Useful macOS network terminal commands – An introduction to ARP scan

In this video we take a look at a terminal command that will allow us to view the IP and MAC addresses being used by devices on our home network. As an IP address can be considered to be like a devices telephone number, and the MAC address like its name. We can use ARP to help identify devices on our home network.

ARP or Address Resolution Protocol is a procedure for mapping dynamic IP addresses to their associated MAC address. A MAC address is simply a unique address assigned to a devices network adapter. So through the ARP command, we can query the mapping between these pieces of information.

This makes the ARP command a useful tool for querying what is connected to a network. For example, in order to connect to a Synology NAS, we need to know the IP address that it is using. So as long as we know the MAC address of our NAS, we can use the ARP command to find its IP address.

Quick reference notes:

  • Open the Terminal application found in the Utilities folder within Applications
  • Type the following 
arp -a
  • After completing your test you can end your Terminal session by typing.
exit

Reference Material:

Wikipedia article – Terminal (macOS)
Apple article – Terminal User Guide for Mac

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