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Address Resolution Protocol (ARP) is a low-level network protocol for translating network layer addresses into link layer addresses.
ARP lies between layers 2 and 3 of the OSI model, although ARP was not included in the OSI framework and allows computers to introduce each other across a network prior to communication.
Because protocols are basic network communication units, address resolution is dependent on protocols such as ARP, which is the only reliable method of handling required tasks.
When configuring a new network computer, each system is assigned an Internet Protocol (IP) address for primary identification and communication. A computer also has a unique media access control (MAC) address identity. Manufacturers embed the MAC address in the local area network (LAN) card. The MAC address is also known as the computer’s physical address.
Before two computers communicate, each must know the other’s relative IP or MAC addresses. If computer A only has computer B’s MAC address, computer A can reveal its IP address by sending an ARP request to computer B. Computer B may then reply by attaching its IP address with ARP to computer A. This simple address translation and exchange process is the primary role of ARP.
ARP tables can be stored to increase transmission rates by keeping track of addresses known to the network and transmitting any MAC or IP address changes via ARP.
There is no authentication required at this level, so spoofing of IP and MAC addresses is possible. Additional software may be required to police the ARP tables and prevent malicious user attacks.