Please define

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Feb 19th, 2008
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Please define the following commands for me and why they are used. I cannot find definitions for them anywhere, and I don't want to wait another week to ask my instructor:

* ip classless

* ip subnet-zero

* no ip domain-lookup

All of these commands are entered at the config prompt.

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lamav Tue, 02/19/2008 - 17:41
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ip subnet zero enables the use of subnet zero for interface addresses and routing updates. Subnetting with a subnet address of zero is illegal and strongly discouraged (as stated in RFC 791) because of the confusion that can arise between a network and a subnet that have the same addresses. For example, if network is subnetted as, subnet zero would be written as is identical to the network address.

no ip domain lookup disables DNS lookups (hostname to ip address mapping) for host names. For example, if you enter "ping" at the hostname prompt, the PING test will not be executed successfully because the router cannot do the ip address mapping for the FQDN. The same is true if a network administrator wants to telnet from one router to another by using the router's hostname, ie "telnet hostname2."

ip classless enables classless routing behavior, ie. CIDR, VLSM.

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