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Understanding the network.pdf - Back to Home

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not active, it is quite common for dial-on-demand and dial access-servers <strong>to</strong> use<br />

<strong>network</strong> address space on interfaces that are not available all <strong>the</strong> time. Static routes<br />

are usually used <strong>to</strong> provide reachability information in <strong>the</strong>se situations. An<br />

alternative is <strong>to</strong> use a loopback interface, which acts as a placeholder for <strong>the</strong><br />

<strong>network</strong>, and allows it <strong>to</strong> be announced dynamically.<br />

In addition <strong>to</strong> <strong>the</strong> basic form of <strong>the</strong> command, <strong>the</strong> form of <strong>the</strong> command can be quite useful.<br />

displays all <strong>the</strong> <strong>network</strong> routing information about all <strong>the</strong> active router interfaces:<br />

Router>sh ip route connected<br />

C 192.168.0.0/24 is directly connected, Serial0<br />

192.168.1.0/26 is subnetted, 3 subnets<br />

C 192.168.1.64 is directly connected, E<strong>the</strong>rnet0<br />

C 192.168.1.192 is directly connected, Loopback2<br />

C 192.168.1.128 is directly connected, Loopback1<br />

Router><br />

The command will display all <strong>the</strong> routing entry<br />

information for <strong>the</strong> specified <strong>network</strong> or host:<br />

Router>sh ip route 172.16.191.1<br />

Routing entry for 172.16.191.0/24<br />

Known via "static", distance 20, metric 0<br />

Routing Descrip<strong>to</strong>r Blocks:<br />

* 192.168.0.2<br />

Route metric is 0, traffic share count is 1<br />

Router><br />

This command variant is quite useful when debugging route announcement issues<br />

that arise when you use dynamic routing pro<strong>to</strong>cols and route redistribution.<br />

The command is also invaluable when you're<br />

employing classful or classless subnetting. Errors in subnetting large address<br />

spaces are common. This command lists all <strong>the</strong> mask variations used with a given IP<br />

address space:

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