Network Glossary J K L

Join/Prune message Sent by a PIM router to its upstream router to either request that the upstream router forward the group traffic or stop forwarding the group traffic that is currently being forwarded. If a PIM router wants to start receiving the group traffic, it lists the group address under the Join field. If it wants the upstream router to stop forwarding the group traffic, it lists the group address under the Prune field.

joining a group The process of installing a multicast application; also referred to as launching an application.

K value EIGRP (and IGRP) allows for the use of bandwidth, load, delay, MTU, and link reliability; the K values refer to an integer constant that includes these five possible metric components. Only bandwidth and delay are used by default, to minimize recomputation of metrics for small changes in minor metric components.

label binding In MPLS, the mapping of an IP prefix and a label, which is then advertised to neighbors using LDP.

Label Distribution Protocol The RFC-standard MPLS protocol used to advertise the binding (mapping) information about each particular IP prefix and associated label. See also TDP.

Label Forwarding Information Base An MPLS data structure used for forwarding labeled packets. The LFIB lists the incoming label, which is compared to the incoming packet’s label, along with forwarding instructions for the packet.

Label Switch Router An MPLS term referring to any device that can forward packets that have MPLS labels.

label switched path The combination of MPLS labels and links over which a packet will be forwarded over an MPLS network, from the point of ingress to the MPLS network to the point of egress.

LACP See Link Aggregation Control Protocol.

LAPF See Link Access Procedure for Frame-Mode Bearer Services.

Layer 2 payload compression The process of taking the payload inside a Layer 2 frame, including the headers of Layer 3 and above, compressing the data, and then uncompressing the data on the receiving router.

Layer 2 protocol tunneling Another name for 802.1Q-in-Q. See 802.1Q-in-Q.

Layer x PDU The PDU used by a particular layer of a networking model, with x defining the layer.

LCP See Link Control Protocol.

LDP See Label Distribution Protocol.

Lead Content Engine The content engine in a WCCP cluster, which determines how traffic will be distributed within the cluster.

learning state An 802.1d STP transitory port state in which the port does not send or receive frames, but does learn the source MAC addresses from incoming frames.

LFI See Link Fragmentation and Interleaving.

LFIB See Label Forwarding Information Base.

limiting query scope (EIGRP) An effort to reduce the query scope with EIGRP, using route summarization or EIGRP stub routers.

line coding See encoding.

Link Access Procedure for Frame-Mode Bearer Services An ITU standard Frame Relay header, including the DLCI, DE, FECN, and BECN bits in the LAPF header, and a frame check in the LAPF trailer.

Link Aggregation Control Protocol Defined in IEEE 802.1AD, defines a messaging protocol used to negotiate the dynamic creation of PortChannels (EtherChannels) and to choose which ports can be placed into an EtherChannel.

Link Control Protocol The portion of PPP focused on features that are unrelated to any specific Layer 3 protocol.

Link Fragmentation and Interleaving The process of breaking a frame into pieces, sending some of the fragments, and then sending all or part of a different packet, all of which is done to reduce the delay of the second packet.

link-local An address type in IPv6 networks that is used only on the local link and never beyond that scope.

Link-State Acknowledgment A type of OSPF packet used to acknowledge LSU packets.

link-state advertisement The OSPF data structure that describes topology information.

link-state database The data structure used by OSPF to hold LSAs.

link-state routing protocol Any routing protocol that uses the concept of using the SPF algorithm with an LSDB to compute routes.

Link-State Update A type of OSPF packet, used to communicate LSAs to another router.

listening state An 802.1d STP transitory port state in which the port does not send or receive frames, and does not learn MAC addresses, but does wait for STP convergence and for CAM flushing by the switches in the network.

LLQ See low-latency queuing.

LMI See Local Management Interface.

local computation An EIGRP router’s reaction to an input event, leading to the use of a feasible successor or going active on a route.

local label In MPLS, a term used to define a label that an LSR allocates and then advertises to neighboring routers. The label is considered “local” on the router that allocates and advertises the label.

LOCAL_AS A reserved value for the BGP COMMUNITY path attribute that implies that the route should not be advertised outside the local confederation sub-AS.

Local Management Interface The Frame Relay protocol used between a DCE and DTE to manage the connection. Signaling messages for SVCs, PVC Status messages, and keepalives are all LMI messages.

LOCAL_PREF A BGP path attribute that is communicated throughout a single AS to signify which route of multiple possible routes is the best route to be taken when leaving that AS. A larger value is considered to be better.

LOF See Loss of Frame.

Loop Guard Protects against problems caused by unidirectional links between two switches. Watches for loss of received Hello BPDUs, in which case it transitions to a loop-inconsistent state instead of transitioning to a forwarding state.

loopback circuitry A feature of Ethernet NICs. When the NIC transmits an electrical signal, it “loops” the transmitted electrical current back onto the receive pair. By doing so, if another NIC transmits a frame at the same time, the NIC can detect the overlapping received electrical signals, and sense that a collision has occurred.

LOS Loss of Signal. A T1 alarm state that occurs when the receiver has not received any pulses of either polarity for a defined time period.

Loss of Frame A T1 alarm state that occurs when the receiver can no longer consistently identify the frame.

low-latency queuing A Cisco IOS queuing tool that uses MQC configuration commands, reserves a minimum bandwidth for some queues, provides high-priority scheduling for some queues, and polices those queues to prevent starvation of lower-priority queues during interface congestion.

LSA See link-state advertisement.

LSA flooding The process of successive neighboring routers exchanging LSAs such that all routers have an identical LSDB for each area to which they are attached.

LSA type (OSPF) A definition that determines the data structure and information implied by a particular LSA.

LSAck See Link-State Acknowledgment.

LSDB See link-state database.

LSP See label switched path.

LSP segment A single label and link that is part of a complete LDP. See also label switched path.

LSR See Label Switch Router.

LSRefresh Link-State Refresh. A timer that determines how often the originating router should reflood an LSA, even if no changes have occurred to the LSA.

LSU See Link-State Update.

LxPDU See Layer x PDU.

LZS The Lempel Ziv STAC compression algorithm is used in Frame Relay networks to define dynamic dictionary entries that list a binary string from the compressed data and an associated smaller string that represents it during transmission—thereby reducing the number of bits used to send data.