management vlan 1

[michal.dudzak]

Hello, iam preparing for the ccna wireless exam and this qestion gives me big concerns because of answer.

Which change can correct inband access to the WLC? (first google result)

Answer: D
Explanation:
All of the other ports in the network are using the default VLAN (VLAN 1) but port 0/1, which
connects to the WLC, is configured as a trunk, so VLAN 1 is not operational.

I have set up lab and in order co comunicate with all wlc vlans my switchport had to be configured as trunk. encapsulation on the port without any further changes should be dot1q, or em i wrong?

on switch when command show vlan brief issued interface trunk is not appearing (which is expected behavior)

(does anybody know which command gives print on the picture?)

on this picture is clearly visible that management interface is NOT in native vlan and wlc will tag frames with vlan 1, on my switch i have native configured default native vlan (vlan 1) which means no tagging on vlan 1. in my lab worked only when i set computer and management to common vlan different than 1 (for example vlan 3 both) OR set wlc management vlan to 0 (untagged)

How can be changing encapsulation correct answer? how this can make vlan 1  not operational? (vlan 1 is fully operational even i wrote command switchport trunk encapsulation dot1q and nothing changed either it did not correct anything in my lab)

[Milos Megis]

If I understand it correctly then:
WLC will tag frames with VLAN 1. Switchport on which WLC is connected is in trunk mode with native VLAN 1. So path from WLC to switch will work.

But if switch send frame to controller, then switch remove VLAN tag 1 because it is native VLAN.
But WLC need to receive frame with VLAN tag 1, and because there is no VLAN tag, then frame will be dropped.

You have 2 options:
1. change VLAN on controller to 0 = untagged
2. change native VLAN on switch port to something different than 1 with command switchport trunk native vlan xxx so then VLAN 1 will be tagged.

[michal.dudzak]

hello Milos,

connection wont work because wlc will tag frames with vlan 1 and switch with default native vlan will not be able to decide where to forward it. 

-but first option which you described are/should be correct or that is exactly what i tried in lab.

-second option which you described wont work because same reason, wlc will send tagged frame and switch with native vlan of any number wont be able to decide where to forward it. Changing native vlan number( for example to vlan20) on switch could work only when wlc vlan is set to 0 (untagged)- in that case switch will forward frame to vlan 20 (i tried this either)

Why is  correct answer  change encapsulation that is biggest mystery, and this answer is here already 2-3 years. This is confusing as hell is that  answer bad on purpose by Cisco itself? Why nobody bothered to change it over such a long period.

[Milos Megis]

Let me correct you with this:
"connection wont work because wlc will tag frames with vlan 1 and switch with default native vlan will not be able to decide where to forward it."

if you don´t use command "vlan dot1q tag native" then WLC tag frame with VLAN 1 which is native on trunk port of switch. Switch know that VLAN 1 don´t need to be tagged and remove tag. But forward frame to next device.

But opposite direction will not work, because if frame come with VLAN tag 1, switch know that this VLAN is native and remove tag. But frame arrive to controller without any tag and due to this reason the WLC will drop frame. WLC will receive only tagged frames (in this configuration).

Of course, this change nothing on fact that connection will not work.

Second option must work. Because WLC tag frame with VLAN 1 and if you have for example native vlan 20, then switch keep frame tagged.
Of course you must ensure routing and allow vlan(s) on trunk port to make this configuration working.

Regarding encapsulation, there are not many options, only DOT1q or ISL. And I am not sure but I think that ISL is not supported by WLC.

[michal.dudzak]

thank you,

if iam right trunk encapsulation dot1q is default, than changing encapsulation wont change anything. stil i dont see how D is correct answer.

[Milos Megis]

yes you are right,

dot1q encapsulation is default, and only one on lower models.

Also ISL is not probably supported by WLC, so I also don´t see how change of encapsulation can be correct answer

[michal.dudzak]

i have no idea how to pass exam with confusing answers like this, i only wish that somebody can confirm that cisco test engine will not evaluate answer as bad if i choose F

[Leo TI]

Correct answer is F,