(InARP) Additions to arp typically used for frame relay.

frame relay stations route frames of a higher level protocol between lans, across a permanent virtual circuit. These stations are identified by their data link control identifier (DLCI), equivalent to an ethernet address in a lan itself.

InARP allows a station to determine a protocol address (e.g. ip address) from a DLCI. This is useful if a new virtual circuit becomes available. Signalling messages announce its DLCI, but without the corresponding protocol address it is unusable: no frames can be routed to it.

reverse arp (RARP) performs a similar task on an ethernet lan, however RARP answers the question "What is my IP Address?" whereas InARP answers the question "What is your protocol address?".

See rfc 2390.