для Cisco Cisco IOS Software Release 12.0(29)S

AS—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—An MPLS Traffic Engineering tunnel used to protect other (primary) tunnels’ traffic 
when a link or node failure occurs.

DSCP—Differentiated Services Code Point. Six bits in the IP header, as defined by the IETF. These bits 
determine the class of service provided to the IP packet.

Fast Reroute—A mechanism for protecting MPLS Traffic Engineering (TE) 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 restart after a node failure has 
occurred.

headend—The router that originates and maintains a given 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 IGRP, OSPF, and RIP. 

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 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. A configured connection between two routers, in which MPLS is used to 
carry packets. A path created by the concatenation of one or more label switched hops, allowing a packet 
to be forwarded by swapping labels from an MPLS node to another MPLS node. 

merge point—The tail of the backup tunnel. 

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. 

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.