Before hosts can communicate with each other, the sending host on the same network as the receiving host must discover the hardware address of the receiving host.
Hardware addresses are unique numbers assigned to network interface boards by their manufacturers or by network administrators, such as 00:DD:A8:13:48:C5.
The Address Resolution Protocol (ARP) discovers the hardware address corresponding to a specific IP address and stores this mapping in the sending host's memory.
When a host receives data for a local IP address (an IP address on that physical network), it broadcasts an ARP request to all machines on the local network segment. This request message asks all machines if the IP address belongs to them. If the IP address belongs to a host on the local network segment, the machine adds its hardware address to the packet and returns the packet to the sender. The sender stores the mapping and uses it each time it sends data to that host.
Old mappings are deleted from the ARP cache automatically after a few minutes.
Cisco TCP/IP Suite for Windows supports two types of ARP translation assistance for systems not directly connected to networks with ARP capabilities:
Proxy translations let a machine on the physical network advertise its hardware address as that of another host.
Proxy translations require manual entry of the IP and hardware addresses if an interface that is not the active interface on the machine will handle the proxy translation and services for the other host.
Publish translations advertise the IP address and hardware address of a machine on a physical network that does not use ARP. The host that does not use ARP must be connected to the same network as the host supplying the publish translation.
The publish translation is manually entered; proper discovery of the IP and hardware addresses are the responsibility of the user.
HTML file generated May 15, 1996.