ISDN Layer 2 NOT activated

Unanswered Question
Apr 29th, 2010
User Badges:

Hi, can anyone suggest some help with this, I am an ISDN 2


When connected to our BRI and do a 'sh isdn stat' I get:

ISDN BRI0/1/1 interface
        dsl 3, interface ISDN Switchtype = basic-net3
    Layer 1 Status:
    Layer 2 Status:
        Layer 2 NOT Activated
    Layer 3 Status:
        0 Active Layer 3 Call(s)
    Active dsl 3 CCBs = 0
    The Free Channel Mask:  0x80000003
    Total Allocated ISDN CCBs = 0

Debug ISDN q921 gives me:

000587: Apr 29 05:20:40.322: BRI0/1/1: In state F7, Received code unknown code
000588: Apr 29 05:20:40.322: BRI0/1/1: In state F7, Received code Activation Indication with

Priority to 8, Info 4 received

000589: Apr 29 05:20:40.322: BRI0/1/1 : do nothing

And when I try a call to one of the numbers I see:

001234: Apr 29 05:40:23.854: ISDN BR0/1/0 Q921: User RX <- SABMEp sapi=0 tei=0
001235: Apr 29 05:40:24.862: ISDN BR0/1/0 Q921: User RX <- SABMEp sapi=0 tei=0
001236: Apr 29 05:40:25.874: ISDN BR0/1/0 Q921: User RX <- SABMEp sapi=0 tei=0

The interface config is:

interface BRI0/1/0
description ISDN 2 xxxxxxxxx
no ip address
isdn switch-type basic-net3
isdn overlap-receiving
isdn incoming-voice voice
trunk-group PSTN
no clns route-cache

I know the line works because it is normaly connected to an ISDN modem but we are trying to migrate to this new router.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (2 ratings)
rdessert Thu, 04/29/2010 - 12:49
User Badges:

Hi Drew,

What country is the ISDN circuit and router in?

What type of interface do you have in the router U, or S/T?  You can check this by looking at the output of the "sh int bri0/1/1" command towards the top.

In North America, if the router's BRI interface is a U interface, it can be directly connected to the telco jack. In the rest of the world, where the Network terrmination 1 (NT-1) is built into the telco network, the router S/T interface is directly connected to the telco jack.

In North America, if you have a BRI S/T interface you are required to use an external NT-1 (modem).
drewhughes Fri, 04/30/2010 - 05:05
User Badges:

Thanks for the replies, the router and circuit are in the UK.

The interface reports as ' Hardware is Voice NT or TE BRI' I didn't see anything about U or S/T

I don't get anything from debug q931!

Any ideas?

rdessert Fri, 04/30/2010 - 05:59
User Badges:

The output of "show diag" should also tell you if it is a U or an S/T

ISDN card.  For the UK and Europe you will need

an S/T which requires an external NT-1, typically provided by the phone company.

paolo bevilacqua Fri, 04/30/2010 - 06:19
User Badges:
  • Super Gold, 25000 points or more
  • Hall of Fame,

    Founding Member

rdessert, voice BRI interfaces are exclusively made with S/T interface.

Beside that, and interface with wrong type would never receive any frame as in the output above.

The problem can be due to bad cabling or buggy IOS.

shailesh.h Fri, 04/30/2010 - 09:26
User Badges:
  • Bronze, 100 points or more

Source of Layer 2 Problems often cannot be rectified at the customer site. However, Layer 2 debugs (or the interpretation of the debugs) can be provided to the telco for their reference. Hope you have asked BT or your service provider the type of ISDN switch..

  1. Now connect one of the telephone to ISDN Modem (if it is BRI) and check for dialtome and incoming and outgoing calls -- if this is successful then. If this is not happening then check for cabling or get it corrected through service provider
  2. Connect to router and give incoming call to the number (put debug command on) - Share the output.

Reference document is


This Discussion