How to know the ip address of the device connected to a physical interface

Last updated: Oct 4, 2024

In this article, we'll look at how to map the ip address of a device to the physical interface of a Cisco switch.

The operation will be carried out in two stages:
- First, we'll map the mac address to the physical port using the mac table.
- Then we'll use the arp table to map the mac address to the ip address.

Prerequisites: The switch must have an ip address assigned to the same vlan as the devices we want to know about. I'll also explain this step in the example below.

Network Architecture

Let's suppose we're in the case of the architecture below and we want to know which IP addresses are connected to interfaces Gi1/0/1 and Gi1/0/2.

Match IP addresses to physical ports

Configure the switch's IP address

Note: The switch address(es) must be in the same vlan as the devices we want to identify. In this example, all the devices to be identified are in vlan 1.

Configure switch vlan 1 interface:

switch01(config)# interface vlan 1
switch01(config-if)# ip address 192.168.1.1 255.255.255.0
switch01(config-if)# no shutdown

Get mac addresses

As explained above, switches are Layer 2 devices, so there's no way to retrieve this information directly with a single command; we first need to obtain the mac addresses of our devices, then search for them in the arp table.

So let's take a look at how to retrieve mac addresses connected to these two physical ports.

Obtain the mac address of the device connected to interface Gi1/0/1:

switch01# show mac address-table | include Gi1/0/1
   1    24b6.fd14.0853    DYNAMIC     Gi1/0/1

Obtain the mac address of the device connected to interface Gi1/0/2:

switch01# show mac address-table | include Gi1/0/2
   1    f8db.8845.ef15    DYNAMIC     Gi1/0/2

Note the informations retrieved:

Interface	mac address	ip address
Gi1/0/1	24b6.fd14.0853	-
Gi1/0/2	f8db.8845.ef15	-

Get ip addresses

Ping the IP addresses you wish to retrieve. This will populate the switch's arp table:

switch01# ping 192.168.1.200
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.200, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 36/51/74 ms

switch01# ping 192.168.1.210
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.210, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 33/48/71 ms

Display the arp table to match ip address with the mac address (use the “include” instruction to display only the line corresponding to our mac address):

switch01# show arp | include 24b6.fd14.0853
Internet  192.168.1.210              0   24b6.fd14.0853  ARPA   Vlan1

switch01# show arp | include f8db.8845.ef15
Internet  192.168.1.200              0   f8db.8845.ef15  ARPA   Vlan1

We can now deduce from this information that device 192.168.1.210 is connected to interface Gi1/0/1 and device 192.168.1.200 is connected to interface Gi1/0/2.

Interface	mac address	ip address
Gi1/0/1	24b6.fd14.0853	192.168.1.210
Gi1/0/2	f8db.8845.ef15	192.168.1.200

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