IP Routes and Routing Tables

As described in the previous section, routers are responsible for forwarding traffic on an IP internetwork. Each router accepts datagrams from a variety of sources, examines the IP address of the destination, and decides the next hop that the datagram needs to take to get it that much closer to its final destination. But how does a router know where to send different datagrams?

Each router maintains a set of information that provides a mapping between different network IDs and the other routers to which it is connected. This information is contained in a data structure normally called a routing table. Each entry in the table, called a routing entry, provides information about one network (or subnetwork or host). It ...

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