Router Down/UP

[bob.mckinley]

I was recently asked this question in an interview, and since I haven't worked with routers in some time I couldn't really answer completely so for future references I was hoping some one could help me with a correct answer.  This is all the question had to it, I'm sure I could have followed asking for more details, but I think they were looking for more general answer, and I didn't want to look even worse by getting more confused with more details.  Any help would be greatly appreciated.

On a Cisco router, is it possible to have an interface show DOWN/UP? If so, when?

Thanks,

Bob

[Gregory Snipes]

Are you sure they did not mean UP/DOWN? There are two different status to a router interface one is the status of the physical interface the other is the status of the line protocol. The status is typically expressed with the physical status first and the line protocol status second. There are many different scenarios where an interface may be UP/DOWN but (and correct me if I am wrong all) I cannot think of any circumstance in with the line protocol would be up and the physical interface is down.

[bob.mckinley]

That's kind of what I thought too, they meant UP/Down, however the question read Down/Up I thought it was odd too, only thing I could think of is that they left administratively part off the Down section to throw me off, but I find it hard to believe that it wouldn't ever be possible to see that, kind of like a trick question I think..

Thanks,

Bob

[SCCisco22]

I would agree with Gregory. So the answer to your question would be, no it not possible to have an interface show DOWN/UP. Layer 1 must be up for layer 2 to be up.


Sent from Cisco Technical Support Android App

[ALIAOF_]

Sounds like a trick question, at times interviewing people will do that they will ask you a question and expect you to correct it.  I guess they want to see if you really know it.

[Leo Laohoo · Accepted solution]

Down/Up?

That's a trick question.  Not possible because that would mean your Layer 1 is DOWN but your Layer 2 is UP?  Not possible.

Oh wait ... BER/Loop test.  Now that's possible on a non-Ethernet link like FR or IMA ATM, etc.. 

[bob.mckinley]

Leolaohoo, is correct.  On a Loop test it's possible to have the interface read Down/Up.  I reached out to the interviewer to get more information on that question.  He said a Loop test, can cause the interface to show that, it will actually show some other weird results too, but that's how it's possible.

Thanks everyone for their feeback, I appriciate the help!

Bob

[Leo Laohoo]

Thanks Bob.

I have not seen loop/BER test for a loooong time.  So I'm not sure if you can do a test like this on an Ethernet connection.  The interviewer's gotta be an old hand back from the Frame Relay/X25 days.