Wide-Area Networks - CCIE Routing and Switching Exam Certification Guide - page 204

Frame Relay DLCI Figure 5-6

Router A Router B

DLCI 200

DLCI 400

DLCI 100

DLCI 400

DLCI 300

Frame Relay Network

DLCI 100

DLCI 100 DLCI 200

DLCI 400

DLCI 300

Router C Router D PVCs

The DLCI is configured for each interface or subinterface to mark the appropriate PVC. For
example, the following frame relay command configures DLCI 100 on interface serial 0.1:

interface serial 0.1 point-to-point
ip address 192.168.1.5 255.255.255.252
frame-relay interface-dlci 100

Frame Relay Inverse Address Resolution Protocol (InARP)
Frame Relay Inverse ARP maps remote protocol addresses to local DLCI numbers. It is on by
default and prevents the need to manually configure DLCI mappings in full mesh topologies
(multipoint). Inverse-ARP requests are sent on all VCs when a multipoint interface or VC
becomes active.

To configure Inverse ARP, use the frame-relay inverse-arp command.

To erase Inverse-ARP mappings, use the clear frame-relay inarp command.

Congestion Control
Frame Relay has few control and error mechanisms as compared with X.25, but these have been
sufficient, and in fact, contribute to the popularity of the protocol. The following are methods
that determine or reduce congestion and errors in the network:
•

Forward explicit congestion notification (FECN)

•

Backward explicit congestion notification (BECN)