ARP (Address Resolution Protocol)

ARP, Address Resolution Protocol, is a computer networking protocol for determining a network host's link layer or hardware address when only its Internet Layer (IP) or Network Layer address is known.

In Ethernet network, packets use MAC address for transmission, but in TCP/IP network, each packet uses IP address for transmission. So we need a policy for address resolution. ARP is most frequently used to translate IP addresses to Ethernet MAC addresses. Each station will have an ARP Table in its ARP Cache. The table uses for recording IP address and MAC address.[1]


延伸閱讀：
RARP、PROXY ARP
ARP 的詳細資料可以查詢 RFC-826﹑RFC-814﹑以及 RFC-1166 等文件。而 RARP 的資料則可以參考 RFC-903﹑RFC-906﹑還有 RFC-1293 等文件。[2]

References:
[1]http://en.wikipedia.org/wiki/Address_Resolution_Protocol
[2]http://www.pcnet.idv.tw/pcnet/network/network_ip_arp.htm