When the frame arrived at the port router, the router frame examination of the address field goal, if the destination address for the router interface, or address broadcast address, the router packet from the spin-off in the frame, transmission To the network layer, and then in the packet destination address will be checked, also check the next protocol field, and then sent to the appropriate process, if the packet is routed, the router will find their own routing table to find The corresponding routing entries, routing entries at least two elements:

1, destination address, the address of the router must be able to arrive at the address;

2, arrived at the destination address pointer, this guide is what we usually see in the routing table of Via. Peacetime or heard of the next-hop

According to the router packet in the address field goal in the implementation of the routing table inquiries, inquiries by the accuracy of the following descending order:

1, host address

2, subnet address

3, the network summary,

4, the main type of network,

5, super net

6, the default routing

If the implementation of all forms of inquiry, not to find the matching entries, then discarded packet, and sent back to a (Destinnation Unreachable) ICMP unreachable message to the sender

CISCO routers in the routing table to see, you can use the privilege command: show ip route,following is picture of ip route.

ip router table

If you just want to check the static routing entries, you can show ip route in order to add static parameters, and so on … …