Configuring Is-Is; Overview; Terminology; Address Format - HPE 5800 Series Configuration Manual

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.

Address format

NSAP
As shown in
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).
The DSP includes the High Order Part of DSP (HO-DSP), System ID, and SEL, where the HO-DSP
identifies the area, the System ID identifies the host, and the SEL identifies the type of service.
The IDP and DSP are variable in length. The length of an NSAP address varies from 8 bytes to 20
bytes.
Figure 35, an NSAP address comprises the Initial Domain Part (IDP) and the Domain
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