Line Protocol Down

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Mar 10th, 2008
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hi all, we have a leased line and out interface S0/1 is showing up line down. We've spoken with BT who say leased line is fine.The other end of the serial cable is connected to a box and the next hop address for our routes cant be reached now. what is the best way to troubleshoot leased line issues? thanks



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sham_chennala Mon, 03/10/2008 - 05:15
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Hi,

You just check the encapsulation of your line it may be because of that.

Regards,

Sham


solpandor Mon, 03/10/2008 - 05:16
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sham, the encapsulation is HDLC and it was working fine this morning and just suddenly stopped. there have been no changes made to our router



sham_chennala Mon, 03/10/2008 - 05:40
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Hi, can you reset it. first you shut down your interface by using shutdown.

and shutdown the ip and all then try to re configure it.It May work.

Regards,

Sham


smitty6504 Mon, 03/10/2008 - 05:15
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You need to get a loopback plug or create a loopback plug. Once that you create the loopback plug get a network cable and put the loopback plug on the end and plug that into the smartjack. If all the lights go green then the circuit is fine and you have a router config issue or a WIC issue else it's a circuit issue.

solpandor Mon, 03/10/2008 - 05:27
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smitty

thanks for reply but i dont think i follow the rest of your post.

Once i create the loopback what do i do with it?

smitty6504 Mon, 03/10/2008 - 05:33
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Once it is created you will need to plug it into the WIC with the router on. This should bring the interface up. Try that first. If that works then take the loopback cable to your phone room and plug it into your smartjack. This will cause the circuit to come up and the alarm on the smartjack should go out after a few minutes. If it doesn't it would be circuit issue.

Richard Burts Mon, 03/10/2008 - 05:27
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Suleiman


When a serial interface shows line protocol is down it is caused because of a failure of keepalives on the interface. Assuming that there is not a problem on the circuit, my experience is that these kind of things will cause line protocol down. I suggest that you check for these:

- mismatched protocol - if one end is HDLC and the other is configured for PPP or something else then keepalives will fail. You need to check the devices on both ends. And do not let it be on the basis of what someone remembers it was configured for - have someone check the running-config now.

- one end configured for no keepalive and the other end configured for keepalive. This will cause the end configured for keepalive to be protocol down.

- I have seen situations where one end was configured with a different keepalive timer and it caused at least intermittent line protocol down.

- problems with clocking on the circuit. If one or both ends are experiencing problems with clocking on the circuit it can cause line protocol down.


I realize that one of your posts says that the router did not change. But if the connection was working and is now not working then something must have changed. I suggest that someone check both ends again and verify that the configurations match.


HTH


Rick

solpandor Mon, 03/10/2008 - 05:31
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rick, the other end is just a box, and i dont know how to get into to it to check keepalive or encapsulation. on our router the encaps is HDLC and keepalive are set to 10sec. when i shut the interface down and bring it back up, its ok for approx 15 secs then goes down again..how would i check the encaps and the keepalive on the other box?? would the service provider be able to check that?



solpandor Mon, 03/10/2008 - 05:33
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also, ive cleared the counters and its sending packets but not receivng any...


Richard Burts Mon, 03/10/2008 - 05:45
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Suleiman


If you shut and no shut the interface it will start with line protocol up and will attempt to transmit (at least to transmit keepalive packets and perhaps other things as well). When the keepalives fail - because it is receiving no packets keepalives - then the line protocol goes down.


If you have checked your end and find no problem then the issue may be on the other end. What kind of box is this that you connect to? Who owns that box and who maintains it? If it is a service provider box then they should be able to check it. If it is not a service provider box then I doubt that the service provider can do much to tell what it is doing.


HTH


Rick

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