H3C Technologies H3C S12500 Series Switches - Manual (Page 148)

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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 adopts the SPF algorithm for route calculation.
Terminology
• Intermediate system (IS)—An IS, similar to a router in TCP/IP, is the basic unit in IS-IS to generate
and propagate routing information. In the following text, an IS refers to a router.
• End system (ES)—An ES refers to a host system in TCP/IP. ISO defines the ES-IS protocol for
communication between an ES and an IS; therefore, an ES does not participate in the IS-IS
processing.
• Routing domain (RD)—An RD is a group of ISs exchanges routing information with each other using
the same routing protocol in a routing domain.
• Area—An area is a unit in a routing domain. The IS-IS protocol allows a routing domain to be
divided into multiple areas.
• Link State Database (LSDB)—All link states in the network forms the LSDB. There is at least one LSDB
in each IS. The IS uses the SPF algorithm and LSDB to generate its own routes.
• Link State Protocol Data Unit (LSPDU) or Link State Packet (LSP)—Each IS can generate an LSP,
which contains all the link state information of the IS.
• Network Protocol Data Unit (NPDU)—An NPDU is a network layer protocol packet in OSI, which is
equivalent to an IP packet in TCP/IP.
• Designated IS—On a broadcast network, the designated router is also known as the designated IS.
• 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 in the OSI reference
model.
IS-IS address format
NSAP
As shown in Figure 52 , 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.