Hi every body.
I have few questions about LMI inquiry and status messages.
Who sends inquiry message? Is it router connected to frame relay switch?
Thanks a lot.
actually the FR switch answers with two types of messages:
every 10 seconds with a status message
every 60 seconds instead of sending a status message it sends a full status message with all the info about the known DLCIs and their state.
Someone may call keepalives the status messages to distinguish them from full state messages.
you can see this on the debug output attached by Jerry on the router side
Aug 26 02:29:18.142: Serial0/0/0(in): Status, myseq 1, pak size 45
*Aug 26 02:29:18.142: RT IE 1, length 1, type 0
*Aug 26 02:29:18.142: KA IE 3, length 2, yourseq 1 , myseq 1
*Aug 26 02:29:18.142: PVC IE 0x7 , length 0x6 , dlci 301, status 0x0 , bw 0
*Aug 26 02:29:18.142: PVC IE 0x7 , length 0x6 , dlci 302, status 0x0 , bw 0
*Aug 26 02:29:18.142: PVC IE 0x7 , length 0x6 , dlci 304, status 0x0 , bw 0
*Aug 26 02:29:18.142: PVC IE 0x7 , length 0x6 , dlci 305, status 0x0 , bw 0
this is the full status message describing the state of four DLCIs but it sent every 60 seconds.
Shorter status messages are sent every 10 seconds.
Then, as Lucien has noted also there are the end-to-end keepalives but going from DTE to DTE these are not LMI.
Hope to help
Historically, it was LMI performing keepalive.
Then appeared a the end to end keepalive feature which is exchanged over LMI protocol.
A good reading for this is the following book:
And also you can read:
The end-point (router) will send the enquiry message to the FRSW, and the FRSW will reply with the status message. These message will repeat in an interval to perform keepalive.
FR LMI messages means to exchange information between Router and FR switch about the link and the status of PVC connectivity. These messages serve as kind of keepalives for the frame connection. If keepalives are not continually received by both Router and FR switch, the frame connection will drop.
So both end- Router as well as FR switch exchange LMI messages.
Refer this link for more inforamtion:
You can view this communication by debuging the LMI messages (debug frame-relay lmi) on your router. You may need to wait for a while to view these messages. It should look like this
: Serial1(in): Status, myseq 4
: RT IE 1, length 1, type 0
: KA IE 3, length 2, yourseq 5 , myseq 4
: PVC IE 0x7 , length 0x3 , dlci 300, status 0x0
The router sends out LMI status enquiries to the Frame Relay switch in an attempt to determine an LMI type supported by the switch. This is indicated by the observation of StEnq in the debugs. The status reply message returned by the switch carries information on the supported LMI type, as well as the status of active permanent virtual circuits (PVCs). A successful exchange of LMI status messages with the Frame Relay switch increments the LMI sequence counter on the router.
Following information are reported in these messages
1) Number of keepalive exchanged.
2) DLCI number. This DLCI number should match your configuration.
3) Status of the DLCI. Active DLCI reported with 0x2
Any other status represent abnormal operation on service provider side.