Serial Interface keeps going up and down

[bryan.crouch]

I have a serial interface that goes up and then back down about every 30 seconds. Does anyone know of any debug commands that I can put on this sub interface to determine what could be causing this. I have 14 other remote locations workling fine. I am positive all of the cabling is good. Just kind of at a loss. I looked at the interface and there are packets barely going in and out and they all have errors. thanks in advance for any help!!!!

By the way, it is a 1751

[rjackson]

The high error rate is not letting keepalives through so the circuit is probably never really coming up. It tries to periodically and those attempts are logged as up / down cycles. Look in the sh int for a high and incrementing interface reset count. That means the router is reseting the circuit because of the keep alive failures. In my experience its usually a carrier problem.

[ubiifereo]

This solved my flapping serial interface issue.

[mmasha]

HI

you can write this command on your serial interface .and solve your problem.

NO KEEPALIVE

but you should check other side router , if in the other side is non-cisco router set your encapsulation on the both serial interface to PPP and if your interface is a transmit only , you should set IGNORE-DCD on the interface that only received .

Hope to do help.

NIX TECH.

Mohsen.

[deilert]

I would not recommend doing the ignore dcd or tunring off keep alives , you will neverf know if you have a problem with these commands , it is putting a band aid on the problem instead of correcting the root cause that is most likely a problem with your carrier .

Can you paste in a sh interface for this interface