R3303-HP HSR6800 Routers Layer 3 - IP Routing Configuration Guide

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Configuring IS-IS
This chapter describes how to configure IS-IS for an IPv4 network.
Overview
Intermediate System-to-Intermediate System (IS-IS) is a dynamic routing protocol designed by the
International Organization for Standardization (ISO) to operate on the connectionless network protocol
(CLNP).
IS-IS was modified and extended in RFC 1195 by the IETF for application in both TCP/IP and OSI
reference models, and the new one is called "Integrated IS-IS" or "Dual IS-IS."
IS-IS is an IGP used within an AS, and uses the SPF algorithm for route calculation.
Terminology
• Intermediate system (IS)—Similar to a router in TCP/IP, it is the basic unit in an IS-IS routing domain
to generate and propagate routing information. In the following text, an IS refers to a router.
• End system (ES)—Similar to a host system in TCP/IP, an ES does not run IS-IS. ISO defines the ES-IS
protocol for communication between an ES and an IS.
• Routing domain (RD)—An RD comprises a group of ISs that exchange routing information with each
other by using the same routing protocol.
• Area—An IS-IS routing domain can be split into multiple areas.
• Link State Database (LSDB)—All link states in the network forms the LSDB. Each IS has at least one
LSDB. An IS uses the SPF algorithm and LSDB to generate IS-IS routes.
• Link State Protocol Data Unit (LSPDU) or Link State Packet (LSP)—An IS advertises all its link state
information in an LSP.
• Network Protocol Data Unit (NPDU)—A network layer protocol packet in OSI, similar to an IP
packet in TCP/IP.
• Designated IS—Elected on a broadcast network.
• Network service access point (NSAP)—An NSAP is an OSI network layer address. It identifies an
abstract network service access point and describes the network address format in the OSI
reference model.
IS-IS address format
NSAP
As shown in Figure 34, an NSAP address comprises the initial domain part (IDP) and the domain specific
part (DSP). The IDP is equal to the network ID of an IP address, and the DSP is equal to the subnet and
host ID.
The IDP includes the authority and format identifier (AFI) and the initial domain identifier (IDI).