Is-Is Overview; Is-Is Terminology - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

IS-IS Overview

IS-IS Terminology

536
ICMP Router Discovery Overview
MPLS Overview for ACX Series Universal Access Routers on page 587
Configuring Junos OS for IPv6 Path MTU Discovery
IPv6 Neighbor Discovery Overview
The IS-IS protocol is an interior gateway protocol (IGP) that uses link-state information
to make routing decisions.
IS-IS is a link-state IGP that uses the shortest-path-first (SPF) algorithm to determine
routes. IS-IS evaluates the topology changes and determines whether to perform a full
SPF recalculation or a partial route calculation (PRC). This protocol originally was
developed for routing International Organization for Standardization (ISO) Connectionless
Network Protocol (CLNP) packets.
Like OSPF routing, IS-IS uses hello packets that allow network convergence to occur
quickly when network changes are detected. IS-IS uses the SPF algorithm to determine
routes. Using SPF, IS-IS evaluates network topology changes and determines if a full or
partial route calculation is required.
NOTE: Because IS-IS uses ISO addresses, the configuration of IP version 6
(IPv6) and IP version 4 (IPv4) implementations of IS-IS is identical.
NOTE: See Platforms/FPCs That Cannot Forward TCC Encapsulated ISO
Traffic to find a list of those devices and FPC configurations that cannot pass
ISO traffic when encapsulated in TCC format.
This section discusses the following topics:
IS-IS Terminology on page 536
ISO Network Addresses on page 537
IS-IS Packets on page 539
Persistent Route Reachability on page 540
IS-IS Support for Multipoint Network Clouds on page 540
Installing a Default Route to the Nearest Routing Device That Operates at Both IS-IS
Levels on page 540
An IS-IS network is a single autonomous system (AS), also called a routing domain, that
consists of end systems and intermediate systems. End systems are network entities that
send and receive packets. Intermediate systems send and receive packets and relay
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