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I have 2 switches running on 802.1Q trunking mode. On both switches the default vlan is 1.

  1. If I were to configure the native vlan to 2, can vlan 1 traffic still travel from switch to switch?
  2. After I configure the native vlan, do i need to allow it in the trunk? like switchport trunk allowed vlan 2?
  3. Does that means all untagged traffic like vlan 1 connected pc's will go to vlan 2 under native vlan in trunk? Do i need to configure vlan 2 access mode?
  4. Does it happen like this: In first switch, all untagged frames like vlan 1 will goes under native vlan 2 in the trunk. Then they will travel across the trunk. After reach switch 2, these untagged frame belongs to vlan 2. These frame can talk to those untagged vlan 2 (vlan 2 access port). Am i right?
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    You will need a layer 3 interface for each vlan if you want them to be able to communicate to each other.Assuming each vlan is a seperate subnet.
    – NineTail
    Nov 8, 2017 at 19:15
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin ♦
    Feb 19, 2018 at 20:04

2 Answers 2

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If I were to configure the native vlan to 2, can vlan 1 traffic still travel from switch to switch?

Yes, now VLAN 1 is tagged. VLAN 2 is untagged.

After I configure the native vlan, do i need to allow it in the trunk? like switchport trunk allowed vlan 2?

By default, all VLANs are allowed on the trunk. If it was allowed before, it still is.

Does that means all untagged traffic like vlan 1 connected pc's will go to vlan 2 under native vlan in trunk? Do i need to configure vlan 2 access mode?

VLAN 1 is now tagged on the trunk port. The access ports work the same.

Does it happen like this: In first switch, all untagged frames like vlan 1 will goes under native vlan 2 in the trunk. Then they will travel across the trunk. After reach switch 2, these untagged frame belongs to vlan 2. These frame can talk to those untagged vlan 2 (vlan 2 access port). Am i right?

No, you're a little confused here. Frames are only tagged on trunk ports. Since you have set the native VLAN to 2, all other VLANs will be tagged. VLAN 1 is still VLAN 1, whether it's tagged or not.

I think you're confused by the term 'default.' All that means is that VLAN 1 exists on the switch(es) without you having to explicitly create it.

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I think Ron answered the first 3 questions in a great way,

Just to illustrate on the last question.

suppose you have switch A with native vlan 1 and switch B with native vlan 2.

this means that traffic that originated from the VLAN 1 on switch A will be understood as VLAN 2 traffic on switch B. this means that - as far as layer 2 is conserned - clients on VLAN 1 on switch A and clients on VLAN 2 on switch B are on the same broadcast domain.

this however means that traffic that originate from VLAN 2 on switch A will be discarded on switch B because VLAN 2 traffic should not be tagged. and vise versa.

it is most likely that the switch will show you an error if this happens, also it's a good practice to tag all VLANS.

Hope this helps

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