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Switchport mapping

I had to map the ports on a 2960 switch. I had to fill in the missing name on each port with the PC that connect to it.

This is a simple task that only require one command on the switch:

SWITCH#show mac-address-table interface fastEthernet 0/20
Mac Address Table
Vlan    Mac Address       Type        Ports
—-    ———–       ——–    —–
201    000f.2034.4b2f DYNAMIC     Fa0/20
Total Mac Addresses for this criterion: 1

I now hold the MAC address of the PC that connect to port 20: 000f.2034.4b2f

The next step is finding the IP address that match this MAC address. To find this piece of information I used my L3 switch that connect the 2960 switch.
This is the arp command to run on the L3 switch:

L3SWITCH#show arp | include Vlan201
Internet        26   000b.cdf5.b4e4  ARPA   Vlan201
Internet         7   0018.4d76.a2be  ARPA   Vlan201
Internet         5   0018.fe6b.187f  ARPA   Vlan201
Internet         0   0026.553e.050a  ARPA   Vlan201
Internet        78   000f.fe2e.290e  ARPA   Vlan201
Internet        82   000f.2034.4b32  ARPA   Vlan201
Internet        83   0014.c20a.11c3  ARPA   Vlan201
Internet        89   000d.9d99.12f4  ARPA   Vlan201
Internet        89   000f.20fd.4973  ARPA   Vlan201
Internet 4   000f.2034.4b2f ARPA   Vlan201
Internet        89   000f.fe9d.976d  ARPA   Vlan201
Internet        86   000f.fe40.d64b  ARPA   Vlan201
Internet         0   000f.fec8.6605  ARPA   Vlan201
Internet        89   0014.c20c.89f5  ARPA   Vlan201

Using include Vlan201 I cut the list to the single VLAN that connect to my 2960 switch, it is a good way to shorten the long list of every device in the network.
You can see that MAC 000f.2034.4b2f match the IP and all I have to do now is run nslookup and get the machine name.

  1. Roland
    May 24, 2010 at 2:44 pm

    Or you can download FREE switch port mapper here:


    It has built-in dns name resolution, very useful.



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