IP Routing is a process that forward packets from one network to another network. A device called router is used to perform the IP routing functions. Whenever a router receives a packet, it checks the source and destination addresses mentioned in the packet. The router matches the packet with its routing database and decides whether the packet needs to be forwarded or dropped. If the destination address matches in the routing database, the router forwards it to gateway address for the appropriate network. If the destination network address does match in the routing table, the router discards the packet and sends the Destination host unreachable message to the source device. However, one can set a gateway of last resort to forward packets for the destinations that are not listed in the routing table. This is done by setting the default route.
What is Routing Table?
A Routing table contains information needed for a router to forward packets to a next hop relay device. It contains the destination network, destination prefix, and the gateway address for the remote networks. The following figure shows a sample of a routing table.
In the preceding figure, the first highlighted box contains the various codes used to describe the routing methods. The second highlighted box displays a sample of a route entry. [Read more…]