Operation Manual – Routing ProtocolH3C S7500 Series Ethernet Switches Chapter 5 IS-IS Configuration5-2of the IS. Each IS collects all the LSPs in the local area to generate its ownLSDB.z Network protocol data unit (NPDU). An NPDU is a network layer protocol packetin OSI, which is equivalent to an IP packet in TCP/IP.z Designated IS (DIS). On a broadcast network, the designated router is alsoknown as the designated IS.z Network service access point (NSAP). The NSAP is the OSI network layeraddress. It identifies an abstract network service access point and describes thenetwork address in the OSI reference model.II. IS-IS network typesIS-IS supports two network types:z Broadcast networks, such as Ethernet and Token-Ringz Point-to-point networks, such as PPP and HDLCFor non-broadcast multi-access (NBMA) network, such as ATM, you need toconfigure point-to-point or broadcast network on its sub-interfaces. IS-IS does not runon point to multipoint (P2MP) links.5.1.2 IS-IS DomainI. Two-level hierarchyThe IS-IS uses two-level hierarchy in the routing domain to support large scale routingnetworks. A large routing domain is divided into multiple Areas. The Level-1 router isin charge of forwarding routes within an area, and the Level-2 router is in charge offorwarding routes between areas.II. Level-1 and Level-21) Level-1 routerThe Level-1 router only forms the neighbor relationship with Level-1 and Level-1-2routers in the same area. The LSDB maintained by the Level-1 router contains thelocal area routing information. It directs the packets out of the area to the nearestLevel-2 router.2) Level-2 routerThe Level-2 router forms the neighbor relationship with the Level-2 and Level-1-2routers in the same or in different areas. It maintains a Level-2 LSDB which containsrouting information for routing between areas. All Level-2 routers must be contiguousto form the backbone in a routing domain. Only Level-2 routers can directlycommunicate with routers outside the routing domain. Level-2 routers in a routingdomain must be contiguous to ensure a contiguous backbone network.3) Level-1-2 router
