autonomous system --A collection of networks that share the same routing protocol and that are under the same system administration.
ASBR --autonomous system boundary router. A router that connects and exchanges information between two or more autonomous systems.
backup tunnel --A Multiprotocol Label Switching (MPLS) traffic engineering tunnel used to protect other (primary) tunnel traffic when a link or node failure occurs.
DSCP --differentiated services code point. Six bits in the IP header, as defined by the Internet Engineering Task Force (IETF). These bits determine the class of service provided to the IP packet.
FRR --Fast Reroute. A mechanism for protecting Multiprotocol Label Switching (MPLS) traffic engineering (TE) label switched paths (LSPs) from link and node failure by locally repairing the LSPs at the point of failure, allowing data to continue to flow on them while their headend routers attempt to establish end-to-end LSPs to replace them. FRR locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or nodes.
graceful restart --A process for helping a neighboring Route Processor (RP) restart after a node failure has occurred.
headend --The router that originates and maintains a given label switched paths (LSP). This is the first router in the LSP’s path.
IGP --Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include Internal Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).
IS-IS --Intermediate System-to-Intermediate System. Open systems Interconnection (OSI) link-state hierarchical routing protocol whereby Intermediate System (IS) routers exchange routing information based on a single metric to determine network topology.
instance --A mechanism that implements the RSVP hello extensions for a given router interface address and remote IP address. Active hello instances periodically send Hello Request messages, expecting Hello ACK messages in response. If the expected ACK message is not received, the active hello instance declares that the neighbor (remote IP address) is unreachable (that is, it is lost). This can cause LSPs crossing this neighbor to be fast rerouted.
label --A short, fixed-length data identifier that tells switching nodes how to forward data (packets or cells).
LDP --Label Distribution Protocol. The protocol that supports Multiprotocol Label Switching (MPLS) hop-by-hop forwarding by distributing bindings between labels and network prefixes. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).
LSP --label switched path is a configured connection between two routers, in which Multiprotocol Label Switching (MPLS) is used to carry packets. The LSP is created by the concatenation of one or more label-switched hops, allowing a packet to be forwarded by swapping labels from one MPLS node to another MPLS node.
merge point --The backup tunnel’s tail.
MPLS --Multiprotocol Label Switching. A method for forwarding packets (frames) through a network. MPLS enables routers at the edge of a network to apply labels to packets (frames). ATM switches or existing routers in the network core can switch packets according to the labels.
OSPF --Open Shortest Path First. A link-state routing protocol used for routing.
PLR --point of local repair. The headend of the backup tunnel.
RSVP --Resource Reservation Protocol. A protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of the packet streams they want to receive.
state --Information that a router must maintain about each LSP. The information is used for rerouting tunnels.
tailend --The router upon which an LSP is terminated. This is the last router in the LSP’s path.
TE --traffic engineering. The techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods had been used.
topology --The physical arrangement of network nodes and media within an enterprise networking structure.
tunnel --Secure communications path between two peers, such as two routers.
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental. © 2004-2011 Cisco Systems, Inc. All rights reserved.