Access port connected to a trunk port

[ramez.dous]

SW0 "F0/0" <---> SW1 "F0/0"
Access port "VLAN10" <---> Trunk port
Will SW0 drop all frames coming from SW1 or it will process packets from the Native VLAN?
What if SW1 Native VLAN is VLAN 10?

[Karsten Iwen]

It's typically a misconfiguration but it will work as you assume. Whatever SW1 sends in it's native VLAN, SW0 will take that as VLAN10 traffic. And if SW1 has VLAN 20 as native VLAN, the traffic just "hopped" from VLAN 20 to VLAN10.

[calebmo12]

Hi,

The native vlan is only for untagged packets, so any packets incoming that has no tag attached to it on a layer 2 basis will be caught by the native vlan tag, in your scenario, if the layer 2 VLAN 10 is defined on both ends and allowed across the trunk port on Sw1, it will not dropped however any other vlan traffic will be dropped. because SW0 is defined as an access port.

Hope this helps you.

[nixpengu1n]

Hello,

By default packets will be processed, so clients in VLAN 10 on both switches will remain connectivity. However depending on Fa0/0 ports configuration on both ends, this "access-trunk" link may not be formed at all and / or might be blocked. 

However this connection approach is not correct and may lead to serious LAN connection problems.

[ramez.dous · Accepted solution]

Thank you guys.
I did a test and it "worked" the way I expected.

PC0 <---> SW1 F0/2 "Access VLAN10"
SW1 F0/1 "Access VLAN10" <---> SW2 F0/1 "Trunk"
SW2 F0/2 "Access VLAN1"Native"" <---> PC1
PC0: 192.168.1.1/24
PC1: 192.168.1.2/24

PC1 was able to ping PC0
PC1 was able to ping SW1 native VLAN "VLAN1" interface "192.168.1.101"
PC0 was able to ping PC1
PC0 was able to ping SW1 native VLAN "VLAN1" interface "192.168.1.101"

[huynhnam]

it will tell that native vlan mismatch on 2 switch, right ?