Discover the device connected to a Layer 3 Cisco Switch Port using MAC Address to IP Address Mapping

Written by James McDonald

July 30, 2013

You need to ping the device from the switch so you can populate the switches arp cache with the IP/Mac mapping.

From there you can then find the port

# firstly on the cisco switch you need to ping the IP address of the device

ping 192.168.0.6
Sending 5, 100-byte ICMP Echos to 192.168.0.70, timeout is 2 seconds:

!!!!!

# you can grab the mac address connected to a cisco switch port

switch01#show mac-address-table | include Gi0/6
   1    d4be.d9fb.8630    DYNAMIC     Gi0/6

# and get the IP Address of the connected device
switch01#show ip arp | include d4be.d9fb.8630
Internet  192.168.0.6             0   d4be.d9fb.8630  ARPA   Vlan1

This may only work if the host you are trying to track down is doing inter-subnet communications.

You may need to do a ping or nmap -sP subnet/subnet_mask to populate the mac-address-table on the switch.

YMMV

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