Is the BRI d-channel active or not??

jeff.bankston · ‎05-14-2004

What's the best way to determine if the d channel in a bri connection is active? I'm using bri as a DDR to a frame circuit by using the "backup interface" command on the subif pointing to my bri1/1. The DDR backup function is working fine.

The question is - our noc needs to monitor the d channel to determine that the bri is functioning. I telnetted to the remote site and a "show isdn stat" shows that the bri1/1 is layer 2 "ESTABLISH_AWAITING_TEI" condition. Should the frame connection fail, bri1/1 dials properly so the actual operation of the DDR is not in question. Just how to tell if the d-channel is operative while the bri1/1 is in standby mode.

Thanks, Jeff

zahmed · ‎05-16-2004

You would have to do some SNMP stuff to get that info via CISCO-ISDN-MIB :

http://www.cisco.com/pcgi-bin/Support/Mibbrowser/mibinfo.pl?mn=CISCO-ISDN-MIB

Object you need to poll might be : isdnLapdOperStatus

http://www.cisco.com/pcgi-bin/Support/Mibbrowser/unity.pl?f=Translate&t=no&o=isdnLapdOperStatus

Some SNMP expert might shed further light on that.

~Zulfi

jeff.bankston · ‎05-17-2004

that's great for snmp, thanks, but how about from the command prompt? Is ESTABLISH_AWAITING_TEI sufficient to say the d channel is up?

Thanks, Jeff

jolmo · ‎05-17-2004

I'm not sure but I don't think so. Layer 2 state should be MULTIPLE_FRAME_ESTABLISHED.

About ESTABLISH_AWAITING_TEI state:

"These states are often temporary. Use the command clear interface bri number to restablish Layer 2 connectivity. If those states persist for extended periods use the debug isdn q921 command for further troubleshooting"

There are a good couple of links for troubleshooting Layer 2 BRI:

http://www.cisco.com/en/US/tech/tk801/tk379/technologies_tech_note09186a0080094b77.shtml

http://www.cisco.com/en/US/tech/tk801/tk379/technologies_tech_note09186a0080094b78.shtml

HTH

Richard Burts · ‎05-17-2004

MULTIPLE_FRAME_ESTABLISHED is the goal when the interface is active and the advice about clearing the interface if the state is other than MULTIPLE_FRAME_ESTABLISHED is based on the assumption that the interface is attempting to be active. However with "backup-interface" the router inhibits communication on the backup interface unless the primary is down.

The suggestion about using debug isdn q921 might be helpful. It will tell you whether there is communication between the router and the ISDN switch. I have not tested this but I suspect that you will find that there is no communication with the ISDN switch while the primary interface is active.

In my experience using ISDN backup, if we wanted to verify functionality of the ISDN we either forced an error on the primary interface (shutdown will not do what you want for this) or we removed the backup-interface paramater on the primary to allow the ISDN to establish communication.

I am not sure that it is possible to get an accurate assessment of the state of the D channel while the interface is in backup state.

HTH

Rick

jeff.bankston · ‎05-17-2004

Great, thanks. Yours and the post just before it pretty much told me what I wanted to know, that the NOC is hosed up if they wanted to see an active d channel but inactive B channels while in the backup interface's standby mode.

It works quite well, I've already proved that and it performed perfectly.

Thanks, Jeff

makchitale · ‎05-17-2004

As soon as we put the physical BRI interface as a backup, the isdn layer1 should get DEACTIVATED.

isdn2-2#sh isdn sta

Global ISDN Switchtype = basic-5ess

ISDN BRI0 interface

dsl 0, interface ISDN Switchtype = basic-5ess

Layer 1 Status:

ACTIVE

Layer 2 Status:

TEI = 64, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x80000003

Number of L2 Discards = 52, L2 Session ID = 171

Total Allocated ISDN CCBs = 1

isdn2-2#conf t

Enter configuration commands, one per line. End with CNTL/Z.

isdn2-2(config)#int e0

isdn2-2(config-if)#back int br0

isdn2-2(config-if)#

15w3d: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BRI0, TEI 64 changed to down

15w3d: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 64 changed to down

15w3d: %LINK-5-CHANGED: Interface BRI0, changed state to standby mode

15w3d: %LINK-3-UPDOWN: Interface BRI0:1, changed state to down

15w3d: %LINK-3-UPDOWN: Interface BRI0:2, changed state to down

isdn2-2#sh

15w3d: %SYS-5-CONFIG_I: Configured from console by consoleisdn sta

Global ISDN Switchtype = basic-5ess

ISDN BRI0 interface

dsl 0, interface ISDN Switchtype = basic-5ess

Layer 1 Status:

ACTIVATING

Layer 2 Status:

Layer 2 NOT Activated

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x0

Number of L2 Discards = 52, L2 Session ID = 171

Total Allocated ISDN CCBs = 1

isdn2-2#

isdn2-2#sh isdn sta

Global ISDN Switchtype = basic-5ess

ISDN BRI0 interface

dsl 0, interface ISDN Switchtype = basic-5ess

Layer 1 Status:

DEACTIVATED <==NOTE: L1 now gets DEACTIVATED (this test is on 12.1(18) & 12.2T latest)

Layer 2 Status:

Layer 2 NOT Activated

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x0

Number of L2 Discards = 52, L2 Session ID = 171

Total Allocated ISDN CCBs = 1

1-3-4-isdn2-2#sh int br0 | inc BRI0

BRI0 is standby mode, line protocol is down

This leaves us with two options to check the status of the BRI interface in backup state:

1) Periodically remove the backup command & ensure it comes out of the standby state & is back to the status of "MULTI_FRAME_EST".

2) Configure dialer profiles or dialer rotary groups, bind the physical BRI interface to the dialer & have the backup interface point to the dialer instead of the physical. This way we will always be able to see the status of the BRI interface (the dialer will be in STANDBY mode)