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Troubleshoot serial interface

I have serial HDLC connection between 3640 and 1720 with 2 sdsl modems. I have line up and protocol down.

I have regular eigrp configured fine (i tested with 2 1720 and same modems)

When I turn on debuging on serial i get message

Serial0: HDLC myseq 114, mineseen 0,yourseen 0, line down

Serial0: HDLC myseq 115, mineseen 0,yourseen 0, line down

Serial0: HDLC myseq 116, mineseen 0,yourseen 0, line down

..........

What could be a problem?

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Re: Troubleshoot serial interface

According to these debug results this interface sends regular HDLC keepalives but sees nothing coming from the other end. If you're sure about configs, probably a layer-1 connectivity problem. You can first check cable/connector/modem issues and transmission path with telco.

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