is up, line protocol is down

Answered Question
Mar 26th, 2008
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I've got a 2801 sitting here.


When I 'sh int', both FastEth interfaces show "interface is up, line protocol is down".


The thing is, nothing is plugged into either one... Shouldn't they both be down/down due to physical issue?


Correct Answer by Richard Burts about 9 years 1 month ago

Tyler


It is a subtle difference between router code and switch code.


HTH


Rick

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kris55s Wed, 03/26/2008 - 10:27
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"interface up" means it is admined up. Do a "shutdown" command on the interface and it will show as down/down.

Richard Burts Wed, 03/26/2008 - 10:37
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Tyler


Actually for Ethernet/FastEthernet interfaces it is normal for them to show as up/down when nothing is plugged in. Is it just that it is different from what you expected, or is there some problem involved with this?


Kristen


If you do a shutdown on the interface it will show as admin down, which is not quite the same as down/down.


HTH


Rick

kris55s Wed, 03/26/2008 - 10:41
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Yep, you're right Rick. I forgot about that. :)

tylerlucas Wed, 03/26/2008 - 10:45
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Thanks for the quick replies.


With nothing plugged in, I was expecting down/down....


When will an interface show down/down (not admin down/down)???


I thought that the first up/down was the physical layer status, and the line protocol was the layer 2 status...

Richard Burts Wed, 03/26/2008 - 10:51
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Tyler


What you describe (interface up/down is the physical layer and line protocol up/down is the layer 2 status) is the case for most serial interfaces. It is not the case for Ethernet/FastEthernet interfaces. I am not sure what it would take for an Ethernet/FastEthernet to show down/down.


HTH


Rick

tylerlucas Wed, 03/26/2008 - 10:57
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Thanks for the reply.


Interesting.


Why does a switch show down/down on fastethernet interfaces when nothing is plugged in, then?

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Richard Burts Wed, 03/26/2008 - 11:34
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Tyler


It is a subtle difference between router code and switch code.


HTH


Rick

Richard Burts Wed, 03/26/2008 - 11:47
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Tyler


I am glad that my information has been helpful. Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forum more useful when people can read a question and can know that they will read responses which did resolve the question.


The forum is an excellent place to learn about Cisco networking. I encourage you to continue your participation in the forum.


HTH


Rick

Danilo Dy Wed, 03/26/2008 - 11:48
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This is interesting conversation.


On the other hand, if you disable "keepalive" in the router ethernet interface, both physical and protocol will show up/up


Regards,

Dandy

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