What is ARP (Address Resolution Protocol)? This protocols main purpose is to identify network nodes MAC address using its IP. ARP creates database of discovered nodes in the network and saves it on local machine for future use.
Whenever one node of the network needs to know some other nodes MAC address, it broadcasts the ARP message to the network. Message contains required nodes IP address. When the node with requested IP receives message it replies with physical address.
As mentioned before, the MAC-to-IP mapping is saved on the hard drive of the machine in the ARP cache or ARP table form. Example of ARP table is shown in Figure 1.
Figure 1. ARP table on Windows machine
If the ARP requires the MAC address of the node it first checks the ARP table. If there is a mapping for the required IP, then there is no need for broadcasting a message to the network.
Table contains dynamic and static types of IP. Dynamic record is made when the data in ARP table is not satisfactory. Static records are only ones that have been input to the ARP table manually. It can be done using OS-specific ARP utility.
ARP is commonly used for networking troubleshooting and discovery of the machine with failure. It is also used for IP conflict resolution in the network.
