In today's lecture, Dr. Gunes talked about how routing in the internet works. In the entirety of the internet, it would be impractical to store all the destinations in to a routing table. The tables would be very large and inefficient. Network administrators do not want to be told how to configure their own routers, so each network may be a little different from other networks. They are all autonomous systems (AS). Each network much communicate with itself with the same intra-autonomous system routing protocol, but for other ASes to communicate with each other, there must be a Gateway router to bind them directly together.
The forwarding tables in each AS must have a intra-routing table as well as an inter-routing table to communicate with external destinations. An example from the lecture shows the tasks of the Inter-AS. When a datagram from the inside needs to be delivered to the outside, the AS must learn how the destination can be communicated to and where it can be reached through. Once it is known, the AS propagates the information to all of the routers in its network, so they are informed of how to reach that destination.
In Intra-AS routing, there are a few common routing protocols. The ones mentioned in the lecture were Routing Information Protocol (RIP) and Open Shortest Path First (OSPF). RIP uses the distance vector algorithm mentioned in the last lecture and OSPF uses the link state algorithm mentioned previously as well. A major point of RIP is that constantly exchanges its distance vectors, also called advertisements, with its neighbors every thirty-seconds and the OSPF keeps a topological map at each of its nodes where its advertisements are flooded across the network.
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