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6.2 | |
Dynamic Routing Overview | |
| 6.2.3 | |
Purpose of a routing protocol and autonomous systems |
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The goal of a routing protocol is to build
and maintain the routing table. This table contains the learned
networks and associated ports for those networks. Routers use routing
protocols to manage information received from other routers,
information learned from the configuration of its own interfaces,
along with manually configured routes. The routing protocol learns all available routes, places the best routes into the routing table, and removes routes when they are no longer valid. The router uses the information in the routing table to forward routed protocol packets. The routing algorithm is fundamental to dynamic routing. Whenever the topology of a network changes because of growth, reconfiguration, or failure, the network knowledgebase must also change. The network knowledgebase needs to reflect an accurate consistent view of the new topology. When all routers in an internetwork are operating with the same knowledge, the internetwork is said to have converged. Fast convergence is desirable because it reduces the period of time in which routers would continue to make incorrect routing decisions. Autonomous systems (AS) provide the division of the global internetwork into smaller and more manageable networks. Each AS has its own set of rules and policies and an AS number that will uniquely distinguish it from other autonomous systems throughout the world.
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