Frame relay address mapping
Frame relay address mapping associates the protocol address of a remote device with its frame relay address (local DLCI) so the upper layer protocol, IP for example, can locate the remote device.
Take delivering an IP packet across a frame relay network for example. After a DTE device receives an IP packet, it looks up the IP routing table for the outgoing interface and next hop address. If the outgoing interface is enabled with frame relay, the device must look up the frame relay address mapping table based on the next hop IP address for the DLCI.
The address mappings can be static ones administratively created or dynamic ones created with the InARP.
The following describes how frame relay uses InARP to create an address mapping:
Once a new virtual circuit is created, InARP sends an InARP request over the circuit to request the peer end for its protocol address. This request also conveys the local protocol address. When the peer device receives the request, it creates an address mapping based on the protocol address in the request and responds with its protocol address. When the local end receives the response, it creates the address mapping for the peer.
For virtual circuits with static address mappings, InARP will not be performed whether or not the mappings are correct. In addition, the InARP request recipient does not create a mapping based on the protocol address in the request if a static entry is already available for the address.
In an IPv6 network, address mappings are dynamically maintained by Inverse Neighbor Discovery (IND). IND works in the same way InARP works.