Compatible Systems 5.4 manual Appendices 293, Frame Relay Example

Appendices 293

Network/protocol addresses are associated with each PVC using one of two methods: static mapping, or the Inverse Address Resolution Protocol (IARP).

IARP is outlined in RFC 1293. IARP allows dynamic mapping of protocol addresses to a DLCI. It can be used for IP, IPX and AppleTalk. It is more flex- ible and easier to configure than static configuration.

IARP is used when a router discovers a new PVC with its corresponding DLCI on a physical interface. The PVC is discovered by communicating with the Frame Relay switch using the LMI protocol. This may be done when the router is coming up or when a PVC has come back up after going down for some reason.

A Frame Relay Example

The following diagram shows three remote office 56K Frame Relay connec- tions feeding one central office T1 connection. Note that the PVCs are shown as virtual point-to-point links which run through the physical connections and the Frame Relay cloud.

DLCI #72

T1 Connection		56K Connection
PVC A
DLCI #10
DLCI #11	PVC B	DLCI #72
DLCI #12
PVC C		56K Connection

Frame Relay Cloud

56K Connection

DLCI #10

A Frame Relay Example

The DLCI numbers in the diagram are only locally significant. That is, DLCI numbers can only be guaranteed to not be duplicated locally, and a DLCI at one location has no significance at another location.