Internet Core Protocols: The Definitive Guide

Variations on the ARP Theme

Just as an IP device can locate the hardware address for a specific IP address, so can a device locate the IP address associated with a known hardware address. Two variations on ARP take advantage of this capability, although for very different purposes:

Inverse ARP

Inverse ARP works exactly the opposite of regular ARP. Rather than a device needing to find the hardware address associated with a known IP address, Inverse ARP is used to find the IP address for a known hardware address.

Reverse ARP

Reverse ARP is used to allow a diskless workstation to request its own IP address, simply by providing its hardware address in an ARP request broadcast. A Reverse ARP server will see this request, assemble an ARP response that contains an IP address for the requester to use, and then send it back to the requesting device. The workstation will then use this IP address for its networking activity.

In addition, three other variations on ARP have been developed that attempt to overcome some of the problems that have proven to be common on IP networks:

DHCP ARP

DHCP ARP is used by devices that obtain an IP address using an address-allocation protocol such as DHCP. The purpose of DHCP ARP is to allow the device to probe the network for any other device that may be using the assigned IP address already, prior to actually trying to use the address. This process helps prevent problems with duplicate or overlapping address assignments, as the requester can just reject the ...