T1: A Survival Guide

The Local Management Interface

Network management was conspicuously absent from the first round of frame relay standards. However, the lack of network-management features stunted the growth of frame relay, so the major equipment vendors devised a specification for the Local Management Interface (LMI), which eventually became known as the “Gang of Four” LMI.^[22] LMI has three main tasks: link integrity verification, PVC status reporting, and PVC notification.

Warning

In many cases, LMI monitoring extends only to the local switch. It does not provide end-to-end status monitoring. If the frame relay network fails, LMI will not mark any PVCs as down because it is monitoring only between your router and the edge of the frame relay cloud. With all PVCs reported as active, dial-backup solutions will not kick in. To provide dial-backup, you must run a routing protocol over the PVC.

LMI Annex G provides end-to-end monitoring, but the catch is defining what is meant by the end of a network. frame relay networks often use ATM backbones for transporting frames across wide areas, and the end of a PVC may be either the other end of the virtual circuit or the interface between the frame relay network and the ATM backbone. To be safe, you need to run a routing protocol for each network layer.

Complementary technology addressed LMI’s limitations, and LMI became a great success. Standards organizations enhanced it, but caused a fork in the specification as part of the process. Three main LMI types ...