arp displays and modifies the kernel's ARP (Address Resolution Protocol) cache: the mapping between IP addresses on the local network and their hardware (MAC) addresses. It is part of the legacy net-tools package, now superseded by ip neigh.
arp -a # show all entries
arp -n # numeric (don't resolve names)
ip neigh # modern equivalent
Most administrators encounter arp only in older documentation or when diagnosing stale ARP entries on misbehaving switches. The command itself rarely does anything beyond what ip neigh offers.
Related terms: ip, net-tools
Discussed in:
- Chapter 12: Networking — Link Layer and ARP