1.5 Native VLAN (question not asked yet)

Hello community,

The requirement in task 1.5 is the following:
"Modify the native VLAN on the 802.1q trunks of SW1 so that traffic between devices in VLAN 146 is not tagged when sent over the trunk links."

The solution guide says:
SW1:
interface range FastEthernet0/13 - 21
switchport trunk native vlan 146
SW2:
interface range FastEthernet0/13 - 15
switchport trunk native vlan 146
SW3:
interface range FastEthernet0/13 - 15
switchport trunk native vlan 146
SW4:
interface range FastEthernet0/13 - 15
switchport trunk native vlan 146

The problem I have with the answer given in the solution guide is the fact that the native VLAN was changed in all switches. The task says "modify the native VLAN on the 802.1q trunks of SW1" so I first thought, OK this means all ports on SW1 and ports 13-15 of all switches (as given in the solution guide) but then I read the second statement of the task that says "so that traffic between devices in VLAN 146 is not tagged when sent over the trunk links." With this second statement then I changed my thoughts and understood that only switches that have nodes in VLAN 146 or are in transit for VLAN 146 need to have their trunks with native VLAN 146. So my solution was the below configuration because SW3 does not have VLAN 146 at all:

sW1
int ra f0/13-15 , f0/19-21
 sw t native v 146
SW2
int ra f0/13-15
 sw t native v 146
SW4
int ra f0/13-15
 sw t native v 146

I understand the configured native VLAN does not need to exist in the switch, such as the case of SW3, but the statement in the task clearly says "so that traffic between devices in VLAN 146 is not tagged when sent over the trunk links" so if SW3 does not have VLAN 146 configured how will traffic ever travel through its trunk to SW1?

What is your opinion about my thoughts on this task VS the solution given in the guide please? Maybe I am misunderstanding the question so I'd like to hear from others.

Thanks in advance

Comments

  • STP root bridge and/or physical topology change could force traffic through SW3 for vlan146, but I didn't research the specifics of this particular lab and topology. I am merely giving a possible scenario that would force traffic across SW3 even though, as you say, nothing hangs out of it for that vlan.

  • JoeMJoeM ✭✭✭

    I understand the configured native VLAN does not need to exist in the switch, such as the case of SW3, but the statement in the task clearly says "so that traffic between devices in VLAN 146 is not tagged when sent over the trunk links" so if SW3 does not have VLAN 146 configured how will traffic ever travel through its trunk to SW1?

    What is your opinion about my thoughts on this task VS the solution given in the guide please? Maybe I am misunderstanding the question so I'd like to hear from others.

    Hi Gabe,

    If we change the native vlan on all trunks for SW1,  the other side must be changed also.

    It looks like you have a good understanding of your L2 map/vlans. This is good, but do not read too much into this particular task.  As long as the three devices in Vlan146 (R1,R4,R6) can communicate.  This is not a full lab, just a short warm-up task about changing the native vlan.

    In bigger labs, I think that if there is traffic not being forwarded over certain switches, we would just add the needed vlan where needed.

  • Thank you guys for replying :)

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