H3C Technologies H3C SR8800 - Manual (Page 152)

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Configuring IS-IS
IS-IS 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).
The IS-IS routing protocol was modified and extended in RFC 1195 by the International Engineer Task
Force (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 Interior Gateway Protocol (IGP) used within an Autonomous System. It adopts the Shortest Path
First (SPF) algorithm for route calculation.
Basic concepts
IS-IS terminology
• Intermediate system (IS)—Similar to a router in TCP/IP, it 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)—Refers to a host system in TCP/IP. ISO defines the ES-IS protocol for
communication between an ES and an IS. An ES does not participate in the IS-IS processing.
• Routing domain (RD)—A group of ISs exchanges routing information with each other using the
same routing protocol in a routing domain.
• Area—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. Each IS has at least one
LSDB. 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)—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 49 , an NSAP address consists of 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).