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Bronze

lmi messages in frame relay

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.

4 ACCEPTED SOLUTIONS

Accepted Solutions
Bronze

Re: lmi messages in frame relay

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:

http://www.cisco.com/en/US/tech/tk713/tk237/tsd_technology_support_protocol_home.html

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.

Cisco Employee

Re: lmi messages in frame relay

Hi Sarah,

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.

http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1918.html#wp1020616

"

Re: lmi messages in frame relay

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:

http://books.google.com/books?id=GPuhnmjxLuQC&pg=PA195&lpg=PA195&dq=frame+relay+lmi+keep+alive&source=bl&ots=dhzqGX2mWo&sig=RfX5-J6zCviJMSQnKlEG5BjuQhI&hl=en&ei=kduUSuOiKpCasgPdrfDsCA&sa=X&oi=book_result&ct=result&resnum=4

And also you can read:

http://www.ciscopress.com/articles/article.asp?p=170741&seqNum=3

Hall of Fame Super Silver

Re: lmi messages in frame relay

Hello Sarah,

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.

Edit:

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

Giuseppe

5 REPLIES
Bronze

Re: lmi messages in frame relay

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:

http://www.cisco.com/en/US/tech/tk713/tk237/tsd_technology_support_protocol_home.html

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.

Cisco Employee

Re: lmi messages in frame relay

Hi Sarah,

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.

http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1918.html#wp1020616

"

Bronze

Re: lmi messages in frame relay

Thanks Jerry.

"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."

So there are two messages i.e status inquiry and status message. These messages also perform the function of keepalive.

But in the link, i found:

"Keepalives (messages sent through a connection to ensure that both sides will continue to regard the connection as active) and PVC status messages are examples of these messages and are the common LMI features that are expected to be a part of every implementation that conforms to the consortium specification"

Based on the above, it appears there is status message called keep alive.

Or

These status inquiry and status message together also perform keepalive funtion.

Thanks a lot.

Re: lmi messages in frame relay

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:

http://books.google.com/books?id=GPuhnmjxLuQC&pg=PA195&lpg=PA195&dq=frame+relay+lmi+keep+alive&source=bl&ots=dhzqGX2mWo&sig=RfX5-J6zCviJMSQnKlEG5BjuQhI&hl=en&ei=kduUSuOiKpCasgPdrfDsCA&sa=X&oi=book_result&ct=result&resnum=4

And also you can read:

http://www.ciscopress.com/articles/article.asp?p=170741&seqNum=3

Hall of Fame Super Silver

Re: lmi messages in frame relay

Hello Sarah,

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.

Edit:

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

Giuseppe

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