Intermediate System Routing Protocol IS-IS is a routing protocol proposed by ISO. It is a link status protocol, in which IS (router) is responsible for exchange routing information and determines the network topology. Like the open shortur path to the TCP / IP network priority OSPF protocol.
The ISO network contains terminal systems, intermediate systems, regions, and domains. The terminal system refers to a user equipment, an intermediate system refers to a router. The local group of the router is called "region", and multiple regions form a "domain". IS-IS is designed to provide routing services in the domain or in a region. ES-IS combines with CLNP, IS-IS, and IDRP, providing a full routing process for the entire network.
The IS-IS routing system is divided into two layers. The Level 1 router only knows the topology in this area, including all routers and hosts, instead of the router identity and destination other than the area. Level 1 In the region you know Level 2, all traffic will be sent to the nearest L2 router. The Level 2 router does not need to know the topology in any Level 1 area, unless the Level 2 router is a certain level of Level 1 in a single area, unless the Level 2 router is a single area.
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