Protocol link status is up/down repeatly

[junejun92]

Protocol link status is up and down repeatly.

What is usual problem and solution?

Plz help me. 

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[Leo Laohoo]

Post the complete output to the command "sh interface Serial1/0".

[Leo Laohoo]

What is the model of this router?

[MHM Cisco World]

LCP is stopped 

There is mismtach between your router and ISP'

Did you config any auth? PAP or ChAP?

Share interface config let me check it

MHM

[liviu.gheorghe]

Hello @junejun92 ,

is this serial 1/0 connected to a leased line provided by a telco? In this case you should get in touch with them, raise a ticket and ask them to investigate.