAKMP.

Internet service provider

See ISP.

interprovider VPN

VPN that provides connectivity between separate autonomous systems (ASs) with separate border edge routers. It is used by VPN customers who have connections to several different ISPs, or different connections to the same ISP in different geographic regions, each of which has a different AS.

intra-AS routing

Routing of packets within a single autonomous system (AS). See also IBGP.

intrusion detection service

See IDS.

IP

Internet Protocol. The protocol used for sending data from one point to another on the Internet.

IP Control Protocol

See IPCP.

IPCP

IP Control Protocol. Protocol that establishes and configures IP over the Point-to-Point Protocol (PPP).

IPsec

IP Security. A standard way to add security to Internet communications. The secure aspects of IPsec are usually implemented in three parts: the authentication header (AH), the Encapsulating Security Payload (ESP), and the Internet Key Exchange (IKE).

IP Security

See IPsec.

IP television

See IPTV.

IPTV

IP television. A system using the Internet protocol to deliver digital television service over a network.

IQ

Intelligent queuing. M-series and T-series routing platform interfaces that offer granular quality-of-service (QoS) capabilities; extensive statistics on packets and bytes that are transmitted, received, or dropped; and embedded diagnostic tools.

IRB

Integrated bridging and routing. IRB provides simultaneous support for Layer 2 (L2) bridging and Layer 3 (L3) routing within the same bridge domain. Packets arriving on an interface of the bridge domain are L2 switched or L3 routed based on the destination MAC address. Packets addressed to the router’s MAC address are routed to other L3 interfaces.

IRDP

ICMP Router Discovery Protocol. A protocol that enables a host to determine the address of a router that it can use as a default gateway.

ISAKMP

Internet Security Association and Key Management Protocol. A protocol that allows the receiver of a message to obtain a public key and use digital certificates to authenticate the sender’s identity. ISAKMP is key exchange independent; that is, it supports many different key exchanges. See also IKE, Oakley.

ISDN

Integrated Services Digital Network. A set of digital communications standards that enable the transmission of information over existing twisted-pair telephone lines at higher speeds than standard analog telephone service. An ISDN interface provides multiple B-channels (bearer channels) for data and one D-channel for control and signaling information. See also B-channel, D-channel.

I-SID

24-bit service instance identifier field carried inside an I-TAG. The I-SID defines the service instance to which the frame is mapped.

IS-IS

Intermediate System-to-Intermediate System. A link-state, interior gateway routing protocol for IP networks that uses the shortest-path-first (SPF) algorithm to determine routes.

ISO

International Organization for Standardization. A worldwide federation of standards bodies that promotes international standardization and publishes international agreements as International Standards.

ISP

Internet service provider. Company that provides access to the Internet and related services.

I-TAG

A field defined in the IEEE 802.1ah provider MAC encapsulation header that carries the service instance information (I-SID) associated with the frame.

ITU-T

International Telecommunication Union Telecommunication Standardization (formerly known as the CCITT). Group supported by the United Nations that makes recommendations and coordinates the development of telecommunications standards for the entire world.

ITU-T Rec. G.992.1

International standard that defines ADSL. Annex A defines how ADSL works over twisted-pair copper (POTS) lines. Annex B defines how ADSL works over ISDN lines.

J

jbase

JUNOS software package containing updates to the kernel.

jbundle

JUNOS software package containing all possible software package files.

J-cell

A 64-byte data unit used within the Packet Forwarding Engine. All IP packets processed by a Juniper Networks router are segmented into J-cells.

JCS

See Juniper Control System.

JCS management module (MM)

Chassis management hardware and software used to access and configure the Juniper Control System (JCS) platform.

JCS switch module

Hardware device that connects Routing Engines in the Juniper Control System (JCS) chassis to a Juniper Networks router and controls traffic between the two devices. For redundancy, the JCS chassis can include two JCS switch modules.

jdocs

JUNOS software package containing the documentation set.

jitter

Small random variation introduced into the value of a timer to prevent multiple timer expirations from becoming synchronized. In real-time applications such as VoIP and video, variation in the rate at which packets in a stream are received that can cause quality degradation.

jkernel

JUNOS software package containing the basic components of the software.

Join message

PIM message sent hop by hop upstream toward a multicast source or the RP of the domain. It requests that multicast traffic be sent downstream to the router originating the message.

jpfe

JUNOS software package containing the embedded OS software for operating the Packet Forwarding Engine.

jroute

JUNOS software package containing the software used by the Routing Engine.

Juniper Control System (JCS)

OEM blade server customized to work with Juniper Networks routers. The JCS chassis holds up to 12 single Routing Engines (or 6 redundant Routing Engine pairs). The JCS 1200 chassis enables the control plane and forwarding plane of a single interconnected platform to be scaled independently.

J-Web

Graphical Web browser interface to the JUNOS Internet software on routing platforms. With the J-Web interface, you can monitor, configure, diagnose, and manage the routing platform from a PC or laptop that has Hypertext Transfer Protocol (HTTP) or HTTP over Secure Sockets Layer (HTTPS) enabled.

K

keepalive message

Message sent between network devices to inform each other that they are still active.

kernel

Basic software component of the JUNOS software. The kernel operates the various processes used to control the router’s operations.

kernel forwarding table

See forwarding table.

key management process

See kmd.

kmd

Key management process that provides IPsec authentication services for encryption PICs.

L

L2TP

Layer 2 Tunneling Protocol. A procedure for secure communication of data across a Layer 2 network that enables users to establish PPP sessions between tunnel endpoints. L2TP uses profiles for individual user and group access to ensure secure communication that is as transparent as possible to both end users and applications. See also tunneling protocol.

label

In MPLS, a 20-bit unsigned integer from 0 through 1,048,575, used to identify a packet traveling along an LSP.

Label Distribution Protocol

See LDP.

label object

RSVP message object that contains the label value allocated to the next downstream router.

label pop operation

Function performed by an MPLS router in which the top label in a label stack is removed from the data packet.

label push operation

Function performed by an MPLS router in which a new label is added to the top of the data packet.

label request object

RSVP message object that requests each router along the path of an LSP to allocate a label for forwarding.

label swap operation

Function performed by an MPLS router in which the top label in a label stack is replaced with a new label before the data packet is forwarded to the next-hop router.

label-switched interface

See LSI.

label-switched path

See LSP.

label switching

See MPLS.

label-switching router

See LSR.

label values

20-bit field in an MPLS header used by routers to forward data traffic along an MPLS label-switched path.

LAN PHY

Local Area Network Physical Layer Device. A physical layer device that allows 10-Gigabit Ethernet wide area links to use existing Ethernet applications. See also PHY and WAN PHY.

Layer 2 circuits

Collection of transport modes that accept a stream of ATM cells, convert them to an encapsulated Layer 2 format, then tunnel them over an MPLS or IP backbone, where a similarly configured routing platform segments these packets back into a stream of ATM cells, to be forwarded to the virtual circuit configured for the far-end routing platform. Layer 2 circuits are designed to transport Layer 2 frames between provider edge (PE) routing platforms across a Label Distribution Protocol (LDP)-signaled MPLS backbone. See also AAL5 mode, cell-relay mode, standard AAL5 mode, trunk mode.

Layer 2 Tunneling Protocol

See L2TP.

Layer 2 VPN

Provides a private network service among a set of customer sites using a service provider’s existing MPLS and IP network. A customer’s data is separated from other data using software rather than hardware. In a Layer 2 VPN, the Layer 3 routing of customer traffic occurs within the customer’s network.

Layer 3 VPN

Provides a private network service among a set of customer sites using a service provider’s existing MPLS and IP network. A customer’s routes and data are separated from other routes and data using software rather than hardware. In a Layer 3 VPN, the Layer 3 routing of customer traffic occurs within the service provider’s network.

LCC

Line-card chassis. Term used by the JUNOS command-line interface (CLI) to refer to a T640 routing node in a routing matrix.

LCP

Link Control Protocol. A traffic controller used to establish, configure, and test data-link connections for the Point-to-Point Protocol (PPP).

LDAP

Lightweight Directory Access Protocol. Software protocol used for locating resources on a public or private network.

LDP

Label Distribution Protocol. A protocol for distributing labels in non-traffic-engineered applications. LDP allows routers to establish label-switched paths (LSPs) through a network by mapping network-layer routing information directly to data-link layer switched paths.

leaf node

Terminating node of a multicast distribution tree. A router that is a leaf node only has receivers and does not forward multicast packets to other routers.

learning domain

MAC address database where MAC addresses are added based on the normalized VLAN tags.

LFI

Link fragmentation and interleaving. A method that reduces excessive delays by fragmenting long packets into smaller packets and interleaving them with real-time frames. For example, short delay-sensitive packets, such as packetized voice, can race ahead of larger delay-insensitive packets, such as common data packets.

LFM

Link fault management. A method used to detect problems on links and spans on an Ethernet network defined in IEEE 802.3ah. See also OAM.

liblicense

Library that includes messages generated for routines for software license management.

libpcap

Implementation of the pcap application programming interface. libpcap is used by a program to capture packets traveling over a network. See also pcap.

Lightweight Directory Access Protocol

See LDAP.

limited operational environment

Term used to describe the restrictions placed on FIPS-certified equipment. See FIPS.

line-card chassis

See LCC.

line loopback

Method of troubleshooting a problem with physical transmission media in which a transmission device in the network sends the data signal back to the originating router.

link

Communication path between two neighbors. A link is up when communication is possible between the two end points.

Link Control Protocol

See LCP.

link fault management

See LFM.

link fragmentation and interleaving

See LFI.

Link Management Protocol

See LMP.

link protection

Method of establishing bypass label-switched paths (LSPs) to ensure that traffic going over a specific interface to a neighboring router can continue to reach the router if that interface fails. The bypass LSP uses a different interface and path to reach the same destination.

link services intelligent queuing interfaces

See LSQ.

link-state acknowledgement

OSPF data packet used to inform a neighbor that a link-state update packet has been successfully received.

link-state advertisement

See LSA.

link-state database

All routing knowledge in a link-state network is contained in this database. Each router runs the SPF algorithm against this database to locate the best network path to each destination in the network.

link-state PDU

Packet that contains information about the state of adjacencies to neighboring systems.

link-state replication

Addition to the SONET Automatic Protection Switching (APS) functionality that helps promote redundancy of the link PICs used in LSQ configurations. If the active SONET PIC fails, links from the standby PIC are used without causing a link renegotiation. Also called interface preservation.

link-state request list

List generated by an OSPF router during the exchange of database information while forming an adjacency. Advertised information by a neighbor that the local router does not contain is placed in this list.

link-state request packet

OSPF data packet used by a router to request database information from a neighboring router.

link-state update

OSPF data packet that contains one of multiple LSAs. It is used to advertise routing knowledge into the network.

linktrace message

See LTM.

Linktrace Protocol

Protocol used for path discovery between a pair of maintenance points. Linktrace messages are triggered by an administrator using the traceroute command to verify the path between a pair of maintenance end points (MEPs) under the same maintenance association. Linktrace messages can also be used to verify the path between an MEP and a maintenance intermediate point (MIP) under the same maintenance domain. The operation of IEEE 802.1ag linktrace request and response messages is similar to the operation of Layer 3 traceroute commands.

linktrace response

See LTR.

LLC

Logical link control. Data-link layer protocol used on a LAN. LLC1 provides connectionless data transfer, and LLC2 provides connection-oriented data transfer.

LLC frame

Unit of data that contains specific information about the LLC layer and identifies line protocols associated with the layer. See also LLC.

LMI

Local Management Interface. Enhancements to the basic Frame Relay specifications, providing support for the following:

• A keepalive mechanism that verifies the flow of data
• A multicast mechanism that provides a network server with a local DLCI and multicast DLCI
• In Frame Relay networks, global addressing that gives DLCIs global instead of local significance
• A status mechanism that provides a switch with ongoing status reports on known DLCIs

LMP

Link Management Protocol. Part of GMPLS, a protocol used to define a forwarding adjacency between peers and to maintain and allocate resources on the traffic engineering links.

lo0

See loopback interface (lo0).

load balancing

Process that installs all next-hop destinations for an active route in the forwarding table. You can use load balancing across multiple paths between routers. The behavior of load balancing depends on the version of the Internet Processor ASIC in the router. Also called per-packet load balancing.

loading

OSPF adjacency state in which the local router sends link-state request packets to its neighbor and waits for the appropriate link-state updates from that neighbor.

Local Management Interface

See LMI.

local packet

Chunk of data destined for or sent by the Routing Engine.

local preference

Optional BGP path attribute carried in internal BGP update packets that indicates the degree of preference for an external route.

local RIB

Logical software table that contains BGP routes used by the local router to forward data packets.

local significance

Concept used in an MPLS network where the label values are unique only between two neighbor routers.

logical interface

On a physical interface, the configuration of one or more units which include all addressing, protocol information, and other logical interface properties that enable the physical interface to function.

logical link control

See LLC.

logical operator

Characters used in a firewall filter to represent a Boolean AND or OR operation.

logical router

See logical system.

logical system

Logical routing device that is partitioned from an M-series or T-series routing platform. Each logical system independently performs a subset of the tasks performed by the main router and has a unique routing table, interfaces, policies, and routing instances.

longer

JUNOS software routing policy match type that represents all routes more specific than the given subnet, but not the given subnet itself. It is similar to a mathematical greater-than operation.

loopback interface (lo0)

Interface that is always available because it is independent of any physical interfaces. When configured with an address, the loopback interface is the default address for the routing platform and any unnumbered interfaces. See also unnumbered interface.

loose hop

In the context of traffic engineering, a path that can use any router or any number of other intermediate (transit) points to reach the next address in the path. (Definition from RFC 791, modified to fit LSPs.)

loss-priority map

Maps the loss priority of incoming packets based on code point values.

lower-speed IQ interfaces

E1, NxDS0, and T1 interfaces configured on an IQ PIC.

LPDU

LLC protocol data unit. LLC frame on a DLSw network. See LLC frame.

LSA

Link-state advertisement. OSPF data structure that is advertised in a link-state update packet. Each LSA uniquely describes a portion of the OSPF network.

LSI

Label-switched interface. A logical interface supported by the JUNOS software that provides VPN services (such as VPLS and Layer 3 VPNs) normally provided by a Tunnel Services PIC.

LSP

Label-switched path. Sequence of routers that cooperatively perform MPLS operations for a packet stream. The first router in an LSP is called the ingress router, and the last router in the path is called the egress router. An LSP is a point-to-point, half-duplex connection from the ingress router to the egress router. (The ingress and egress routers cannot be the same router.) See link-state PDU.

LSQ

Link services intelligent queuing interfaces. Interfaces configured on the Adaptive Services PIC or ASM that support MLPPP and MLFR traffic and also fully support JUNOS class-of-service (CoS) components.

LSR

Label-switching router. A router on which MPLS is enabled and that can process label-switched packets.

LTM

Linktrace message. Message used by one MEP to trace the path to another maintenance end point (MEP) or maintenance intermediate point (MIP) in the same domain. It is needed for loopback (ping). All intermediate MIPs respond back with a linktrace response to the originating MEP. After decreasing the TTL by one, intermediate MIPs forward the linktrace message until the destination MIP/MEP is reached. If the destination is a MEP, every MIP along a given maintenance association responds to the originating MEP. The originating MEP can then determine the MAC address of all MIPs along the maintenance association and their precise location with respect to the originating MEP.

LTR

Linktrace response. See LTM.

M

MAC

Media access control. In the OSI seven-layer networking model defined by the IEEE, MAC is the lower sublayer of the data link layer. The MAC sublayer governs protocol access to the physical network medium. By using the MAC addresses that are assigned to all ports on a router, multiple devices on the same physical link can uniquely identify one another at the data link layer. See also MAC address.

MAC address

Serial number permanently stored in a device adapter to uniquely identify the device. See also MAC.

maintenance association

Combined set of nodes (MEPs and MIPs) within a maintenance domain. See also LTR.

maintenance association end point

See MEP.

maintenance association ID

ID associated with the maintenance association.

maintenance association intermediate point

See MIP.

maintenance domain

Part of the network where connectivity fault detection is performed.

maintenance point

See MP.

MAM

Maximum allocation bandwidth constraints model. In Differentiated Services–aware traffic engineering, a constraint model that divides the available bandwidth among the different classes. Sharing of bandwidth among the class types is not allowed.

management daemon

See mgd.

management Ethernet interface

Permanent interface that provides an out-of-band method, such as SSH and telnet, to connect to the routing platform. SNMP can use the management interface to gather statistics from the routing platform. Called fxp0 on some routing platforms. See also permanent interface.

Management Information Base

See MIB.

Management Module, JCS

See JCS Management Module.

mapping agent

Router used in an auto-RP multicast network to select the rendezvous point for all multicast group addresses. The rendezvous point is then advertised to all other routers in the domain.

martian address

Network address about which all information is ignored.

martian route

Network routes about which all information is ignored. The JUNOS software does not allow martian routes in the inet.0 routing table.

MAS

Mobile network access subsystem. A GSN application subsystem that contains the access server.

mask

See subnet mask.

master

Router in control of the OSPF database exchange during an adjacency formation.

match

Logical concept used in a routing policy or firewall filter. A match denotes the criteria used to find a route or IP packet before an action is performed.

match type

JUNOS software syntax used in a route filter to better describe the routes that should match the policy term.

maximum allocation bandwidth constraints model

See MAM.

maximum received reconstructed unit

See MRRU.

maximum transmission unit

See MTU.

MBGP

Multiprotocol Border Gateway Protocol. An extension to BGP that allows you to connect multicast topologies within and between BGP ASs.

MBone

Multicast Backbone. An interconnected set of subnetworks and routers that support the delivery of IP multicast traffic. The MBone is a virtual network that is layered on top of sections of the physical Internet.

MCS

Miscellaneous Control Subsystem. On the M40e and M160 routers, provides control and monitoring functions for router components and SONET clocking for the router.

MD5

Message Digest 5. A one-way hashing algorithm that produces a 128-bit hash used for generating message authentication signatures. MD5 is used in AH and ESP. See also hashing, SHA-1.

MDRR

Modified deficit round robin. A method for selecting queues to be serviced. See queue.

MDT

Multicast distribution tree. The path between the sender (host) and the multicast group (receiver or listener).

mean time between failures

See MTBF.

MED

Multiple exit discriminator. An optional BGP path attribute consisting of a metric value that is used to determine the exit point to a destination when all other factors determining the exit point are equal.

MEP

Start and end point within a maintenance domain. See also LTM.

mesh

Network topology in which devices are organized in a manageable, segmented manner with many, often redundant, interconnections between network nodes.

message aggregation

Extension to the Resource Reservation Protocol (RSVP) specification that allows neighboring routers to bundle up to 30 RSVP messages into a single protocol packet.

Message Digest 5

See MD5.

mgd

Management daemon. JUNOS software process responsible for managing all user access to the router.

MIB

Management Information Base. Definition of an object that can be managed by SNMP.

midplane

Physically separates front and rear cavities inside the chassis, distributes power from the power supplies, and transfers packets and signals between router components, which plug into it.

MIP

Intermediate node within the maintenance domain. See also LTM.

Miscellaneous Control Subsystem

See MCS.

MLD

Multicast listener discovery. Protocol that manages the membership of hosts and routers in multicast groups. IPv6 multicast routers use MLD to learn, for each of their attached physical networks, which groups have interested listeners.

MLFR

Multilink Frame Relay. Logically ties together individual circuits, creating a bundle. The logical equivalent of MLPPP, MLFR is used for Frame Relay traffic instead of PPP traffic. FRF.15 and FRF.16 are two implementations of MLFR.

MLPPP

Multilink Point-to-Point Protocol. Enables you to bundle multiple PPP links into a single logical link between two network devices to provide an aggregate amount of bandwidth. The technique is often called bonding or link aggregation. Defined in RFC 1990. See also PPP.

MM

JCS management module.

MMF

Multimode fiber. Optical fiber supporting the propagation of multiple frequencies of light. MMF is used for relatively short distances because the modes tend to disperse over longer lengths (called modal dispersion). For longer distances, single-mode fiber (sometimes called monomode) is used. See also single-mode fiber.

mobile network access subsystem

See MAS.

mobile point-to-point control subsystem

See MPS.

mobile station

Mobile device, such as a cellular phone or a mobile personal digital assistant (PDA).

Mobile Station Integrated Services Digital Network Number

See MSISDN.

Mobile Switching Center

See MSC.

mobile transport subsystem

See MTS.

MPLS

Multiprotocol Label Switching. Mechanism for engineering network traffic patterns that functions by assigning to network packets short labels that describe how to forward them through the network. Also called label switching. See also traffic engineering.

MPLS EXP classifier

Class-of-service (CoS) behavior classifier for classifying packets based on the MPLS experimental bit. See also EXP bits.

MPS

Mobile point-to-point control subsystem. A GSN application subsystem that controls all functionality associated with a particular connection.

MRRU

Maximum received reconstructed unit. Similar to the MTU, but is specific to link services interfaces. See also MTU.

MSA

Multisource Agreement. Definition of a fiber-optic transceiver module that conforms to the 10-Gigabit Ethernet standard. See also XENPAK module.

MSC

Mobile Switching Center. Provides origination and termination functions to calls from a mobile station user.

MSDP

Multicast Source Discovery Protocol. A protocol used to connect multicast routing domains to allow the domains to discover multicast sources from other domains. It typically runs on the same router as the PIM sparse mode rendezvous point (RP).

MSISDN

Mobile Station Integrated Services Digital Network Number. A number that callers use to reach a mobile services subscriber.

MST

See MSTP.

MSTI

Multiple Spanning Tree Instance. One of a number of spanning trees calculated by MSTP within an MST region. The MSTI provides a simple and fully connected active topology for frames classified as belonging to a VLAN that is mapped to the MSTI by the MST configuration table used by the MST bridges of that MST region. See also CIST.

MSTP

Multiple Spanning Tree Protocol. Spanning-tree protocol used to prevent loops in bridge configurations. Unlike other types of STPs, MSTP can block ports selectively by VLAN. See also RSTP.

MTBF

Mean time between failures. Measure of hardware component reliability.

MTS

Mobile transport subsystem. A GSN application subsystem that implements all the protocols used by the GSN.

MTU

Maximum transmission unit. Limit on the data size for a network.

multicast

Operation of sending network traffic from one network node to multiple network nodes.

multicast distribution tree

See MDT.

multicast listener discovery

See MLD.

multicast-scope number

Number used for configuring the multicast scope. Configuring a scope number constrains the scope of a multicast session. The number value can be any hexadecimal number from 0 through F. The multicast-scope value is a number from 0 through 15, or a specified keyword with an associated prefix range. For example, link-local (value=2), corresponding prefix 224.0.0.0/24.

Multicast Source Discovery Protocol

See MSDP.

multiclass LSP

In Differentiated Services–aware traffic engineering, a multiclass label-switched path (LSP) functions like a standard LSP, but also allows you to reserve bandwidth for multiple class types. The experimental (EXP) bits of the MPLS header are used to distinguish between class types.

multiclass MLPPP

Enables multiple classes of service when you use MLPPP. Defined in RFC 2686, The Multi-Class Extension to Multi-Link PPP.

multifield classifier

Method for classifying traffic flows. Unlike a behavior aggregate (BA) classifier, a multifield classifier examines multiple fields in the packet to apply class-of-service (CoS) settings. Examples of fields that a multifield classifier examines include the source and destination address of the packet, as well as the source and destination port numbers of the packet. See also BA classifier, classification.

multihoming

Network topology that uses multiple connections between customer and provider devices to provide redundancy.

Multilink Frame Relay

See MLFR.

multimode fiber

See MMF.

multiple exit discriminator

See MED.

multiple spanning tree instance

See MSTI.

Multiple Spanning Tree Protocol

See MSTP.

multiprotocol BGP

See MBGP.

Multiprotocol Label Switching

See MPLS.

Multisource Agreement

See MSA.

MVS

Mobile visitor register subsystem.

N

named path

JUNOS software syntax that specifies a portion of or the entire network path that should be used as a constraint in signaling an MPLS label-switched path.

NAPT

Network Address Port Translation. A method that translates the addresses and transport identifiers of many private hosts into a few external addresses and transport identifiers to make efficient use of globally registered IP addresses. NAPT extends the level of translation beyond that of basic NAT. See also NAT.

NAT

Network Address Translation. A method of concealing a set of host addresses on a private network behind a pool of public addresses. It can be used as a security measure to protect the host addresses from direct targeting in network attacks.

National Institute of Standards and Technology

See NIST.

NCP

Network Control Protocol. A traffic controller used to establish and configure different network layer protocols for the Point-to-Point Protocol (PPP).

NDP

Neighbor Discovery Protocol. Protocol used by IPv6 nodes on the same link to discover each other’s presence, determine each other’s link-layer addresses, find routers, and maintain reachability information about the paths to active neighbors. NDP is defined in RFC 2461 and is equivalent to the Address Resolution Protocol (ARP) used with IPv4. See also ARP.

neighbor

Adjacent system reachable by traversing a single subnetwork. An immediately adjacent router. Also called a peer.

NET

Network entity title. Network address defined by the ISO network architecture and used in CLNS-based networks.

NetBIOS

Network basic input/output system. An application programming interface (API) used by programs on a LAN. NetBIOS provides a uniform set of commands for requesting the lower-level services required to manage names, conduct sessions, and send datagrams between nodes on a network.

Network Address Port Translation

See NAPT.

Network Address Translation

See NAT.

network basic input/output system

See NetBIOS.

Network Control Protocol

See NCP.

network entity title

See NET.

network interface

Interface, such as an Ethernet or SONET/SDH interface, that primarily provides traffic connectivity. See also PIC and services interface.

network layer reachability information

See NLRI.

network link advertisement

OSPF link-state advertisement flooded throughout a single area by designated routers to describe all routers attached to the network.

network LSA

OSPF link-state advertisement sent by the designated router on a broadcast or NBMA segment. It advertises the subnet associated with the designated router’s segment.

network service access point

See NSAP.

network summary LSA

OSPF link-state advertisement sent by an ABR to advertise internal OSPF routing knowledge across an area boundary. See also ABR.

Network Time Protocol

See NTP.

NIC

Network Information Center. Internet authority responsible for assigning Internet-related numbers, such as IP addresses and autonomous system (AS) numbers. See also IANA.

NIST

National Institute of Standards and Technology. A nonregulatory U.S. federal agency whose mission is to develop and promote measurement, standards, and technology.

NLRI

Network layer reachability information. Information carried in BGP packets and used by MBGP.

nonclient peer

In a BGP route reflection, a BGP peer that is not a member of a cluster. See also client peer.

nonstop routing

See NSR.

notification cell

JUNOS software data structure generated by the Distribution Buffer Manager ASIC that represents the header contents of an IP packet. The Internet Processor ASIC uses the notification cell to perform a forwarding table lookup.

Notification message

BGP message that informs a neighbor about an error condition, and then in some cases terminates the BGP peering session.

not-so-stubby area

See NSSA.

NSAP

Network service access point. Connection to a network that is identified by a network address.

n-selector

Last byte of a nonclient peer address.

NSR

Nonstop routing. A high availability feature that allows a routing platform with redundant Routing Engines to preserve routing information on the backup Routing Engine and switch over from the primary Routing Engine to the backup Routing Engine without alerting peer nodes that a change has occurred. NSR uses the graceful Routing Engine switchover (GRES) infrastructure to preserve interface, kernel, and routing information.

NSSA

Not-so-stubby area. In OSPF, a type of stub area in which external routes can be flooded.

NTP

Network Time Protocol. A protocol used to synchronize computer clock times on a network.

Null Register message

PIM message sent by the first-hop router to the rendezvous point (RP). The message informs the RP that the local source is still actively sending multicast packets into the network. See also RP.

numeric range match conditions

Use of numeric values (protocol and port numbers) in the header of an IP packet to match criteria in a firewall filter.

O

Oakley

Key determination protocol based on the Diffie-Hellman algorithm that provides added security, including authentication. Oakley was the key-exchange algorithm mandated for use with the initial version of ISAKMP, although other algorithms can be used. Oakley describes a series of key exchanges called modes and details the services provided by each; for example, Perfect Forward Secrecy for keys, identity protection, and authentication. See also ISAKMP.

OAM

• Operation, Administration, and Maintenance. An ATM Forum specification for monitoring ATM virtual connections. OAM performs standard loopback, fault detection and notification, and remote defect identification for each connection, verifying that the connection is up and the router is operational. See also LFM.
• Operation, Administration, and Maintenance. A set of Ethernet connectivity specifications and functions providing connectivity monitoring, fault detection and notification, fault verification, fault isolation, loopback, and remote defect identification. The primary specifications defining Ethernet OAM are IEEE 902.3ah link-fault management (LFM) and IEEE 902.1ag Ethernet connectivity-fault management (CFM). See also CFM and LFM.

OC

Optical carrier. In SONET, the OC level indicates the transmission rate of digital signals on optical fiber.

OC12

SONET line with a transmission speed of 622 Mbps using fiber-optic cables.

OC3

SONET line with a transmission speed of 155.52 Mbps (payload of 150.336 Mbps) using fiber-optic cables. For SDH interfaces, OC3 is also known as STM1.

OIF

Outgoing interface. An interface used by multicast functions within a router to determine which egress ports to use for forwarding multicast groups.

OpenConfirm

BGP neighbor state that shows that a valid Open message was received from the remote peer.

Open message

BGP message that allows two neighbors to negotiate the parameters of the peering session.

OpenSent

BGP neighbor state that shows that an Open message was sent to the remote peer and the local router is waiting for an Open message to be returned.

Operation, Administration, and Maintenance

See OAM.

operational mode

JUNOS software mode that allows a user to view statistics and information about the router’s current operating status.

operation script

See op script.

op script

Operational script. Extensible Stylesheet Language for Transformations (XSLT) script written to automate network troubleshooting and network management. Op scripts can perform any function available through JUNOScript remote procedure calls (RPCs).

optical carrier

See OC.

origin

In BGP, an attribute that describes the source of the route.

orlonger

JUNOS software routing policy match type that represents all routes more specific than the given subnet, including the given subnet itself. It is similar to a mathematical greater-than-or-equal-to operation.

OSI

Open Systems Interconnection. Standard reference model for how messages are transmitted between two points on a network.

OSPF

Open Shortest Path First. A link-state IGP that makes routing decisions based on the shortest-path-first (SPF) algorithm (also referred to as the Dijkstra algorithm).

OSPF hello packet

Message sent by each OSPF router to each adjacent router. It is used to establish and maintain the router’s neighbor relationships.

outgoing interface

See OIF.

overlay network

Network design in which a logical Layer 3 topology (IP subnets) is operating over a logical Layer 2 topology (ATM PVCs). Layers in the network do not have knowledge of each other, and each layer requires separate management and operation.

oversubscription

Method that allows provisioning of more bandwidth than the line rate of the physical interface.

P

P2MP LSP

See point-to-multipoint LSP.

package

Collection of files that make up a JUNOS software component.

packet

Fundamental unit of information (message or fragment of a message) carried in a packet-switched network, for example, the Internet. See also PSN.

packet aging

Occurs when packets in the output buffer are overwritten by newly arriving packets. This happens because the available buffer size is greater than the available transmission bandwidth.

packet capture

Packet capture can be either of the following:

1. Packet sampling method, in which entire IPv4 packets flowing through a router are captured for analysis. Packets are captured in the Routing Engine and stored as libpcap-formatted files on the router. Packet capture files can be opened and analyzed offline with packet analyzers such as tcpdump or Ethereal. See also traffic sampling.
2. J-Web packet sampling method for quickly analyzing router control traffic destined for or originating from the Routing Engine. You can either decode and view the captured packets in the J-Web interface as they are captured, or save the packets to a file and analyze them offline with packet analyzers such as Ethereal. J-Web packet capture does not capture transient traffic.

packet classification

See classification.

packet data protocol

See PDP.

Packet Forwarding Engine

Portion of the router that processes packets by forwarding them between input and output interfaces.

packet loss priority

See PLP.

packet or cell switching

Transmission of packets from many sources over a switched network.

packet-switched network

See PSN.

PADI

PPPoE Active Discovery Initiation packet. A Point-to-Point Protocol over Ethernet (PPPoE) initiation packet that is broadcast by the client to start the discovery process.

PADO

PPPoE Active Discovery Offer packet. A Point-to-Point Protocol over Ethernet (PPPoE) offer packet that is sent to the client by one or more access concentrators in reply to a PPPoE Active Discovery Initiation (PADI) packet.

PADR

PPPoE Active Discovery Request packet. A Point-to-Point Protocol over Ethernet (PPPoE) packet sent by the client to one selected access concentrator to request a session.

PADS

PPPoE Active Discovery Session Confirmation packet. A Point-to-Point Protocol over Ethernet (PPPoE) packet sent by the selected access concentrator to confirm the session.

PADT

PPPoE Active Discovery Termination packet. A Point-to-Point Protocol over Ethernet (PPPoE) packet sent by either the client or the access concentrator to terminate a session.

partial sequence number PDU

See PSNP.

passive flow monitoring

Technique to intercept and observe specified data network traffic by using a routing platform such as a monitoring station that is not participating in the network.

path attribute

Information about a BGP route, such as the route origin, AS path, and next-hop router.

PathErr message

RSVP message indicating that an error has occurred along an established path LSP. The message is advertised upstream toward the ingress router and does not remove any RSVP soft state from the network.

PathTear message

RSVP message indicating that the established LSP and its associated soft state should be removed by the network. The message is advertised downstream hop by hop toward the egress router.

PBB

Provider backbone bridge. Defined in IEEE 802.1ah, PBBs offer a scalable solution for building large bridged networks by improving MAC address scalability and service instance scalability.

PBBN

Provider backbone bridge network. See PBB.

pcap

Software library for packet capturing. See also libpcap.

PC Card

(Previously known as a PCMCIA Card.) The removable storage media that ships with each router that contains a copy of the JUNOS software. The PC Card is based on standards published by the Personal Computer Memory Card International Association (PCMCIA).

PCI

Peripheral Component Interconnect. Standard, high-speed bus for connecting computer peripherals. Used on the Routing Engine.

PCI Express

Peripheral Component Interconnect Express. Next-generation, higher-bandwidth bus for connecting computer peripherals. A PCI Express bus uses point-to-point bus topology with a shared switch rather than the shared bus topology of a standard PCI bus. The shared switch on a PCI Express bus provides centralized traffic routing and management and can prioritize traffic. On some J-series Services Routers, PCI Express slots are backward compatible with PCI and can accept Physical Interface Modules (PIMs) intended for either PCI Express or PCI slots.

PCMCIA

Personal Computer Memory Card International Association. Industry group that promotes standards for credit card–size memory and I/O devices.

PDH

Plesiochronous Digital Hierarchy. Developed to carry digitized voice more efficiently. Evolved into the North America, European, and Japanese Digital Hierarchies, in which only a discrete set of fixed rates is available, namely, NxDS0 (DS0 is a 64-Kbps rate).

PDP

Packet data protocol. Network protocol, such as IP, used by packet data networks connected to a GPRS network.

PDU

Protocol data unit. A packet of data passed across a network. The term refers to a specific layer of the OSI seven-layer model and a specific protocol.

peak information rate

See PIR.

PEC

Policing equivalence classes. In traffic policing, a set of packets that are treated the same way by the packet classifier.

peer

Immediately adjacent router with which a protocol relationship has been established. Also called a neighbor.

peering

Practice of exchanging Internet traffic with directly connected peers according to commercial and contractual agreements.

PEM

Privacy Enhanced Mail. A technique for securely exchanging electronic mail over a public medium. Power Entry Module. Distributes DC power within the router chassis. Supported on M40e, M160, M320, and T-series routing platforms.

penultimate hop popping

See PHP.

penultimate router

Last transit router before the egress router in an MPLS label-switched path.

Perfect Forward Secrecy

See PFS.

Peripheral Component Interconnect

See PCI.

permanent interface

Interface that is always present in the routing platform. See also management Ethernet interface and transient interface.

permanent virtual circuit

See PVC.

PE router

Provider edge router. A router in the service provider’s network that is connected to a customer edge (CE) device and participates in a virtual private network (VPN).

persistent change

Commit script–generated configuration change that is copied to the candidate configuration. Persistent changes remain in the candidate configuration unless you explicitly delete them. See also transient change.

Personal Computer Memory Card International Association

See PCMCIA.

PFC

Protocol Field Compression. Normally, PPP-encapsulated packets are transmitted with a two-byte protocol field. For example, IPv4 packets are transmitted with the protocol field set to 0x0021, and MPLS packets are transmitted with the protocol field set to 0x0281. For all protocols with identifiers from 0x0000 through 0x00ff, PFC enables routers to compress the protocol field to one byte, as defined in RFC 1661, The Point-to-Point Protocol (PPP). PFC allows you to conserve bandwidth by transmitting less data. See also ACFC.

PFS

Perfect Forward Secrecy protocol. A protocol derived from an encryption system that changes encryption keys often and ensures that no two sets of keys have any relation to each other. If one set of keys is compromised, only communications using those keys are at risk. An example of a system that uses PFS is Diffie-Hellman.

PGM

Pragmatic General Multicast. A protocol layer that can be used between the IP layer and the multicast application on sources, receivers, and routers to add reliability, scalability, and efficiency to multicast networks.

PGP

Pretty Good Privacy. A strong cryptographic technique invented by Philip Zimmerman in 1991.

PHP

Penultimate hop popping. A mechanism used in an MPLS network that allows the transit router before the egress router to perform a label pop operation and forward the remaining data (often an IPv4 packet) to the egress router.

PHY

PHY can be either of the following:

1. Special electronic integrated circuit or functional block of a circuit that performs encoding and decoding between a pure digital domain (on-off) and a modulation in the analog domain. See also LAN PHY and WAN PHY.
2. Open Systems Interconnection (OSI) physical layer. Layer 1 of the OSI model that defines the physical link between devices.

physical interface

Port on a Physical Interface Card (PIC) or Physical Interface Module (PIM).

Physical Interface Card

See PIC.

Physical Interface Module

See multicast.

PIC

Physical Interface Card. A network interface–specific card that can be installed on an FPC in the router.

PIC I/O Manager ASIC

Juniper Networks ASIC responsible for receiving and transmitting information on the physical media. It performs media-specific tasks within the Packet Forwarding Engine.

PIM

PIM can be either of the following:

1. Protocol Independent Multicast. A protocol-independent multicast routing protocol. PIM dense mode is a flood-and-prune protocol. PIM sparse mode routes to multicast groups that use join messages to receive traffic. PIM sparse-dense mode allows some multicast groups to be dense groups (flood-and-prune) and some groups to be sparse groups (join and leave).
2. Physical Interface Module. A network interface card installed in a J-series Services Router to provide physical connections to a LAN or WAN. PIMs can be fixed or removable and interchangeable. The PIM receives incoming packets from the network and transmits outgoing packets to the network. Each PIM is equipped with a dedicated network processor that forwards incoming data packets to and receives outgoing data packets from the Routing Engine. During this process, the PIM performs framing and line-speed signaling for its medium type—for example, E1, serial, Fast Ethernet, or ISDN.

PIR

Peak information rate. The PIR must be equal to or greater than the CIR, and both must be configured to be greater than 0. Packets that exceed the PIR are marked red, which corresponds to high loss priority. See also CIR, trTCM.

PKI

Public key infrastructure. A hierarchy of trust that enables users of a public network to securely and privately exchange data through the use of public and private cryptographic key pairs that are obtained and shared with peers through a trusted authority.

Plesiochronous Digital Hierarchy

See PDH.

PLMN

Public Land Mobile Network. A telecommunications network for mobile stations.

PLP

Packet loss priority. Used to determine the random early detection (RED) drop profile when a packet is queued. You can set it by configuring a classifier or policer. The system supports two PLP designations: low and high.

PLP bit

Packet loss priority bit. Used to identify packets that have experienced congestion or are from a transmission that exceeded a service provider’s customer service license agreement. This bit can be used as part of a router’s congestion control mechanism and can be set by the interface or by a filter.

PLR

Point of local repair. The ingress router of a backup tunnel or a detour LSP.

point of local repair

See PLR.

Point of Presence

See POP.

point-to-multipoint connection

Unidirectional connection in which a single source system transmits data to multiple destination end systems. Point-to-multipoint is one of two fundamental connection types. See also point-to-point connection.

point-to-multipoint LSP

RSVP-signaled LSP with a single source and multiple destinations.

point-to-point connection

Unidirectional or bidirectional connection between two end systems. Point-to-point is one of two fundamental connection types. See also point-to-multipoint connection.

Point-to-Point Protocol

See PPP.

Point-To-Point Protocol process

See pppd.

poison reverse

Method used in distance-vector networks to avoid routing loops. Each router advertises routes back to the neighbor it received them from with an infinity metric assigned.

policer

Filter that limits traffic of a certain class to a specified bandwidth or burst size. Packets exceeding the policer limits are discarded, or assigned to a different forwarding class, a different loss priority, or both.

policing

Method of applying rate limits on bandwidth and burst size for traffic on a particular interface.

policing equivalence classes

See PEC.

policy chain

Application of multiple routing policies in a single location. The policies are evaluated in a predefined manner and are always followed by the default policy for the specific application location.

pop

Removal of the last label, by a router, from a packet as it exits an MPLS domain.

POP

Point of presence. A physical access point to the Internet. The location of the servers, routers, and ATM switches used to provide access to the Internet.

port mirroring

Method in which a copy of an IPv4 packet is sent from the routing platform to an external host address or a packet analyzer for analysis.

PPP

Point-to-Point Protocol. A link-layer protocol that provides multiprotocol encapsulation. PPP is used for link-layer and network-layer configuration. Provides a standard method for transporting multiprotocol datagrams over point-to-point links. Defined in RFC 1661.

pppd

Point-to-Point Protocol process (daemon) that processes packets that use PPP.

PPPoE

Point-to-Point Protocol over Ethernet. Network protocol that encapsulates PPP frames in Ethernet frames and connects multiple hosts over a simple bridging access device to a remote access concentrator.

PPPoE Active Discovery Initiation packet

See PADI.

PPPoE Active Discovery Offer packet

See PADO.

PPPoE Active Discovery Request packet

See PADR.

PPPoE Active Discovery Session Confirmation packet

See PADS.

PPPoE Active Discovery Termination packet

See PADT.

PPPoE over ATM

Point-to-Point Protocol over Ethernet frames in Asynchronous Transfer Mode. Network protocol that encapsulates Point-to-Point Protocol over Ethernet (PPPoE) frames in Asynchronous Transfer Mode (ATM) frames for digital subscriber line (DSL) transmission, and connects multiple hosts over a simple bridging access device to a remote access concentrator.

Pragmatic General Multicast

See PGM.

precedence bits

First three bits in the type-of-service (ToS) byte. On a Juniper Networks router, these bits are used to sort or classify individual packets as they arrive at an interface. The classification determines the queue to which the packet is directed upon transmission.

preference

Desirability of a route to become the active route. A route with a lower preference value is more likely to become the active route. The preference is an arbitrary value from 0 through 255 that the routing protocol process uses to rank routes received from different protocols, interfaces, or remote systems.

preferred address

On an interface, the default local address used for packets sourced by the local router to destinations on the subnet.

prefix-length-range

JUNOS software routing policy match type representing all routes that share the same most-significant bits. The prefix length of the route must also lie between the two supplied lengths in the route filter.

Pretty Good Privacy

See PGP.

primary address

On an interface, the address used by default as the local address for broadcast and multicast packets sourced locally and sent out the interface.

primary contributing route

Contributing route with the numerically smallest prefix and smallest JUNOS software preference value. This route is the default next hop used for a generated route.

primary interface

Router interface that packets go out on when no interface name is specified and when the destination address does not specify a particular outgoing interface.

Privacy Enhanced Mail

See PEM.

promiscuous mode

Used with ATM CCC Cell Relay encapsulation, enables mapping of all incoming cells from an interface port or from a virtual path (VP) to a single label-switched path (LSP) without restricting the VCI number.

Protected System Domain

A set of Flexible PIC Concentrators (FPCs) on a Juniper Networks routing platform matched with a redundant Routing Engine pair (or single Routing Engine) on the JCS 1200 platform to form a secure, virtual hardware router.

protocol address

Logical Layer 3 address assigned to an interface within the JUNOS software.

protocol data unit

See PDU.

protocol families

Grouping of logical properties within an interface configuration, for example, the inet, inet4, and mpls protocol families.

Protocol Field Compression

See PFC.

Protocol Independent Multicast

See multicast.

protocol preference

32-bit value assigned to all routes placed into the routing table. The protocol preference is used as a tiebreaker when multiple exact routes are placed into the table by different protocols.

provider backbone bridge

See PBB.

provider backbone bridge network

See PBBN.

provider edge router

See PE router.

provider router

Router in the service provider’s network that is not connected to a customer edge (CE) device.

Prune message

PIM message sent upstream to a multicast source or the rendezvous point (RP) of the domain. The message requests that multicast traffic stop being transmitted to the router originating the message.

PSD

See Protected System Domain.

PSN

Packet-switched network. Network in which messages or fragments of messages (packets) are sent to their destination through the most expedient route, as determined by a routing algorithm. Packet switching optimizes bandwidth in a network and minimizes latency.

PSNP

Partial sequence number PDU. A packet that contains only a partial list of the LSPs in the IS-IS link-state database.

public key infrastructure

See PKI.

Public Land Mobile Network

See PLMN.

push

Addition of a label or stack of labels, by a router, to a packet as it enters an MPLS domain.

PVC

Permanent virtual circuit. A software-defined logical connection in a network. See also SVC.

Q

Q-in-Q

See 802.1ad.

QoS

Quality of service. Performance, such as transmission rates and error rates, of a communications channel or system.

quad-wide

Type of PIC that combines the PIC and FPC within a single FPC slot.

qualified next hop

Next hop for a static route that allows a second next hop for the same static route to have different metric and preference properties from the original next hop.

quality of service

See QoS.

querier router

PIM router on a broadcast subnet responsible for generating IGMP query messages for the segment.

queue

First-in, first-out (FIFO) number of packets waiting to be forwarded over a router interface. You can configure the minimum and maximum size of the packet queue, queue admission policies, and other parameters to manage the flow of packets through the router.

queue fullness

For random early detection (RED), the memory used to store packets expressed as a percentage of the total memory allocated for that specific queue. See also drop profile.

queue length

For ATM1 interfaces only, a limit on the number of transmit packets that can be queued. Packets that exceed the limit are dropped. See also EPD.

queuing

In routing, the arrangement of packets waiting to be forwarded. Packets are organized into queues according to their priority, time of arrival, or other characteristics, and are processed one at a time. After a packet is sent to the outgoing interface on a router, it is queued for transmission on the physical media. The amount of time a packet is queued on the router is determined by the availability of the outgoing physical media, bandwidth, and the amount of traffic using the interface.

R

RA

Registration authority. A trusted third-party organization that acts on behalf of a certificate authority (CA) to verify the identity of a digital certificate user.

radio frequency interference

See RFI.

radio network controller

See RNC.

RADIUS

Remote Authentication Dial-In User Service. An authentication method for validating users who attempt to access the router using telnet.

random early detection

See RED.

Rapid Spanning Tree Protocol

See RSTP.

rate limiting

See policing.

RBOC

(Pronounced “are-bock”) Regional Bell operating company. Regional telephone companies formed as a result of the divestiture of the Bell System.

RC2, RC4, RC5

RSA codes. A family of proprietary (RSA Data Security, Inc.) encryption schemes often used in Web browsers and servers. These codes use variable-length keys up to 2048 bits.

RDBMS

Relational database management system. A system that presents data in a tabular form with a means of manipulating the tabular data with relational operators.

RDM

Russian-dolls bandwidth allocation model. An allocation model that makes efficient use of bandwidth by allowing the class types to share bandwidth. RDM is defined in the Internet draft draft-ietf-tewg-diff-te-russian-03.txt, Russian Dolls Bandwidth Constraints Model for Diff-Serv-aware MPLS Traffic Engineering.

Real-Time Performance Monitoring

See RPM.

Real-Time Transport Protocol

See RTP.

receive

Next hop for a static route that allows all matching packets to be sent to the Routing Engine for processing.

record route object

See RRO.

recursive lookup

Method of consulting the routing table to locate the actual physical next hop for a route when the supplied next hop is not directly connected.

RED

Random early detection. Gradual drop profile for a given class that is used for congestion avoidance. RED tries to anticipate incipient congestion by dropping a small percentage of packets from the head of the queue to ensure that a queue never actually becomes congested.

refresh reduction

In RSVP, an extension that addresses the problems of scaling, reliability, and latency when Refresh messages are used to cover message loss.

Regional Bell operating company

See RBOC.

Register message

PIM message unicast by the first-hop router to the rendezvous point (RP) that contains the multicast packets from the source encapsulated within its data field.

Register Stop message

PIM message sent by the RP to the first-hop router to halt the sending of encapsulated multicast packets.

registration authority

See RA.

reject

Next hop for a configured route that drops all matching packets from the network and returns an ICMP message to the source IP address. Also used as an action in a routing policy or firewall filter.

relational database management system

See RDBMS.

Remote Authentication Dial-In User Service

See RADIUS.

remote monitoring

See RMON.

remote procedure call

See RPC.

rename

JUNOS software command that allows a user to change the name of a routing policy, firewall filter, or any other variable character string defined in the router configuration.

rendezvous point

See RP.

Request for Comments

See RFC.

Request message

RIP message used by a router to ask for all or part of the routing table from a neighbor.

resolve

Next hop for a static route that allows the router to perform a recursive lookup to locate the physical next hop for the route.

Resource Reservation Protocol

See RSVP.

Response message

RIP message used to advertise routing information into a network.

result cell

JUNOS software data structure generated by the Internet Processor ASIC after performing a forwarding table lookup.

ResvConf message

RSVP message that allows the egress router to receive an explicit confirmation message from a neighbor that its Resv message was received.

ResvErr message

RSVP message indicating that an error has occurred along an established LSP. The message is advertised downstream toward the egress router, and it does not remove any RSVP soft state from the network.

ResvTear message

RSVP message indicating that the established LSP and its associated soft state should be removed by the network. The message is advertised upstream toward the ingress router.

reverse-path forwarding

See RPF.

reverse-path multicasting

See RPM.

revert timer

For SONET Automatic Protection Switching (APS), a timer that specifies the amount of time (in seconds) to wait after the working circuit has become functional before making the working circuit active again.

rewrite rules

Set the appropriate class-of-service (CoS) bits in an outgoing packet. This allows the next downstream router to classify the packet into the appropriate service group.

RFC

Request for Comments. Internet standard specifications published by the Internet Engineering Task Force (IETF).

RFI

Radio frequency interface. Interference from high-frequency electromagnetic waves emanating from electronic devices.

RIB

Routing information base. A logical data structure used by BGP to store routing information. See also routing table.

RID

Router ID. An IP address used by a router to uniquely identify itself to a routing protocol. This address may not be equal to a configured interface address.

RIP

Routing Information Protocol. Used in IPv4 networks, a distance-vector interior gateway protocol that makes routing decisions based on hop count.

RIPng

Routing Information Protocol next generation. Used in IPv6 networks, a distance-vector interior gateway protocol that makes routing decisions based on hop count.

RMON

Remote monitoring. A standard MIB that defines current and historical MAC-layer statistics and control objects, allowing you to capture real-time information across the entire network. This allows you to detect, isolate, diagnose, and report potential and actual network problems.

RNC

Radio network controller. Manages the radio part of the network in UMTS.

Root System Domain

Pair of redundant Routing Engines on a Juniper Networks routing platforms connected to the switch fabric on the Juniper Control System (JCS) platform. The configuration on the Routing Engines on the Juniper Networks routing platforms provides the RSD identification and the configuration of up to eight Protected System Domains (PSDs).

route distinguisher

6-byte value identifying a VPN that is prefixed to an IPv4 address to create a unique IPv4 address. The new address is part of the VPN IPv4 address family, which is a BGP address family added as an extension to the BGP protocol. It allows you to configure private addresses within the VPN by preventing overlap with the private addresses in other VPNs.

route filter

JUNOS software syntax used in a routing policy to match an individual route or a group of routes.

route flapping

Condition of network instability where a route is announced and withdrawn repeatedly, often as the result of an intermittently failing link.

route identifier

IP address of the router from which a BGP, IGP, or OSPF packet originated.

route redistribution

Method of placing learned routes from one protocol into another protocol operating on the same router. The JUNOS software accomplishes this with a routing policy.

route reflection

In BGP, the configuration of a group of routers into a cluster in which one system acts as a route reflector, redistributing routes from outside the cluster to all routers in the cluster. Routers in a cluster do not need to be fully meshed.

router ID

See RID.

router-link advertisement

OSPF link-state advertisement flooded throughout a single area by all routers to describe the state and cost of the router’s links to the area.

router LSA

OSPF link-state advertisement sent by each router in the network. It describes the local router’s connected subnets and their metric values.

router priority

Numerical value assigned to an OPSF or IS-IS interface that is used as the first criterion in electing the designated router or designated intermediate system, respectively.

routing domain

See AS.

Routing Engine

Portion of the router that handles all routing protocol processes, as well as other software processes that control the router’s interfaces, some of the chassis components, system management, and user access to the router.

routing gateway

A firewall, network address translation (NAT) router, or other routing device used as a customer premises (CPE) terminator in the home, office, or local point of presence (POP).

routing information base

See RIB.

Routing Information Protocol

See RIP.

Routing Information Protocol next generation

See RIPng.

routing instance

Collection of routing tables, interfaces, and routing protocol parameters. The set of interfaces is contained in the routing tables, and the routing protocol parameters control the information in the routing tables.

routing matrix

Terabit routing system interconnecting up to four T640 routing nodes and a TX Matrix platform to deliver up to 2.56 terabits per second (Tbps) of subscriber switching capacity.

routing plane

Used to describe the interconnected routing engines within a routing matrix. There are two routing planes, the master routing plane, which includes all master Routing Engines, and the backup routing plane, which includes all backup routing planes.

routing protocol daemon

See rpd.

routing table

Common database of routes learned from one or more routing protocols. All routes are maintained by the JUNOS routing protocol process.

RP

Rendezvous point. For PIM sparse mode, a core router acting as the root of the distribution tree in a shared tree.

RPC

Remote procedure call. A type of protocol that allows a computer program running on one computer to cause a function on another computer to be executed without explicitly coding the details for this interaction.

rpd

JUNOS software routing protocol process (daemon). A user-level background process responsible for starting, managing, and stopping the routing protocols on a Juniper Networks router.

RPF

Reverse path forwarding. An algorithm that checks the unicast routing table to determine whether there is a shortest path back to the source address of the incoming multicast packet. Unicast RPF helps determine the source of denial-of-service attacks and rejects packets from unexpected source addresses.

RPM

RPM can be either of the following:

• Reverse-path multicasting. Routing algorithm used by Distance Vector Multicast Routing Protocol (DVMRP) to forward multicast traffic.
• Real-Time Performance Monitoring. A tool for creating active probes to track and monitor traffic.

RRO

Record route object. An RSVP message object that notes the IP address of each router along the path of an LSP.

RSA codes

See RC2, RC4, RC5.

RSD

See Root System Domain.

RSTP

Rapid Spanning Tree Protocol. A spanning-tree protocol used to prevent loops in bridge configurations. RSTP is not aware of VLANs and blocks ports at the physical level. See also MSTP.

RSVP

Resource Reservation Protocol. A signaling protocol that establishes a session between two routers to transport a specific traffic flow.

RSVP Path message

RSVP message sent by the ingress router downstream toward the egress router. It begins the establishment of a soft state database for a particular label-switched path.

RSVP Resv message

RSVP message sent by the egress router upstream toward the ingress router. It completes the establishment of the soft state database for a particular label-switched path.

RSVP signaled LSP

Label-switched path that is dynamically established using RSVP Path and Resv messages.

RSVP-TE

RSVP-traffic engineering; RSVP with traffic engineering extensions as defined by RFC 3209. These extensions allow RSVP to establish label-switched paths (LSPs) in MPLS networks. See also MPLS, RSVP.

RTP

Real-Time Transport Protocol. An Internet protocol that provides mechanisms for the transmission of real-time data, such as audio, video, or voice, over IP networks. Compressed RTP is used for VoIP traffic.

RTVBR

Real-time variable bit rate. For ATM2 intelligent queuing (IQ) interfaces, data that is serviced at a higher priority rate than other VBR data. RTVBR is suitable for carrying packetized video and audio. RTVBR provides better congestion control and latency guarantees than non-real-time VBR.

S

S/T interface

System reference point/terminal reference point interface. A four-pair connection between the ISDN provider service and the customer terminal equipment.

SA

Security association. An IPsec term that describes an agreement between two parties about what rules to use for authentication and encryption algorithms, key exchange mechanisms, and secure communications.

sampling

Method where the sampling key based on the IPv4 header is sent to the Routing Engine. There, the key is placed in a file, or cflowd packets based on the key are sent to a cflowd server.

SAP

SAP can be either of the following:

1. Session Announcement Protocol. Used with multicast protocols to handle session conference announcements.
2. Service access point. Device that identifies routing protocols and provides the connection between the network interface card and the rest of the network.

SAR

Segmentation and reassembly. Buffering used with ATM.

SCB

System Control Board. On an M40 router, the part of the Packet Forwarding Engine that performs route lookups, monitors system components, and controls FPC resets.

SCC

Switch-card chassis. Term used by the JUNOS command-line interface (CLI) to refer to the TX Matrix platform in a routing matrix.

SCEP

Simple Certificate Enrollment Protocol. A protocol for digital certificates that supports certificate authority (CA) and registration authority (RA) public key distribution, certificate enrollment, certificate revocation, certificate queries, and certificate revocation list (CRL) queries.

SCG

SONET Clock Generator. On a T640 routing node, provides the Stratum 3 clock signal for the SONET/SDH interfaces. Also provides external clock inputs.

scheduler maps

In class of service, schedule maps associate schedulers with specific forwarding classes. See also schedulers, forwarding classes.

schedulers

Define the priority, bandwidth, delay buffer size, rate control status, and RED drop profiles of a packet transmission. Schedulers are mapped to a specific forwarding class by a scheduler map. See also scheduler maps.

scheduling

Method of determining which type of packet or queue is transmitted before another. An individual router interface can have multiple queues assigned to store packets. The router then determines which queue to service based on a particular method of scheduling. This process often involves a determination of which type of packet should be transmitted before another. For example, first in, first out (FIFO). See also FIFO.

scp

Secure copy. Means of securely transferring computer files between a local and remote host or between two remote hosts, using the Secure Shell (SSH) protocol.

SCU

Source class usage. A means of tracking traffic originating from specific prefixes on the provider core router and destined for specific prefixes on the customer edge router, based on the IP source and destination addresses.

SDH

Synchronous Digital Hierarchy. A CCITT variation of the SONET standard.

SDP

Session Description Protocol. Used with multicast protocols to handle session conference announcements.

SDRAM

Synchronous dynamic random-access memory. An electronic standard in which the inputs and outputs of SDRAM data are synchronized to an externally supplied clock, allowing for extremely fast consecutive read and write capacity.

SDX software

Service Deployment System software. Depricated term. See SRC software.

secure copy

See SCP.

Secure Hash Algorithm

See SHA-1.

Secure Shell

See SSH.

Secure Shell with Transport Layer Security

See SSH/TLS.

Secure Sockets Layer

See SSL.

security association

See SA.

Security Parameter Index

See SPI.

segmentation and reassembly

See SAR.

serial interface

DTE/DCE interface for WAN links. See also DTE and DCE.

service access point

See SAP.

Service Deployment System software

See SRX software.

Service Profile Identifier

See SPID.

services interface

Interface that provides specific capabilities for manipulating traffic before it is delivered to its destination, for example, the adaptive services interface and the tunnel services interface. See also network interface.

Serving GPRS Support Node

See SGSN.

Session and Resource Control software

See SRX software.

Session Announcement Protocol

See SAP.

session attribute object

RSVP message object used to control the priority, preemption, affinity class, and local rerouting of the LSP.

Session Description Protocol

See SDP.

Session Initiation Protocol

See SIP.

set-top box

The end host or device used to receive IPTV video streams.

SFM

Switching and Forwarding Module. On an M160 router, a component of the Packet Forwarding Engine that provides route lookup, filtering, and switching to FPCs.

SFP

Small form-factor pluggable transceiver. A transceiver that provides support for optical or copper cables. SFPs are hot-insertable and hot-removable. See also XFP.

SGSN

Serving GPRS Support Node. Device in the mobile network that requests PDP contexts with a GGSN.

SHA-1

Secure Hash Algorithm 1. A secure hash algorithm standard defined in FIPS PUB 180-1 (SHA-1). Developed by the National Institute of Standards and Technology (NIST), SHA-1 (which effectively replaces SHA-0) produces a 160-bit hash for message authentication. Longer-hash variants include SHA-224, SHA-256, SHA-384, and SHA-512 (sometimes grouped under the name “SHA-2”). SHA-1 is more secure than MD5. See also hashing, MD5.

sham link

Unnumbered point-to-point intra-area link advertised by a type 1 link-state advertisement (LSA).

shaping rate

In class of service, controls the maximum rate of traffic transmitted on an interface. See also traffic shaping.

shared scheduling and shaping

Allocation of separate pools of shared resources to subsets of logical interfaces belonging to the same physical port.

shared tree

Multicast forwarding tree established from the rendezvous point (RP) to the last-hop router for a particular group address.

SHDSL

Symmetric high-speed digital subscriber line. A standardized multirate symmetric DSL that transports rate-adaptive symmetrical data across a single copper pair at data rates from 192 Kbps to 2.3 Mbps, or from 384 Kbps to 4.6 Mbps over two pairs, covering applications served by HDSL, SDSL, T1, E1, and services beyond E1. SHDSL conforms to the following recommendations: ITU G.991.2 G.SHDSL, ETSI TS 101-524 SDSL, and the ANSI T1E1.4/2001-174 G.SHDSL. See also G.SHDSL.

SHDSL transceiver unit-central office

See STU-C.

SHDSL transceiver unit-remote

See STU-R.

shim header

Location of the MPLS header in a data packet. The JUNOS software always places (shims) the header between the existing Layer 2 and Layer 3 headers.

shortest path first

See SPF.

shortest-path tree

See SPT.

short message service

See SMS.

SIB

Switch Interface Board. On a T640 routing node, provides the switching function to the destination Packet Forwarding Engine.

signaled path

In traffic engineering, an explicit path; that is, a path determined using RSVP signaling. The Explicit Route Object carried in the packets contains the explicit path information.

Signaling System 7

See SS7.

Simple Certificate Enrollment Protocol

See SCEP.

Simple Network Management Protocol

See SNMP.

simplex interface

Interface that treats packets it receives from itself as the result of a software loopback process. The interface does not consider these packets when determining whether the interface is functional.

single-mode fiber

Optical fiber designed for transmission of a single ray or mode of light as a carrier and used for long-distance signal transmission. For short distances, multimode fiber is used. See also MMF.

SIP

Session Initiation Protocol. An adaptive services application protocol option used for setting up sessions between endpoints on the Internet. Examples include telephony, fax, videoconferencing, file exchange, and person-to-person sessions.

small form-factor pluggable transceiver

See SFP.

SMS

Short message service. A GSM service that enables short text messages to be sent to and from mobile telephones.

SNA

System Network Architecture. IBM proprietary networking architecture consisting of a protocol stack that is used primarily in banks and other financial transaction networks.

SNMP

Simple Network Management Protocol. A protocol governing network management and the monitoring of network devices and their functions.

soft state

In RSVP, control state in hosts and routers that expires if not refreshed within a specified amount of time.

SONET

Synchronous Optical Network. A high-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS1 is the basic building block of SONET. Approved as an international standard in 1988. See also SDH.

SONET Clock Generator

See SCG.

source-based tree

Multicast forwarding tree established from the source of traffic to all interested receivers for a particular group address. It is often used in a dense-mode forwarding environment.

source class usage

See SCU.

source service access point

See SSAP.

source-specific multicast

See SSM.

Spanning Tree Protocol

See STP.

sparse mode

Method of operating a multicast domain where sources of traffic and interested receivers meet at a central rendezvous point. A sparse-mode network assumes that there are very few receivers for each group address.

SPF

Shortest path first. An algorithm used by IS-IS and OSPF to make routing decisions based on the state of network links. Also called the Dijkstra algorithm.

SPI

Security Parameter Index. In IPsec, a numeric identifier used with the destination address and security protocol to identify an SA. When IKE is used to establish an SA, the SPI is randomly derived. When manual configuration is used for an SA, the SPI must be entered as a parameter.

SPID

Service Profile Identifier. Used only in Basic Rate Interface (BRI) implementations of ISDN. The SPID specifies the services available on the service provider switch and defines the feature set ordered when the ISDN service is provisioned.

split horizon

Method used in distance-vector networks to avoid routing loops. Each router does not advertise routes back to the neighbor from which it received them.

SPQ

Strict-priority queuing. A dequeuing method that provides a special queue that is serviced until it is empty. The traffic sent to this queue tends to maintain a lower latency and more consistent latency numbers than traffic sent to other queues. See also APQ.

SPT

Shortest-path tree. An algorithm that builds a network topology that attempts to minimize the path from one router (the root) to other routers in a routing area.

SQL

Structured query language. International standard language used to create, modify, and select data from relational databases.

src port

TCP or UDP port for the source IP address in a packet.

SRX software

Session and Resource Control software. Customizable Juniper Networks product with which service providers can rapidly deploy IP services—such as video on demand (VoD), IP television, stateful firewalls, Layer 3 VPNs, and bandwidth on demand (BoD)—to hundreds of thousands of subscribers over a variety of broadband access technologies. Formerly known as Service Deployment System software.

SS7

Signaling System 7. A protocol used in telecommunications for delivering calls and services.

SSAP

Source service access point. Device that identifies the origin of an LPDU on a DLSw network.

SSB

System and Switch Board. On an M20 router, a Packet Forwarding Engine component that performs route lookups and component monitoring and monitors FPC operation.

SSH

Secure Shell. A protocol that uses strong authentication and encryption for remote access across a nonsecure network. SSH provides remote login, remote program execution, file copy, and other functions. In a UNIX environment, SSH is intended as a secure replacement for rlogin, rsh, and rcp.

SSH/TLS

Secure Shell with Transport Layer Security. A combination of two standard methods used to secure communications over the Internet. TLS is the name of a standard protocol based on SSL 3.0 and is defined in RFC 2246. In combination, SSH/TLS is also known as SSHv2 and uses FIPS-restricted cipher sets in a FIPS environment.

SSL

Secure Sockets Layer. A protocol that encrypts security information using public-private key technology, which requires a paired private key and authentication certificate, before transmitting data across a network.

SSM

Source-specific multicast. A service that allows a client to receive multicast traffic directly from the source. Typically, SSM uses a subset of the PIM sparse-mode functionality along with a subset of IGMPv3 to create a shortest-path tree between the client and the source, but it builds the shortest-path tree without the help of a rendezvous point.

SSP

Switch-to-Switch Protocol. Protocol implemented between two DLSw routers that establishes connections, locates resources, forwards data, and handles error recovery and flow control.

SSRAM

Synchronous static random-access memory. Used for storing routing tables, packet pointers, and other data such as route lookups, policer counters, and other statistics to which the microprocessor needs quick access.

S-TAG

Field defined in the IEEE 802.1ad Q-in-Q encapsulation header that carries the S-VLAN identifier information. See also B-TAG.

S-tagged service interface

Interface between a customer edge (CE) device and the I-BEB or IB-BEB network components. Frames passed through this interface contain an S-TAG field. See also B-tagged service interface.

standard AAL5 mode

Transport mode that allows multiple applications to tunnel the protocol data units of their Layer 2 protocols over an ATM virtual circuit. You use this transport mode to tunnel IP packets over an ATM backbone. See also AAL5 mode, cell-relay mode, Layer 2 circuits, trunk mode.

starvation

Problem that occurs when lower-priority traffic, such as data and protocol packets, is locked out (starved) because a higher-priority queue uses all of the available transmission bandwidth.

stateful firewall

See stateful firewall filter and stateless firewall filter.

stateful firewall filter

Type of firewall filter that evaluates the context of connections, permits or denies traffic based on the context, and updates this information dynamically. Context includes IP source and destination addresses, port numbers, TCP sequencing information, and TCP connection flags. The context established in the first packet of a TCP session must match the context contained in all subsequent packets if a session is to remain active. See also stateless firewall filter.

stateful firewall recovery

Recovery strategy that preserves parameters concerning the history of connections, sessions, or application status before failure. See also stateless firewall recovery.

stateless firewall filter

Type of firewall filter that statically evaluates the contents of packets transiting the router and packets originating from or destined for the Routing Engine. Packets are accepted, rejected, forwarded, or discarded and collected, logged, sampled, or subjected to classification according to a wide variety of packet characteristics. Sometimes called access control lists (ACLs) or simply firewall filters, stateless firewall filters protect the processes and resources owned by the Routing Engine. A stateless firewall filter can evaluate every packet, including fragmented packets. In contrast to a stateful firewall filter, a stateless firewall filter does not maintain information about connection states. See also stateful firewall filter.

stateless firewall recovery

Recovery strategy that does not attempt to preserve the history of connections, sessions, or application status before failure. See also stateful firewall recovery.

static LSP

See static path.

static path

In the context of traffic engineering, a static route that requires hop-by-hop manual configuration. No signaling is used to create or maintain the path. Also called a static LSP.

static route

Explicitly configured route that is entered into the routing table. Static routes have precedence over routes chosen by dynamic routing protocols.

static RP

One of three methods of learning the rendezvous point (RP) to group address mapping in a multicast network. Each router in the domain must be configured with the required RP information.

STM

Synchronous transport module. CCITT specification for SONET at 155.52 Mbps.

STP

Spanning Tree Protocol. Defined in the IEEE standard 802.1D, the Spanning Tree Protocol is an OSI Layer 2 protocol that ensures a loop-free topology for any bridged LAN. This protocol creates a spanning tree within a mesh network of connected Layer 2 bridges (typically Ethernet switches), and disables the links that are not part of that tree, leaving a single active path between any two network nodes.

strict

In the context of traffic engineering, a route that must go directly to the next address in the path. (Definition from RFC 791, modified to fit LSPs.)

strict hop

Routers in an MPLS named path that must be directly connected to the previous router in the configured path.

strict–priority queue

See SPQ.

structured query language

See SQL.

STS

Synchronous transport signal. Synchronous transport signal level 1 is the basic building block signal of SONET, operating at 51.84 Mbps. Faster SONET rates are defined as STS-n, where n is an integer by which the basic rate of 51.84 Mbps is multiplied. See also SONET.

stub area

In OSPF, an area through which, or into which, AS external advertisements are not flooded.

STU-C

Symmetric high-speed digital subscriber line (SHDSL) transceiver unit–central office. Equipment at the telephone company central office that provides SHDSL connections to remote user terminals.

STU-R

Symmetric high-speed digital subscriber line (SHDSL) transceiver unit–remote. Equipment at the customer premises that provides SHDSL connections to remote user terminals.

sub-LSP

Part of a point-to-multipoint label-switched-path (LSP). A sub-LSP carries traffic from the main LSP to one of the egress PE routers. Each point-to-multipoint LSP has multiple sub-LSPs. See also point-to-multipoint LSP.

subnet mask

Number of bits of the network address used for the host portion of a Class A, Class B, or Class C IP address.

subrate value

Value that reduces the maximum allowable peak rate by limiting the HDLC-encapsulated payload. The subrate value must exactly match that of the remote channel service unit (CSU).

summary link advertisement

OSPF link-statement advertisement flooded throughout the advertisement’s associated areas by area border routers to describe the routes that they know about in other areas.

SVC

Switched virtual connection. A dynamically established, software-defined logical connection that stays up as long as data is being transmitted. When transmission is complete, the software tears down the SVC. See also PVC.

S-VLAN

Specific service instance VLAN identifier carried inside the S-TAG field. See also B-VID.

switch

A network device that attempts to perform as much of the forwarding task in hardware as possible. The switch can function as a bridge (LAN switch), router, or some other specialized device, and forwards frames, packets, or other data units. See also bridge.

switch-card chassis

See SCC.

switched virtual connection

See SVC.

Switching and Forwarding Module

See SFM.

Switch Interface Board

See SIB.

Switch-to-Switch Protocol

See SSP.

symmetric high-speed digital subscriber line

See SHDSL.

Synchronous Digital Hierarchy

See SDH.

synchronous dynamic random-access memory

See SDRAM.

Synchronous Optical Network

See SONET.

synchronous static random-access memory

See SSRAM.

synchronous transport module

See STM.

synchronous transport signal

See STS.

sysid

System identifier. Portion of the ISO nonclient peer. The system ID can be any 6 bytes that are unique throughout a domain.

syslog

System log. A method for storing messages to a file for troubleshooting or record-keeping. It can also be used as an action within a firewall filter to store information to the messages file.

System and Switch Board

See SSB.

System Control Board

See SCB.

system ID

See sysid.

system log

See syslog.

System Network Architecture

See SNA.

T

T1

Basic physical layer protocol used by the Digital Signal level 1 (DS1) multiplexing method in North America. A T1 interface operates at a bit rate of 1.544 Mbps and can support 24 DS0 channels.

T3

Physical layer protocol used by the Digital Signal level 3 (DS3) multiplexing method in North America. A T3 interface operates at a bit rate of 44.736 Mbps.

TACACS+

Terminal Access Controller Access Control System Plus. Authentication method for validating users who attempt to access the router using telnet.

tail drop

Queue management algorithm for dropping packets from the input end (tail) of the queue when the length of the queue exceeds a configured threshold. See also RED.

T-carrier

Generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan.

TCM

Tricolor marking. Traffic policing mechanism that extends the functionality of class-of-service (CoS) traffic policing by providing three levels of drop precedence (loss priority or PLP) instead of two. There are two types of TCM: single-rate and two-rate. The JUNOS software currently supports two-rate TCM only. See also trTCM.

TCP

Transmission Control Protocol. Works in conjunction with the Internet Protocol (IP) to send data over the Internet. Divides a message into packets and tracks the packets from point of origin to destination.

tcpdump

UNIX packet monitoring utility used by the JUNOS software to view information about packets sent or received by the Routing Engine.

TCP port 179

Well-known port number used by BGP to establish a peering session with a neighbor.

TDMA

Time-Division Multiple Access. A type of multiplexing in which two or more channels of information are transmitted over the same link, where the channels take turns to use the link. Each link is allocated a different time interval (“slot” or “slice”) for the transmission of each channel. For the receiver to distinguish one channel from the other, some kind of periodic synchronizing signal or distinguishing identifier is required. See also GSM.

TEI

Terminal Endpoint Identifier. A terminal endpoint can be any ISDN-capable device attached to an ISDN network. The TEI is a number between 0 and 127, where 0 through 63 are used for static TEI assignment, 64 through 126 are used for dynamic assignment, and 127 is used for group assignment.

Terminal Access Controller Access Control System Plus

See TACACS+.

Terminal Endpoint Identifier

See TEI.

terminating action

Action in a routing policy or firewall filter that halts the logical software processing of a policy or filter.

terms

Used in a routing policy or firewall filter to segment the policy or filter into small match and action pairs.

Third-Generation Partnership Project

See 3GPP.

through

JUNOS software routing policy match type representing all routes that fall between the two supplied prefixes in the route filter.

Time-Division Multiple Access

See TDMA.

time-division multiplexed channel

Channel derived from a given frequency and transmitted over a single wire or wireless medium. The channel is preassigned a time slot whether or not there is data to transmit.

timeout timer

Used in a distance-vector protocol to ensure that the current route is still usable for forwarding traffic.

TNP

Trivial Network Protocol. A Juniper Networks proprietary protocol automatically configured on an internal interface by the JUNOS software. TNP is used to communicate between the Routing Engine and components of the Packet Forwarding Engine, and is critical to the operation of the router.

token-bucket algorithm

Used in a rate-policing application to enforce an average bandwidth while allowing bursts of traffic up to a configured maximum value.

ToS

Type of service. The method of handling traffic using information extracted from the fields in the ToS byte to differentiate packet flows.

totally stubby area

OSPF area type that prevents Type 3, 4, and 5 link-state advertisements (LSAs) from entering the nonbackbone area.

traffic engineering

Process of selecting the paths chosen by data traffic in order to balance the traffic load on the various links, routers, and switches in the network. (Definition from http://www.ietf.org/internet-drafts/draft-ietf-mpls-framework-04.txt.) See also MPLS.

traffic engineering class

In Differentiated Services–aware traffic engineering, a paired class type and priority.

traffic engineering class map

In Differentiated Services–aware traffic engineering, a map among the class types, priorities, and traffic engineering classes. The traffic engineering class mapping must be consistent across the Differentiated Services domain.

traffic policing

Examines traffic flows and discards or marks packets that exceed service-level agreements (SLAs).

traffic sampling

Method used to capture individual packet information of traffic flow at a specified time period. The sampled traffic information is placed in a file and stored on a server for various types of analysis. See also packet capture.

traffic shaping

Reduces the potential for network congestion by placing packets in a queue with a shaper at the head of the queue. Traffic shaping tools regulate the rate and volume of traffic admitted to the network. See also shaping rate.

transient change

Commit script–generated configuration change that is loaded into the checkout configuration, but not into the candidate configuration. Transient changes are not saved in the configuration if the associated commit script is deleted or deactivated. See also persistent change.

transient interface

Interface that can be configured on a routing platform depending on your network needs. Unlike a permanent interface that is required for router operation, a transient interface can be disabled or removed without affecting basic operation of the router. See also FPC, PIC, and permanent interface.

transit area

In OSPF, an area used to pass traffic from one adjacent area to the backbone, or to another area if the backbone is more than two hops away from an area.

transit router

In MPLS, any intermediate router in the LSP between the ingress router and the egress router.

Transmission Control Protocol

See TCP.

transport mode

IPsec mode of operation in which the data payload is encrypted, but the original IP header is left untouched. The IP addresses of the source or destination can be modified if the packet is intercepted. Because of its construction, transport mode can be used only when the communication endpoint and cryptographic endpoint are the same. VPN gateways that provide encryption and decryption services for protected hosts cannot use transport mode for protected VPN communications. See also tunnel mode.

transport plane

See data plane.

trap

Reports significant events occurring on a network device, most often errors or failures. SNMP traps are defined in either standard or enterprise-specific MIBs.

tricolor marking

See TCM.

triggered updates

Used in a distance-vector protocol to reduce the time for the network to converge. When a router has a topology change, it immediately sends the information to its neighbors instead of waiting for a timer to expire.

Triple Data Encryption Standard

See 3DES.

Trivial Network Protocol

See TNP.

trTCM

Two-rate TCM polices traffic according to the color classification (loss priority) of each packet. Traffic policing is based on two rates: the committed information rate (CIR) and the peak information rate (PIR). Two-rate TCM is defined in RFC 2698, A Two Rate Three Color Marker. See also CIR, PIR.

trunk mode

Layer 2 circuit cell-relay transport mode that allows you to send ATM cells between ATM2 IQ interfaces over an MPLS core network. You use Layer 2 circuit trunk mode (as opposed to standard Layer 2 circuit cell-relay mode) to transport ATM cells over an MPLS core network that is implemented between other vendors’ switches or routers. The multiple connections associated with a trunk increase bandwidth and provide failover redundancy. See also AAL5 mode, cell-relay mode, Layer 2 circuits, standard AAL5 mode.

Tspec object

RSVP message object that contains information such as the bandwidth request of the LSP as well as the minimum and maximum packets supported.

tunnel

Private, secure path through an otherwise public network.

tunnel endpoint

Last node of a tunnel where the tunnel-related headers are removed from the packet, which is then passed on to the destination network.

tunneling protocol

Network protocol that encapsulates one protocol or session inside another. When protocol A is encapsulated within protocol B, A treats B as though it were a data-link layer. Tunneling can be used to transport a network protocol through a network that would not otherwise support it. Tunneling can also be used to provide various types of VPN functionality such as private addressing.

tunnel mode

IPsec mode of operation in which the entire IP packet, including the header, is encrypted and authenticated and a new VPN header is added, protecting the entire original packet. This mode can be used by both VPN clients and VPN gateways, and protects communications that come from or go to non-IPsec systems. See also transport mode.

tunnel services interface

Provides the capability of a Tunnel Services PIC on an AS PIC. See Tunnel Services PIC.

Tunnel Services PIC

Physical interface card that allows the router to perform the encapsulation and de-encapsulation of IP datagrams. The Tunnel Services PIC supports IP-IP, GRE, and PIM register encapsulation and de-encapsulation. When the Tunnel Services PIC is installed, the router can be a PIM rendezvous point (RP) or a PIM first-hop router for a source that is directly connected to the router.

two-rate TCM

See trTCM.

TX Matrix platform

Routing platform that provides the centralized switching fabric of the routing matrix.

type of service

See ToS.

U

UDP

User Datagram Protocol. In TCP/IP, a connectionless transport layer protocol that exchanges datagrams without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols.

U interface

User reference point interface. A single-pair connection between the local ISDN provider and the customer premises equipment.

UME

UNI management entity. The code residing in the ATM devices at each end of a UNI (user-to-network interface) circuit that functions as an SNMP agent, maintaining network and connection information specified in a MIB.

UMTS

Universal mobile telecommunications system. Provides third-generation (3G), packet-based transmission of text, digitized voice, video, and multimedia, at data rates up to 2 Mbps.

UMTS Terrestrial Radio Access Network

See UTRAN.

UNI

User-to-network interface. ATM Forum specification that defines an interoperability standard for the interface between a router or an ATM switch located in a private network and the ATM switches located within the public carrier networks. Also used to describe similar connections in Frame Relay networks.

unicast

Operation of sending network traffic from one network node to another individual network node.

UNI management entity

See UME.

uninterruptible power supply

See UPS.

unit

JUNOS software syntax that represents the logical properties of an interface.

universal mobile telecommunications system

See UMTS.

unnumbered interface

Logical interface that is configured without an IP address.

Update message

BGP message that advertises path attributes and routing knowledge to an established neighbor.

update timer

Used in a distance-vector protocol to advertise routes to a neighbor on a regular basis.

UPS

Uninterruptible power supply. A device that sits between a power supply and a router or other device and prevents power-source events, such as outages and surges, from affecting or damaging the device.

upto

JUNOS software routing policy match type representing all routes that share the same most-significant bits and whose prefix length is smaller than the supplied subnet in the route filter.

User Datagram Protocol

See UDP.

UTC

Coordinated Universal Time. Historically referred to as Greenwich mean time (GMT), a high-precision atomic time standard that tracks Universal Time (UT) and is the basis for legal civil time all over the Earth. Time zones around the world are expressed as positive and negative offsets from UTC.

UTRAN

UMTS Terrestrial Radio Access Network. The WCDMA radio network in UMTS.

V

vapor corrosion inhibitor

See VCI.

variable bit rate

See VBR.

VBR

Variable bit rate. For ATM1 and ATM2 intelligent queuing (IQ) interfaces, data that is serviced at a varied rate within defined limits. VBR traffic adds the ability to statistically oversubscribe user traffic.

VC

Virtual circuit. A software-defined logical connection between two network devices that is not a dedicated connection but acts as though it is. It can be either permanent (PVC) or switched (SVC). VCs are used in ATM, Frame Relay, and X.25. See also VPI, VCI, PVC, SVC.

VCI

VCI can be either of the following:

1. Vapor corrosion inhibitor. Small cylinder packed with the router that prevents corrosion of the chassis and components during shipment.
2. Virtual circuit identifier. A 16-bit field in the header of an ATM cell that indicates the particular virtual circuit the cell takes through a virtual path. Also called a logical interface. See also VPI.

video on demand

See VOD.

video services router

See VSR.

virtual channel

Enables queuing, packet scheduling, and accounting rules to be applied to one or more logical interfaces. See also virtual channel group.

virtual channel group

Combines virtual channels into a group and then applies the group to one or more logical interfaces. See also virtual channel.

virtual circuit

Represents a logical connection between two Layer 2 devices in a network.

virtual circuit identifier

See VCI.

virtual connection

See VC.

virtual link

In OSPF, a link created between two routers that are part of the backbone but are not physically contiguous.

virtual local area network

See VLAN.

virtual loopback tunnel interface

See VT.

virtual path

Combination of multiple virtual circuits between two devices in an ATM network.

virtual path identifier

See VPI.

virtual private network

See VPN.

Virtual Router Redundancy Protocol

See VRRP.

virtual switch

A routing instance that can contain one or more bridge domains.

VLAN

Virtual local area network. A logical group of network devices that appear to be on the same LAN, regardless of their physical location. VLANs are configured with management software, and are extremely flexible because they are based on logical, rather than physical, connections.

VLANs span one or more ports on multiple devices. By default, each VLAN maintains its own Layer 2 forwarding database containing MAC addresses learned from packets received on ports belonging to the VLAN. See also bridge domain.

VLAN-tagged frame

Tagged frame whose tag header carries both VLAN identification and priority information.

VOD

Video on demand. A unicast streaming video offering by service providers that enables the reception of an isolated video session per user with rewind, pause, and similar VCR-like capabilities.

VPI

Virtual path identifier. An 8-bit field in the header of an ATM cell that indicates the virtual path the cell takes. See also VCI.

VPLS

Virtual private LAN service. An Ethernet-based multipoint-to-multipoint Layer 2 VPN service used for interconnecting multiple Ethernet LANs across an MPLS backbone. VPLS is specified in the IETF draft Virtual Private LAN Service.

VPN

Virtual private network. A private data network that uses a public TCP/IP network, typically the Internet, while maintaining privacy with a tunneling protocol, encryption, and security procedures. See also tunneling protocol.

VRF instance

VPN routing and forwarding instance. A VRF instance for a Layer 3 VPN implementation consists of one or more routing tables, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of policies and routing protocols that determine what goes into the forwarding table.

VRF table

Routing instance table that stores VRF routing information. See also VRF instance.

VRRP

Virtual Router Redundancy Protocol. On Fast Ethernet and Gigabit Ethernet interfaces, allows you to configure virtual default routers.

VSR

Video services router. A router used in a video services network to rout video streams between an access network and a metro or core network. The VSR is any M-series or MX-series router that supports the video routing package provided with JUNOS software Release 8.3 or later.

VT

Virtual loopback tunnel interface. VT interface that loops packets back to the Packet Forwarding Engine for further processing, such as looking up a route in a VRF routing table or looking up an Ethernet MAC address. A virtual loopback tunnel interface can be associated with a variety of MPLS and VPN-related applications, including VRF routing instances, VPLS routing instances, and point-to-multipoint LSPs.

W

WAN PHY

Wide Area Network Physical Layer Device. A physical layer device that allows 10-Gigabit Ethernet wide area links to use fiber-optic cables and other devices intended for SONET/SDH. See also LAN PHY and PHY.

WAP

Wireless Application Protocol. A standard protocol that enables mobile users to access the Internet in a limited fashion if WAP is supported and enabled on the mobile device, server, and wireless network. WAP users can send and receive e-mail and access Web sites in text format only (WAP does not support graphics).

warm standby

Method that enables one backup Adaptive Services (AS) PIC to support multiple active AS PICs, without providing guaranteed recovery times.

wavelength-division multiplexing

See WDM.

WCDMA

Wideband Code Division Multiple Access. Radio interface technology used in most third-generation (3G) systems.

WDM

Wavelength-division multiplexing. Technique for transmitting a mix of voice, data, and video over various wavelengths (colors) of light.

weighted round-robin

See WRR.

Wideband Code Division Multiple Access

See WCDMA.

Windows Internet Name Service

See WINS.

WINS

Windows Internet Name Service. A Windows name resolution service for network basic input/output system (NetBIOS) names. WINS is used by hosts running NetBIOS over TCP/IP (NetBT) to register NetBIOS names and resolve NetBIOS names to Internet Protocol (IP) addresses.

WRR

Weighted round-robin. Scheme used to decide the queue from which the next packet should be transmitted.

X

XENPAK

Standard that defines a type of pluggable fiber-optic transceiver module that is compatible with the 10-Gigabit Ethernet (10 GbE) standard.

XENPAK module

10-Gigabit Ethernet fiber-optic transceiver. XENPAK modules are hot-insertable and hot-removable. See also MSA.

XENPAK Multisource Agreement

See MSA.

XENPAK-SR 10BASE-SR XENPAK

Media type that supports a link length of 26 meters on standard Fiber Distributed Data Interface (FDDI) grade multimode fiber (MMF). Up to 300-meter link lengths are possible with 2000 MHz/km MMF (OM3).

XENPAK-ZR 10GBASE-ZR XENPAK

Media type used for long-reach, single-mode (80–120 km) 10-Gigabit Ethernet metro applications.

XFP

10-Gigabit small form-factor pluggable transceiver. A transceiver that provides support for fiber-optic cables. XFPs are hot-insertable and hot-removable. See also SFP.

XML

Extensible Markup Language. Language used for defining a set of markers, called tags, that define the function and hierarchical relationships of the parts of a document or data set.

XML Path Language

See XPath.

XML schema

Definition of the elements and structure of one or more Extensible Markup Language (XML) documents. Similar to a document type definition (DTD), but with additional information and written in XML.

XOR

Exclusive or. A logical operator (exclusive disjunction) in which the operation yields the result of true when one, and only one, of its operands is true.

XPath

Standard used in XSLT to specify and locate elements in the input document’s XML hierarchy. XPath is fully described in the W3C specification at http://w3c.org/TR/xpath.

XSLT

Extensible Stylesheet Language for Transformations. A standard for processing XML data developed by the World Wide Web Consortium (W3C). XSLT performs XML-to-XML transformations, turning an input XML hierarchy into an output XML hierarchy. The XSLT specification is on the W3C Web site at http://www.w3c.org/TR/xslt.

Z

zeroize

Process of removing all sensitive information, such as cryptographic keys and user passwords, from a router running JUNOS-FIPS.