L

label

In MPLS, a 20-bit unsigned integer in the range 0 through 1048575, used to identify a packet traveling along an LSP.

Label Distribution Protocol (LDP)

A signaling protocol used to establish an MPLS label- switched path. LDP uses the IGP shortest-path cost to each egress router in the network and is not capable of utilizing traffic-engineering concepts.

label object

An RSVP message object that contains the label value allocated by 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

An 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 (LSP)

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, simplex connection from the ingress router to the egress router. (The ingress and egress routers cannot be the same router.)

label switching

See Multiprotocol Label Switching (MPLS).

label-switching router (LSR)

A router on which MPLS is enabled and is thus capable of processing label-switched packets.

label values

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

Lightweight Directory Access Protocol (LDAP)

Software protocol used for locating resources on a public or private network.

line loopback

A method used to troubleshoot a problem with a physical transmission media. 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-state acknowledgment

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

link-state advertisement (LSA)

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

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 (LSP)

Packets that contain information about the state of adjacencies to neighboring systems in an IS-IS network.

link-state request list

A 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 onto this list.

link-state request packet

OSPF data packet that a router uses to request database information from a neighboring router.

link-state update

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

loading

OSPF adjacency state where the local router is sending link-state request packets to its neighbor and is awaiting the appropriate link-state updates from that neighbor.

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 operator

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

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

Router in an MPLS named-path that is not required to be directly connected to the local router.