serial port-line protocol donw

Unanswered Question
Jun 28th, 2008


I have connected wic-1t to an alcatel modem for a P2P link.

when i enter the no shut command under my serial interface.the link gets up but it will change to down after few seconds

any idea?

I have this problem too.
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Paolo Bevilacqua Sat, 06/28/2008 - 04:12

Most likely the circuit is faulty. Check show interface for errors and if any packet is being received.


Just check out whether what is CRC and reilability shown on the interface once its up and running. if its less than 255 and there are CRC then we need to assume that it could be PPP link issue. Also just the vakues shown for DCD, DTS when link goes down. Also, check whether console is giving any error forr WIC-1?



Giuseppe Larosa Sun, 06/29/2008 - 03:39

Hello Amir,

you have to check the status of the serial interface with show interface serial.

you should see all the signals up (CD, CTS, etc.)

Most probably you are not receiving the keepalive frames from remote end.

You can check this with debug serial interface.

You should see that your keepalive sequence number is incrementing but you don't see a yourseen (yourseen stucks to 0).

hope to help


mpatus Mon, 06/30/2008 - 10:11

Verify your CSU/DSU clocking is setup properly.


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