What is ARP?


ARP is a Network layer protocol to know MAC address from IP address.


To communicate with computers which are connected within a LAN, computers have to know the MAC address.

However IP address isn’t associated with MAC address automatically, so computer use ARP to know MAC address.

The detail of ARP

ARP have “ARP request” and “ARP reply”, and get MAC address by using these two packet.

For example, when the computer want to know the MAC address of IP address, ARP request are below.

Target IP address⇒

Target MAC address⇒0x0000.0000.0000


If the IP address of computer, which receive the APR request, is not, they throw away the packet.

When the Target IP address match my IP address, the computer return the ARP reply.


From the APR reply, switch can make ARP table which has the information of each IP address and MAC address.


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