Line protocol is down

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May 3rd, 2007
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Hi. Two of my company's routers, are connected with 2 serial connection with each other. No multi link interfaces are defined. Serial 0 works fine, but Serial 1, after issuing "no shut" command, works couple of seconds, and change it's state to "Serial1 is up, line protocol is down". Both routers running EIGRP. Is this problem is L1 issue, or maybe EIGRP protocol have something with blocking interfaces to prevent some kind of loop? Second part of problem is that branch office router, configured with EIGRP and same AS number as rest of routers, does not have any routes learned dynamically... To one who is interested to help, I can send short config output for EIGRP, ACL, etc.



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Overall Rating: 4 (4 ratings)
cfabeny Thu, 05/03/2007 - 08:18
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Hello Igor,

Line protocol down simply means that the L2 protocol (cisco hdlc by default) cannot communicate for some reason. You'll want to verify the configuration on both sides of the link first. Then investigate the transmission path. This is not related to EIGRP or layer 3 issue.

guruprasadr Thu, 05/03/2007 - 23:07
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2 - Routers connected via Serial Ports.

One end should be a DCE & other end is DTE.

Can you Check whether you applied the "Clockrate as 64000" to the DCE interface.

Pls Rate if Helps ! !

Best Regards,

Guru Prasad R

haroon.shaikh Fri, 05/04/2007 - 00:25
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Check clockrate as in the previous post.

Also check if your encapsulation protocol is same on both ends (i.e. PPP or HDLC on both ends). If you use different encapsulation protocols, the line protocol will be displayed as down after couple of seconds.

Also, if you are using PPP as encapsulation protocol and if you have configured authentication, you need to make sure you are using correct authentication strings on both ends. Hope that helps....

* Please rate if it helps

machiavelli Fri, 05/04/2007 - 01:50
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Thank you all for the fast responses. Problem was in the line itself, and after line fixup by Telco, traffic across that link was established.

Thank you, again.



mohammedmahmoud Fri, 05/04/2007 - 00:34
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Can you please past the interface configuration and the show interface, it is not a routing problem.


Mohammed Mahmoud.


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