Frame Relay address mapping

Frame Relay address mapping associates the protocol address of a peer device with a Frame Relay address (local DLCI). Then, the upper-layer protocol, for example, IP, can locate the peer device.

For example, an IPv4 or IPv6 packet is transmitted across a Frame Relay network as follows:

1. When a DTE device receives an IPv4 or IPv6 packet, the DTE device looks up the IP routing table for the outgoing interface and next-hop address.

2. When the outgoing interface is enabled with Frame Relay encapsulation, the device looks up the next-hop address in the address-to-DLCI maps for the DLCI.

3. The packet is transmitted over the virtual circuit identified by the DLCI.

The address-to-DLCI maps include the following types:

• Static—Manually created.

• Dynamic—Created through InARP or Inverse Neighbor Discovery (IND).

Frame Relay uses InARP to create an address-to-DLCI map through the following process:

1. InARP sends an InARP request to the peer end through a virtual circuit at the InARP request interval during an InARP learning process when the following conditions exist:

   • A new virtual circuit is established.

   • The local interface is configured with an IPv4 address.

   The InARP request carries the local IPv4 address. By default, the InARP request interval during an InARP learning process (the detection timer) is 60 seconds.

2. When the peer device receives the InARP request, the peer device obtains the local IPv4 address and creates an address-to-DLCI map. At the same time, the peer device responds with an InARP reply carrying its IPv4 address.

3. When the local device receives the InARP reply, it creates an address-to-DLCI map.

4. After the local device creates the address-to-DLCI map, the local device modifies the InARP request interval to 12 minutes (the aging timer).

   The aging timer is fixed. When the aging timer expires, the local device continues to send InARP requests.

5. The local device sets the aging timer value to the detection interval when the following conditions exist:

   • The aging timer expires.

   • The local device has not received any InARP replies.

6. When the local device has not received any InARP replies within three detection intervals, the learned dynamic address-to-DLCI map is deleted.

   When the local device has not received InARP replies within a detection interval, the local device continues to send InARP requests. The local device stops sending InARP packets until the local interface is not configured with an IPv4 address or the local PVC is inactive.

IND creates IPv6 address-to-DLCI maps in a way similar to InARP.