So you need to know a devices IP address and all you have is the MAC address. Or if you have the MAC but need the IP address. We’ll I’m here to tell you how to find the MAC or IP address of any machine in your Cisco network. First of all you’ll need access to the Layer two devices in your network, the switches.
coreswitch#show ip arp | i 10.80.211.14
Internet 10.80.211.149 140 000d.56ef.5f6b ARPA Vlan211
Internet 10.80.211.14 0 0006.5bb9.59f1 ARPA Vlan211
Use the one with the least age of “0”
Now take the mac address and find out what port the IP address was seen on by running the command “show mac-address-table | i 0006.5bb9.59f1”
coreswitch#show mac-address-table | i 59f1
211 0006.5bb9.59f1 dynamic Yes 0 Gi10/7
Now that you have port number run command “show cdp neighbors gigabitEthernet 10/7”
coreswitch#show cdp neighbors gigabitEthernet 10/7[/php][php]Device ID Local Intrfce Holdtme Capability Platform Port ID
DistroB1 Gig 10/7 150 S I WS-C2950G-Gig 0/1
Cool, now we have the Device ID of the distant end which is connected to the core switch and therefore brings us 1 hop closer to the device which we are looking for.
Take that device ID and use it to identify your next target switch. Login to that switch and run command “show mac-address-table | i 59f1 ”
DistroB1#show mac-address-table | i 59f1
211 4080.2111.4100 DYNAMIC Fa0/41
Fa0/41 is the port the device you are looking for is plugged into. You have just taken the ip address of a unknown device and found it in your network starting with your distrobution switch.