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

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

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.

Diagram showing the network architecture of a Cisco switch with devices connected to ports Gi1/0/1 and Gi1/0/2, including their IP and MAC addresses.

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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