ARP

Address Resolution Protocol (ARP) is responsible for finding the MAC (hardware) address related to a specific IP address.

Each device within a network has a ledger to store information on, which is called a cache. In the context of ARP, this cache stores the identifiers of other devices on the network.

In order to map these two identifiers together (IP address and MAC address), ARP sends two types of messages:

1. ARP Request
2. ARP Reply
   When an ARP request is sent, a message is broadcasted on the network to other devices asking, “What is the mac address that owns this IP address?” When the other devices receive that message, they will only respond if they own that IP address and will send an ARP reply with its MAC address. The requesting device can now remember this mapping and store it in its ARP cache for future use.