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 in the range 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 purposes.

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 forwarding the data packet to the next-hop router.

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.

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, and 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.

LFI

Link fragmentation and interleaving. For MLFR with PPP traffic or MLPPP with PPP traffic, 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.

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 a 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 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

Packets that contain information about the state of adjacencies to neighboring systems.

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 doesn't 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.

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

A 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:

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.

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 varies according to the version of the Internet Protocol ASIC in the router. Also called per-packet load balancing.

loading

OSPF adjacency state where 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 preference

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

local significance

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

local RIB

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

logical link control

See LLC.

logical operator

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

logical router

Logical routing device that is partitioned from an M-series or T-series routing platform. Each logical router 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.

loose

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

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-based 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.

LSP

  1. 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.)

  2.  
  3. See link-state PDU.

  4.  

LSQ

Link services intelligent queuing interfaces. Interfaces configured on the AS 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 can process label-switched packets.