[cisco-voip] Serial interface state change

[Fred Hunt]

I'm trying to figure out why a serial interface seemingly changed its state on its own.

We have a PRI that we are planning to decommission.  I previously removed it from being routed to in CUCM and I shut down the serial0/0/0:23 interface, as shown in the log below:
021241: Mar 16 20:32:48.963 CDT: %ISDN-6-LAYER2DOWN: Layer 2 for Interface Se0/0/0:23, TEI 0 changed to down
021242: Mar 16 20:32:50.960 CDT: %LINK-5-CHANGED: Interface Serial0/0/0:23, changed state to administratively down

Then, somehow the serial interface changed its state back to up.  This occurred after what appeared to be a brief outage of the T1 service.  Here's the relevant log detail:
021244: Mar 18 10:25:16.673 CDT: %CONTROLLER-5-UPDOWN: Controller T1 0/0/0, changed state to down (AIS detected)
021245: Mar 18 10:25:16.881 CDT: %MARS_NETCLK-3-HOLDOVER: Entering Holdover for Controller T1 0/0/0
021246: Mar 18 10:25:18.673 CDT: %LINK-3-UPDOWN: Interface Serial0/0/0:23, changed state to down
021247: Mar 18 10:25:20.673 CDT: %CONTROLLER-5-UPDOWN: Controller T1 0/0/0, changed state to up
021248: Mar 18 10:25:22.189 CDT: %LINK-3-UPDOWN: Interface Serial0/0/0:23, changed state to up
021249: Mar 18 10:25:23.133 CDT: %MARS_NETCLK-3-HOLDOVER: Exiting Holdover for Controller T1 0/0/0
021250: Mar 18 10:25:24.917 CDT: %ISDN-6-LAYER2UP: Layer 2 for Interface Se0/0/0:23, TEI 0 changed to up

Today, I discovered that the interface was up and shut it down again.  Then I decided to shutdown the controller itself.  Here's the log:
021310: Apr 10 13:57:23.272 CDT: %LINK-5-CHANGED: Interface Serial0/0/0:23, changed state to administratively down
021312: Apr 10 14:13:28.404 CDT: %CONTROLLER-5-UPDOWN: Controller T1 0/0/0, changed state to administratively down
021313: Apr 10 14:13:28.424 CDT: %MARS_NETCLK-3-HOLDOVER: Entering Holdover for Controller T1 0/0/0
021314: Apr 10 14:13:30.404 CDT: %LINK-3-UPDOWN: Interface Serial0/0/0:23, changed state to down

I observed that after shutting the controller down the state of serial0/0/0:23 changed from administratively down to down.  I'm guessing that this will stick now, but I'm not sure after the earlier behavior.  I don't understand how the serial interface was able to previously change its layer 1 state on its own.  Don't both administratively down and down mean down at the layer 1 level?  Does a router automatically reset the state of serial interfaces if their associated T1 controller changes from the down to up state?

Thanks,
Fred
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://puck.nether.net/pipermail/cisco-voip/attachments/20130410/703b8baf/attachment.html>