Untagged

[husamabobakr]

Dears,

i have one question regarding native vlan.

i have two switch as below :

SW1

inter f0/1

swicht port mode trunk

switch port trunk allow vlan 5-20

switch port trunk native vlan 10

SW2

inter f0/1

swicht port mode trunk

switch port trunk allow vlan 5-20

switch port trunk native vlan 100

the queistion is how sw2 will handle the traffic coming from sw1.

per to my understanding the traffic will be drop due to mismatch on the native vlan.

[Jon Marshall · Accepted solution]

If STP is running (and it should be) then it will see a native vlan mismatch and will put the port into blocking mode which is really what you want it to do. 

If STP is not running then you have in effect joined two vlans together which is not really what you want to do. 

Jon

[Joseph W. Doherty · Accepted solution]

If CDP is enabled, it will complain too, but as Jon notes, it's possible to "join" to different VLANs.

Similar can be accomplished if you join to "access" ports defined in different VLANs.

[husamabobakr]

Thanks Mr, Joseph W.

[husamabobakr]

Thanks Mr, Jon Marshall

[Dan Lukes · Accepted solution]

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the queistion is how sw2 will handle the traffic coming from sw1.

VLAN10  packets are sent untagged by SW1. SW2 considers untagged packets to be VLAN100

per to my understanding the traffic will be drop due to mismatch on the native vlan.

With no CDP enabled, switch knows nothing about it. Even with CDP enabled, it's just warning. Packets are still processed according configuration. But STP may block them.

See also Native VLAN mismatch and CDP

[husamabobakr]

Thanks a lot Mr,Dan Lukes :)