Switch IP Question

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Jul 30th, 2007
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Is there an easy way to resolve a host mac address to an ip address within IOS for switches? - The only possible way I can see is to do a show mac-address-table to correlate a mac address to a switchport, and then run a show interfaces command and work through each interface on a switch one by one.

Is that the only possible way?



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Overall Rating: 5 (2 ratings)
Edison Ortiz Mon, 07/30/2007 - 12:36
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How about,

show arp | i [insert mac-address]

megg1ttdefence Mon, 07/30/2007 - 12:38
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Hi Edison,

Does that work for all Catalyst switches, or only multilayer switches?


etienne.basset Mon, 07/30/2007 - 23:41
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'sh arp' <> only if your switch has an IP address in the vlan. Otherwise you have to correlate your 'mac-address-table' with arp table on a server connected to your vlan



Edison Ortiz Tue, 07/31/2007 - 07:01
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As Etienne stated, the switch must have a L3 interface that belongs to the same subnet as the intended mac-address, therefore if you have multiple vlans, you need a multilayer switch and with a single vlan, any Catalyst swich with a L3 interface belonging on that single vlan.

Keep in mind, in order to have an ARP entry in the CAM, the switch or the device had to have some kind of L3 communication (for instance, ping). In a multilayer switch, you will find everyone's mac-address since this switch is usually everyone's default gateway.

If you have an external router as the default gateway for any segment, this device will contain the ARP table for that network/subnet.

megg1ttdefence Tue, 07/31/2007 - 07:19
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Etienne / Edison,

Thanks guys, think I understand now. Thanks for helping out.


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