What is the arp command used for?

arp -a lists the IP-to-MAC address bindings currently in the host's ARP cache (recently accessed devices only).

The arp Command:

The arp command is executed from the Windows, Linux, or Mac command prompt.

Purpose:

• Lists all devices currently in the ARP cache of the host
• Displays the known IP address and MAC address binding

Command:

arp -a

Important notes:

• The ARP cache only displays information from devices that have been recently accessed
• To ensure the ARP table is populated, ping a device first so it will have an entry in the ARP table

Clearing the ARP cache:

# Windows (admin required)
netsh interface ip delete arpcache

Use case: Network administrators may want to clear the cache and repopulate it with updated information.

Note: You may need administrator access on the host to use the netsh interface ip delete arpcache command.

Go deeper:

• Wikipedia — Address Resolution Protocol (ARP) — how the IP-to-MAC bindings arp -a lists get created and cached in the first place.