Find MAC (and IP)

[Loftyworm]

I know you have all seen this before, but please hear me out.

I have a 4510 switch, loaded out.  I know for fact that I have MAC a.a.a.a coming out of port 2/10.  But I can't get my commands to show me this.

sh ip arp does return a whole list of IP's, but none of them are in the vlan I am expecting, and there are several vlans missing.  

I understand getting the IP is kinda tricky, and you have to run the MAC backword through the acting router, but it should at least tell me the MAC's it sees on a port, shouldn't it????  My only suspicion is that this is a voip port, and there are multiple MACs coming through a single port.  In my case with VM's, there may be 5 or more.

[Seb Rupik]

Hi there,

Do you have any VRFs configured on your switch?

sh ip vrf

The command sh ip arp will only show the arp cache for the default VRF. There is a good chance this vlan belongs to a different VRF.

Under the L3 interface configuration for the subnet in question there should be a line:

vrf forwarding xxxx

..include the 'xxxx' into the follow command:

sh ip arp vrf xxxx

or more specifically:

sh ip arp vrf xxxx vlan xx

Alternatively just use the command sh mac address-table which is a L2 command so is VRF agnostic.

cheers,

Seb.

[Loftyworm · Accepted solution]

I see this is still up.  I will say I found that this 4510 witch was acting like a router on a stick and that the show mac address-table was able to give me the port after I got the MAC from the Router.