What is arp

arp (address resolution protocol) is a commandline tool used to display and modify entries in the ARP cache on a system. ARP cache contains one or more tables which stores IP addresses and their associated physical addresses (MAC addresses).

An ARP entry will stay in the cache for 21600 seconds (6 hours) and will be deleted afterwards.

arp usage

Basic usage is the command with a option:

arp -a

The command above displays information on all hostname IP addresses, default gateway IP address, as well as the network broadcast’s one.

In order to delete an IP address from the ARP cache:

arp -d IP address

In order to add an IP address - MAC address mapping to ARP cache:

arp -s IP address MAC address

In order to clear the entire ARP cache:

apr -d