Isdn backup invoked without an apparent reason

[Philidor]

Backup router log is showing isdn activities occurred on today and yesterday, while last time main link flapped occurred on Sep 17th

Sep 18 03:19:40.219 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 68 changed to up
Sep 18 03:19:54.934 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 68 changed to down
Sep 18 03:47:40.277 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 69 changed to up
Sep 18 03:47:54.941 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 69 changed to down
Sep 18 10:29:40.392 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 70 changed to up
Sep 18 10:29:54.920 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 70 changed to down
Sep 18 10:57:40.406 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 71 changed to up
Sep 18 10:57:54.918 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 71 changed to down
Sep 18 17:31:40.576 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 72 changed to up
Sep 18 17:31:54.910 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 72 changed to down
Sep 18 17:49:52.914 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 73 changed to up
Sep 18 17:50:04.918 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 73 changed to down
Sep 18 17:59:40.590 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 74 changed to up
Sep 18 17:59:54.902 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 74 changed to down
Sep 19 00:41:40.716 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 75 changed to up
Sep 19 00:41:54.887 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 75 changed to down
Sep 19 01:11:40.758 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 76 changed to up
Sep 19 01:11:54.882 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 76 changed to down
Sep 19 07:43:40.898 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 77 changed to up
Sep 19 07:43:54.862 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 77 changed to down
Sep 19 08:11:40.906 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 78 changed to up
Sep 19 08:11:54.862 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 78 changed to down
Sep 19 14:41:41.005 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 79 changed to up
Sep 19 14:41:54.845 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 79 changed to down
Sep 19 15:03:40.958 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 80 changed to up
Sep 19 15:03:54.842 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 80 changed to down
backup# sh clock
15:26:33.144 CET Mon Sep 19 2022

Sep 17 18:07:50.586: %LINK-3-UPDOWN: Interface Serial0/1/0, changed state to down
Sep 17 18:07:50.586: %FR-5-DLCICHANGE: Interface Serial0/1/0 - DLCI 50 state changed to DELETED
Sep 17 18:07:51.586: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1/0, changed state to down
Sep 17 18:07:58.661: %LINK-3-UPDOWN: Interface Serial0/1/0, changed state to up
Sep 17 18:07:58.661: %FR-5-DLCICHANGE: Interface Serial0/1/0 - DLCI 50 state changed to ACTIVE
Sep 17 18:07:59.661: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1/0, changed state to up
Main#sh clock
15:27:15.843 NFT Mon Sep 19 2022

[marce1000]

 - Review these bug reports : https://bst.cloudapps.cisco.com/bugsearch?pf=prdNm&kw=ISDN-6-LAYER2DOWN&bt=custV&sb=anfr , check if any of them could  be related to your equipment.

 M.

[mlund]

Hi

20 years since I worked with isdn, but in my mind I think "debug dialer" will give you the reason.

/Mikael

[Georg Pauwen]

Hello,

can you post a diagram of your topology, showing how your devices are connected ? How is the ISDN backup triggered ?

[Philidor]

I previously attached a couple of files with pieces of config of the main and backup router. By the way, both the routers are connected to a common switch.

aitan8o6ap#sh stand
Ethernet0 - Group 1
Local state is Standby, priority 100, may preempt
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.943
Virtual IP address is 10.139.148.129 configured
Active router is 10.139.148.131, priority 110 expires in 7.376
Standby router is local
4 state changes, last state change 3w6d
IP redundancy name is "hsrp-Et0-1" (default)

Sep 21 09:31:54.715 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 93 changed to down
Sep 21 15:59:54.971 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 94 changed to up
Sep 21 16:00:09.707 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 94 changed to down
Sep 21 16:13:41.854 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 95 changed to up
Sep 21 16:13:54.694 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 95 changed to down
Sep 21 16:39:41.536 CET: ISDN Recvd L1 prim 1 dsl 0 state 3 ctrl_state 0
Sep 21 16:39:41.568 CET: ISDN BR0: L1 is IF_ACTIVE
Sep 21 16:39:41.576 CET: ISDN BR0 EVENT: isdn_sw_cstate: State = 4, Old State = 4
Sep 21 16:39:41.616 CET: ISDN BR0: Incoming call id = 0x00D4, dsl 0
Sep 21 16:39:41.820 CET: ISDN BR0: TX -> IDREQ ri=3699 ai=127
Sep 21 16:39:41.900 CET: ISDN BR0: RX <- IDASSN ri=3699 ai=96
Sep 21 16:39:41.932 CET: ISDN BR0: TX -> SABMEp c/r=0 sapi=0 tei=96
Sep 21 16:39:41.948 CET: ISDN BR0: RX <- UAf c/r=0 sapi=0 tei=96
Sep 21 16:39:41.952 CET: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0, TEI 96 changed to up
Sep 21 16:39:51.964 CET: ISDN BR0: TX -> RRp sapi=0 tei=96 nr=0
Sep 21 16:39:51.980 CET: ISDN BR0: RX <- RRf sapi=0 tei=96 nr=0
Sep 21 16:39:54.692 CET: ISDN BR0: RX <- DISCp c/r=1 sapi=0 tei=96
Sep 21 16:39:54.696 CET: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0, TEI 96 changed to down
Sep 21 16:39:54.700 CET: ISDN BR0: TX -> UAf c/r=1 sapi=0 tei=96
Sep 21 16:40:04.828 CET: ISDN Recvd L1 prim 5 dsl 0 state 1 ctrl_state 0
Sep 21 16:40:04.836 CET: ISDN BR0: Recvd MPH_EI1_IND from L1
Sep 21 16:40:06.368 CET: ISDN Recvd L1 prim 3 dsl 0 state 2 ctrl_state 0
Sep 21 16:40:06.380 CET: ISDN BR0 EVENT: isdn_sw_cstate: State = 0, Old State = 4
Sep 21 16:40:06.452 CET: ISDN BR0: Physical layer is IF_DOWN
Sep 21 16:40:06.468 CET: ISDN BR0: Shutting down ME
Sep 21 16:40:06.504 CET: ISDN BR0: Shutting down ISDN Layer 3