Local Management Interface
Local Management Interface (LMI) messages manage the local access link between the router and
the Frame Relay switch. A Frame Relay DTE can send an LMI Status Enquiry message to the
switch; the switch then replies with an LMI Status message to inform the router about the DLCIs
of the defined VCs, as well as the status of each VC. By default, the LMI messages flow every
10 seconds. Every sixth message carries a full Status message, which includes more complete
status information about each VC.
The LMI Status Enquiry (router) and Status (switch) messages function as a keepalive as well.
A router considers its interface to have failed if the router ceases to receive LMI messages from
the switch for a number (default 3) of keepalive intervals (default 10 seconds). As a result, FR LMI
is actually enabled/disabled by using the keepalive/no keepalive interface subcommands on a
Frame Relay interface.
Three LMI types exist, mainly because various vendors and standards organizations worked
independently to develop Frame Relay standards. The earliest-defined type, called the Cisco LMI
type, differs slightly from the later-defined ANSI and ITU types, as follows:
■ The allowed DLCI values
■ The DLCI used for sending LMI messages
Practically speaking, these issues seldom matter; by default, routers autosense the LMI type. If
needed, the frame-relay lmi-type type interface subcommand can be used to set the LMI type on
the access link. Table 15-2 lists the three LMI types, the type keyword values, along with some
comparison points regarding LMI and permitted DLCIs.
Frame Relay LMI Types
LMI Type Source Document
Cisco IOS lmi-type
Parameter
Allowed DLCI Range
(Number)
LMI
DLCI
Cisco Proprietary Cisco 16–1007 (992) 1023
ANSI T1.617 Annex D Ansi 16–991 (976) 0
ITU Q.933 Annex A q933a 16–991 (976) 0