9-10 CHAPTER 9: ADMINISTERING IP ROUTING

more than one routing table entry matching an address, it uses the most specific route, which is the route with the most bits set in its subnet mask. For example, the route to a subnet within a destination network is more specific than the route to the destination network.

Routing Metric — This metric specifies the number of networks or subnets through which a packet must pass to reach its destination. This metric is included in RIP updates to allow routers to compare routing information received from different sources.

Gateway IP Address — This address tells the router how to forward packets whose destination addresses match the route’s IP address and subnet mask. The system forwards such packets to the indicated gateway.

Status — For each interface, the route provides the status information in Table 9-1.

Table 9-1 Interface Status Information

Status

Description

 

 

Direct

Route goes to a directly connected network

Static

Route was statically configured

Learned

Route was learned using indicated protocol

Timing out

Route was learned but is partially timed out

Timed out

Route has timed out and is no longer valid

 

 

In addition to the routes to specific destinations, the routing table can contain an additional entry called the default route. The system uses the default route to forward packets that do not match any other routing table entry. You might want to use a default route in place of routes to numerous destinations that all have the same gateway IP address.

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3Com 2500 Interface Status Information Description Direct, Static Route was statically configured Learned, Timing out