down and administratively down

Unanswered Question
Aug 28th, 2004
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If you see that an interface is down, there is a problem with the physical layer. If you see it's an administratively down, that means the cable is ok but the interface has been shut down manually or by default. Could it be also a cause that the cable is unplug for the second case?

A protocol down means the datalink layer has problem or both the network and datalink layers?

any one please kindly help clerify that. Thanks.

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Overall Rating: 5 (1 ratings)
Loading. Sun, 08/29/2004 - 09:02
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For Ethernet Interfaces:

If the routers interface is administratively up (no shut) and there is no cable plugged in, you will see "interface is up, line protocol is down"

Also, if you have a cable plugged into the device, but the device you are connecting to is down, you will see "interface is up, line protocol is down"

I believe its different for Serial interfaces where as if you unplug the cable, you can cause a down/down siutation

If im not mistaken, the first "down" indicates a physical problem (layer 1). The line protocol down indicates a layer 2 issue (not receiving keepalives).

You can cause an up/up situation with ethernet by using a no keepalives option. But it wont "really" be up.

Someone please correct me if Im wrong I really havent looked at details of this in a while...


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