Error on Native VLAN with 3 switches

[VitDoc]

Hi! I was studying VLANs and testing some native VLAN projects on Packet Tracer 6. 

I've built this network with 2 segments, each one using a different native VLAN for both ports to avoid mismatch. In my project, SW1-SW2 segment is configured with VLAN10 as native and SW2-SW3 using VLAN1 as native. The problem I'm facing is VLAN 1 frames correctly cross the native 1 VLAN segment using IEEE802.1Q tag but then keep using it even on native VLAN 1 segment. The same occurs for VLAN 10 frames on SW2-SW1 path. Do you have any ideas of what maybe's happening?

SW1#sh int tru

Port Mode Encapsulation Status Native vlan

Fa0/3 on 802.1q trunking 10

Port Vlans allowed on trunk

Fa0/3 1-1005

Port Vlans allowed and active in management domain

Fa0/3 1,10

Port Vlans in spanning tree forwarding state and not pruned

Fa0/3 1,10

---------------------------------------

SW2#sh int tru

Port Mode Encapsulation Status Native vlan

Fa0/1 on 802.1q trunking 10

Fa0/2 on 802.1q trunking 1

Port Vlans allowed on trunk

Fa0/1 1-1005

Fa0/2 1-1005

Port Vlans allowed and active in management domain

Fa0/1 1,10

Fa0/2 1,10

Port Vlans in spanning tree forwarding state and not pruned

Fa0/1 1,10

Fa0/2 1,10

---------------------------------------

SW3#sh int tru

Port Mode Encapsulation Status Native vlan

Fa0/1 on 802.1q trunking 1

Port Vlans allowed on trunk

Fa0/1 1-1005

Port Vlans allowed and active in management domain

Fa0/1 1,10

Port Vlans in spanning tree forwarding state and not pruned

Fa0/1 1,10

[luis_cordova]

Hi @VitDoc ,

The purpose of the native vlan is to assign a vlan number(tag) to the packets that arrive at the switch without a tag.

In the case that you have configured a switch port to assign a specific vlan, the packets that arrive at it will be tagged with that vlan number.

Switch(config-if)#switchport access vlan n°

If a packet without a tag arrives at the switch (for example, from a non-manageable switch), it will be tagged with the number of the native vlan.

Now, if a packet has already received a tag from the native vlan, at the input port, this tag will remain associated with this packet and hops to the next switch with the tag already adopted.
Therefore, it would not adopt the tag of the native vlan configured in the output port nor the tag of the native vlan of the next switch.

Regards

[Martin L]

can u share PT file here or use Sim mode of PT to figure things out