The network administrator is trying to add Switch1 to the network, but the 802.1Q trunk is not coming up. Switch1 was previously tested in the laboratory and its trunk configuration worked fine. What are three possible causes of this problem? (Choose three.)
A.
The trunking configuration mode on Switch1 is set to Off.
B.
The trunking configuration mode on the other end is set to On.
C.
The trunking configuration mode on the other end is set to Desirable.
D.
Cisco Discovery Protocol is not running on the other end.
E.
There is a VTP domain name mismatch.
F.
Switch1 does not support 802.1Q.
Explanation:
There are 5 possible trunking modes for a switch port:* Auto: this is the default mode. In this mode, a port will become a trunk port if the device the port is connected to is set to the on or desirable mode.
* Desirable: allows the port to become a trunk port if the device the port is connected to is set to the on, desirable, or auto mode
* On: sets the port to permanent trunking mode.
* Nonegotiate: sets the port to permanent trunking mode without sending Dynamic Trunking Protocol (DTP) frames
* Off: sets the port to permanent non-trunking modeIn this case, we can guess the trunking mode of Switch 1 is auto (default mode). When in the laboratory, the trunking mode of the other end is set to On or Desirable
so 2 switches can negotiate and the link becomes trunk with no problem. But when plugging to the network, other switches may have the trunking mode set to auto so
the 802.1Q trunk is not coming up -> B C are correct.Of course these switches need to be in the same VTP domain so that they can talk with each other -> E is correct.
I disagree with BCE answer.
E – seems to be correct – different VTP domains cause trunk negotiation problems.
F – is true – we may have used ISL trunk in the lab, but 802.1q is unsupported on our switch and ISL is unsupported on the other end.
D – is wrong – CDP is not required by a trunk, moreover in case of VTP domain mismatch it would help
C – desirable state will not bring up a trunk only if the other end is in access mode or has switched off negotiation. So the answer would be right if we had trunk+nonegoitiate in the lab.
B – is wrong as on mode will not work only with access mode, but then we would have a failure in the lab as well.
A – is ridiculous, but correct in this case my opinion. It is unclear if it means access port or nonegotiate port, but in both cases we may run into trouble.
So I would say AEF.
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