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New Member

serial 0/1 is up, line protocol is down (looped)??

Does anyone know what exactly would cause a T1 serial interface (point to point T1) to be up but with line protocol down (looped)? I am not showing any CSU/DSU errors or loopbacks but the interface is showing this loopback. I seached CCO and have seen plenty of references to line protocol being up (looped) but no line protocol down (looped). I have a ticket open with the telco now to see if they are screwing anything up but am not sure they are. Any thoughts? I have also tried a differant CSU/DSU and serial port with the same symptoms.

5 REPLIES
Silver

Re: serial 0/1 is up, line protocol is down (looped)??

I've come across the same situation a lot of times also, but never found anything in CCO that was specific to it.

Analysing it, an interface reports loops when it detects its own messages returning to it. Line protocol comes up when it recieves keepalives from the interface. The situation could therefore be due to a slightly noisy line.

I would like to know your findings. Please keep us posted.

New Member

Re: serial 0/1 is up, line protocol is down (looped)??

As soon as the carrier ran a loopback to the smartjack at the remote site and then removed it the circuit came back up. All I know is the problem is fixed and the telco took way too long to fix it.

Re: serial 0/1 is up, line protocol is down (looped)??

Hi

do chek whether u hve down-when-looped issued under that particular interface and also whts the encapsulation type being used in tht interface.

regds

prem

New Member

Re: serial 0/1 is up, line protocol is down (looped)??

It is PPP encapsulation, and I have no loopbacks set on the interface. If I pull the T1 cable though the interface goes down, down with no loop.

Re: serial 0/1 is up, line protocol is down (looped)??

hi

its the encapsulation due to which you are getting protocol down(looped),that is you are getting loop from u r telco side.

if u want to confirm the same ,just change the encap to hdlc when gettin the status as down(looped) u will get serial up protocol up(looped).

Get in touch with u r local telco and get it sorted. but make sure tht u r reverting bck to ppp after cheking the same.

regds

prem

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