Collection of files that make up a JUNOS software component.


Data packets and local packets. Data packets are chunks of data transiting the router as they are forwarded from the source to a destination. Local packets are chunks of data that are destined for or sent by the Routing Engine.

packet data protocol

See PDP.

Packet Forwarding Engine

Architectural 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.


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.


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.


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.


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.


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


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.

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).


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


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


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


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

peak information rate

See PIR.


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


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


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


  1. Privacy Enhanced Mail. A technique for securely exchanging electronic mail over a public medium.

  3. Power Entry Module. Distributes DC power within the router chassis. Supported on M40e, M160, M320, and T-series routers.


penultimate hop popping

See PHP.

penultimate router

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

Perfect Forward Secrecy

See PFS.

Peripheral Component Interconnect

See PCI.

permanent virtual circuit

See PVC.

persistent change

A 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


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).


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 in the range 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.


Perfect Forward Secrecy protocol. A condition derived from an encryption system that changes encryption keys often and ensures that no two sets of keys have any relation to each other. The advantage of PFS is that 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.


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.


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


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

Physical Interface Card

See 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.


Protocol Independent Multicast. A protocol-independent multicast routing protocol. PIM sparse mode routes to multicast groups that might span wide-area and interdomain internets. PIM dense mode is a flood-and-prune protocol.


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 and PIR.


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


Packet loss priority. Used to determine the random early detection (RED) drop profile when queuing a packet. 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.


Point of local repair. The head-end of a backup tunnel or a detour LSP.

point of local repair

See PLR.

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

An 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.

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.


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.

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.


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


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.


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


PPPoE Active Discovery Offer packet


PPPoE Active Discovery Request packet


PPPoE Active Discovery Session-Confirmation packet


PPPoE Active Discovery Termination packet


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.


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 in the range 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.


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.

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 PIM.

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 edge router

See PE router.

provider router

Router in the service provider's network that does not attach 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.


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.


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

Public Land Mobile Network



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


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