Troubleshooting – Finding Laptop with only the DNS Name

Finding the switch port that a laptop is connected to with just its DNS name requires a few more steps compared to knowing the IP address. Here’s how you can do it:

1. Resolve the DNS Name to an IP Address:

First, you need to translate the DNS name into an IP address. You can do this using the ‘nslookup’ command in the command line (on a Windows machine) or terminal (on a Unix-like machine).

On Windows, open a command prompt and enter:

nslookup <laptop's DNS name>

On Unix-like systems, open a terminal and enter:

dig +short <laptop's DNS name>

The output will give you the IP address associated with the DNS name.

2. Identify the MAC address of the laptop:

Once you have the IP address, log into your router and enter the command:

show ip arp | include <laptop's IP address>

This will output the MAC address associated with the IP address you found earlier.

3. Find the port where the laptop is connected:

With the MAC address, you can then log into the switch and enter the command:

show mac address-table address <laptop's MAC address>

or, depending on the IOS version:

show mac-address-table address <laptop's MAC address>

The output will include the port where the laptop is connected.

These steps assume you have access to both the router and the switch, and that you’re using Cisco IOS. The exact commands can vary depending on the specific Cisco equipment and software version.