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How does Router Y know about Network A? How does Router X know about Network C?

How does Router Y know about Network A? How does Router X know about Network C?. One Solution. Static Routes Effective in simple networks without alternate paths Still difficult to configure if you have, for example, 20 routers and 100 networks in a tree structure. ROUTER X:

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How does Router Y know about Network A? How does Router X know about Network C?

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  1. How does Router Y know about Network A? How does Router X know about Network C?

  2. One Solution • Static Routes • Effective in simple networks without alternate paths • Still difficult to configure if you have, for example, 20 routers and 100 networks in a tree structure.

  3. ROUTER X: ip route 192.168.3.0 255.255.255.0 192.168.2.2 ROUTER Y: ip route 192.168.1.0 255.255.255.0 192.168.2.1

  4. What is the best path from Net 1 to Net 3? If a Link goes down, can an alternate path be determined correctly and quickly?

  5. Routing Protocols • Communication between routers to share information about the reachability and status of networks. • The ultimate goal is to allow hosts to communicate with other hosts. • Most hosts will not participate in these routing protocols. The internetwork is an abstract service, much like a file system.

  6. Routing Protocol Basics A routing algorithm must: • Pass reachability info to other routers • Receive reachability info from other routers • Determine optimal routes • React to changes

  7. RIP • Routing Information Protocol • Popularity due to distribution of Berkeley UNIX (1982) and routing daemon: routed • Distance Vector ( Bellman-Ford) routing protocol • RIP v1 is classful, RIP v2 is classless.

  8. RIP Algorithm Basics • Advertise my directly connected networks, with a metric (hop count) of 1, via broadcast on my directly connected networks,. • Listen. If I hear other RIP advertisements, add to my route table if the network is new to me, or if the metric is better. • Re-advertise periodically, including nets that I heard about. (Add 1 to these metrics).

  9. More RIP details • Split Horizon - Don’t announce routes I learned back out the same interface. • Poison Reverse – Announce routes back out the same interface, but with metric 16 (unreachable). • Ethereal sniffer

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