Hard to find port for given MAC

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Sep 23rd, 2010
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I have a 6509 (R7000), I want to locate the port traffic is going through for a server. I have the server's ip; so I ping the server(using the respective vrf), then sh ip arp vrf <VRF> <target ip>, then sh mac-address-table address <MAC found on previous command> but got no results.

There are two servers using different IPs, but the same MAC, one does respond to ping and the other doesn't, however, when I run the sh ip arp for both of them, the same MAC comes up; still, there is no port for the sh mac-address-table command.

What is missing?

I need to find where these servers are physically attached to.

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NickNac79 Thu, 09/23/2010 - 02:45
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Hi Mariano,

This is probably a stupid question, but are you certain that the MAC address you found is the interface of the server, and not a gateway address?

You can try specifying the vlan when you run the show mac address-table command - this can sometimes help.

Are you running CDP in your network & do you have access to the server?  If so you can use Wireshark to capture the CDP packets and see the device & port it is attached to.

Hope this helps :-)


mariorod1 Thu, 09/23/2010 - 03:01
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Thanks Nick!

I specified the vlan before without results, but jus a moment ago, I'm getting two different MACs for each, and specific ports. Although the MAC addresses I found now are different from the database. It's likely they are doing something with the servers, but I had no results when the mac was "correct" though.


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