57 IS-IS CONFIGURATIONWhen configuring IS-IS, go to these sections for information you are interested in:■ “IS-IS Overview” on page 877■ “IS-IS Configuration Task List” on page 892■ “Configuring IS-IS Basic Functions” on page 893■ “Configuring IS-IS Routing Information Control” on page 894■ “Tuning and Optimizing IS-IS Network” on page 898■ “Configuring IS-IS GR” on page 904■ “Displaying and Maintaining IS-IS Configuration” on page 905■ “IS-IS Configuration Example” on page 906IS-IS Overview Intermediate System-to-Intermediate System (IS-IS) is a dynamic routing protocoldesigned by the International Organization for Standardization (ISO) to operate onthe connectionless network protocol (CLNP).The IS-IS routing protocol has been modified and extended in RFC 1195 by theInternational Engineer Task Force (IETF) for application in both TCP/IP and OSIreference 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. Itadopts the Shortest Path First (SPF) algorithm for route calculation.Basic Concepts IS-IS terminology■ Intermediate system (IS). An IS, similar to a router in TCP/IP, is the basic unit inIS-IS protocol to generate and propagate routing information. In the followingtext, an IS is a router.■ End system (ES). An ES refers to a host system in TCP/IP. ISO defines the ES-ISprotocol for communication between an ES and an IS, therefore an ES does notparticipate in the IS-IS process.■ Routing domain (RD). A group of ISs exchange routing information with thesame routing protocol in a routing domain.■ Area. An area is a division unit in a routing domain. The IS-IS protocol allows arouting domain to be divided into multiple areas.■ Link State Database (LSDB). All link states in the network forms the LSDB. Thereis at least one LSDB in each IS. The IS uses SPF algorithm and LSDB to generateits own routes.
