The Address Resolution Protocol, maps Ethernet addresses to IPv4 addresses and back.
A host that needs to transmit data to another host on the local Ethernet first broadcasts an Ethernet request asking “Which MAC address is responsible for this IP address?” These ==broadcasts go to all hosts attached to that Ethernet network.==
ARP Cache
When a host maps a MAC address to an IP address, it caches that information in the ARP table for a few minutes.
Once the cache entry expires, it re-queries the network via ARP.
The better failover implementations send an unrequested gratuitous ==ARP message to announce the new MAC address for an IP address.==
Command to view a host’s ARP table :
arp -a
If a host doesn’t have an ARP entry, your host either hasn’t communicated with that host before, or the target host’s ARP cache entry has expired.
If only address filter is requested, the IP address can be added after arp -a.