Loopback on T1

Unanswered Question
Apr 4th, 2007

Hi there,

I got 4 new 1841 with a T1 WIC. I have configured the F0/0, S0/0/0 (Frame-Realy), and the sub-int S0/0/0.1 correctly. I would like to know why when I do a show ip interface breif, the S0/0/0 and S0/0/0.1 status come up as Down and the protocol as down. I understand that the protocol would show the protocol as down since I haven't plugged the T1 to the jack.

Also, what does the loopback button on the WIC card do?

Thanks in advance,


I have this problem too.
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situwayne Wed, 04/04/2007 - 09:39

Push this button to place the WIC into loopback mode. The service provider can send a signal to test the connection from your site to the central office switch.

Push this button again to turn off loopback mode.

skhirbash Wed, 04/04/2007 - 09:55

Thanks for answering the second part of my inquiry. Can someone kindly answer the first part of my question?

Thanks in advance,


skhirbash Wed, 04/04/2007 - 10:01

Shouldn't I see the status of the serial inteface (and sub-interface) as being "UP" after configuring it properly and executing the "no shutdown" command? I am seeing the status as being "UP" for the Fastethernet! Keep in mind that I still haven't plugged in the T1 WIC to the T1 jack.

skhirbash Wed, 04/04/2007 - 11:10

Sorry, but I can't access the link mentioned as I don't currently have a privilaged cisco account.

skhirbash Wed, 04/04/2007 - 11:12

After I have pressed the Loopback button, the "AL" and "LP" LEDs light up solid amber and when I pressed the button again the "LP" LED disappeared but not the "AL". What is this "AL" and how do I get rid of it?



situwayne Wed, 04/04/2007 - 11:21

you have an "alarm" condition. make sure your circuit and patch cord is ok.

skhirbash Wed, 04/04/2007 - 11:41

Nothing is plugged into the WIC card yet. I removed the WIC card and plugged it back in and that seemed to have corrected the problem; however, once I reload or recycle the device, the "AL" amber light comes back on. Any ideas?

Thanks again in advance,


situwayne Wed, 04/04/2007 - 12:44

here is what i think is happening....your WIC is not connected to an active circuit and you did "no shut" on the serial interface. because there is no carrier detected you get an alarm.

you can make a T1 loopback plug and see if the alarm goes away.

to make a T1 loopback plug, use a RJ-45 connector and wire as follow

1 > 4

2 > 5

skhirbash Mon, 04/09/2007 - 21:35

That worked!

Great and thanks for all of your assitance.



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