Internet Protocol (IP) routing protocols are used to dynamically determine the best routes to send data from a source to a destination via routers or networks, while taking the network situation into account. A routing protocol shares the information with neighbor routers and throughout the network. IP routing protocols enable routers to dynamically build up and update their routing tables. The routing table contains destination information along with the corresponding output ports (i.e., the next hops) to which packets should be sent. Thus, packets are transmitted in a hop-by-hop manner, guided by the routing tables of each router on the route from the source to the destination.

The concept of the routing table is similar to a guide post on the road. In Figure 4.1a, a car driver wants to go to the airport. At the junction, the driver turns to the left based on the road sign. In Figure 4.1b, a packet arrives at the router. Its destination is The router forwards the packet to output port 2 based on the information in the routing table.

This chapter describes IP routing protocols. Section 4.1 describes an overview of routing protocols including Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP), as shown in Figure 4.2. Section 4.2 describes the Routing Information Protocol (RIP) as an IGP. Section 4.3 describes the Open Shortest Path First (OSPF) protocol as another example an an IGP. Section 4.4 describes the Border Gateway ...

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