trunk formation

Answered Question
Nov 21st, 2008
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hi every body!

Can the trunk be brought up using

dtp between two switches ,each having different native vlan provided that encapsulation is manually set to dot1q?

I understand that even if the trunk does come up, two native vlans on switches won't be able to communicate.But i just want to know if the trunk does come up or not.

2) how about if we configure the different native vlans on each switch, configure the trunking manually i.e encapsulation set dot1q and port mode is set to trunk, will the trunk come up?

thanks a lot!

Correct Answer by Jon Marshall about 8 years 6 months ago

Sarah


The trunk will come up but you should see %CDP-4-NVLANMISMATCH error messages in your logs and traffic for the native vlan will not be transmitted correctly.


Jon

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John Blakley Fri, 11/21/2008 - 13:15
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Trunks should form I would think (although never tried). While you're configuring manually though, why don't you just set your native vlan?


--John

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Jon Marshall Fri, 11/21/2008 - 13:17
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Sarah


The trunk will come up but you should see %CDP-4-NVLANMISMATCH error messages in your logs and traffic for the native vlan will not be transmitted correctly.


Jon

glen.grant Sat, 11/22/2008 - 03:04
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If you have different native (untagged vlans on each you run the risk of bridging those 2 vlans together and causing problems . If you hardcode the trunk to on then if you have a layer 1 link it is going to show trunking even if the trunk is not working correctly hence the problem with forcing on the trunks , which is why both sides should be exactly the same no matter which trunking method is used. A little blurb from a cisco doc.


•When connecting Cisco switches through an 802.1Q trunk, make sure that the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning tree loops can result.

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