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VTP and vlan 1.

I wonder if VTP updates are forwarded on 802.1Q trunks tagged even if vlan 1 is the native vlan of the trunk.

In the document

"Best Practices for Catalyst 4500/4000, 5500/5000, and 6500/6000 Series Switches Running CatOS Configuration and Management"

you can read:

"CDP, VTP, and PAgP

updates are always forwarded on trunks with a VLAN 1 tag."

As the document does not say if the vlan 1 is or not the native vlan, it seems that the statement is valid also when vlan 1 is the native vlan of the trunk.

What do you think about?

5 REPLIES

Re: VTP and vlan 1.

Hello!

As I remember, the Cisco documentation always assume that on Cisco devices, Vlan 1 is the native one.

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_configuration_example09186a008009478e.shtml

"If you do not explicitly define a native VLAN,  VLAN 1 becomes the       native VLAN by default"

Cheers,

Calin

Hall of Fame Super Blue

Re: VTP and vlan 1.

speculor_cisco wrote:

I wonder if VTP updates are forwarded on 802.1Q trunks tagged even if vlan 1 is the native vlan of the trunk.

In the document

"Best Practices for Catalyst 4500/4000, 5500/5000, and 6500/6000 Series Switches Running CatOS Configuration and Management"

you can read:

"CDP, VTP, and PAgP

updates are always forwarded on trunks with a VLAN 1 tag."

As the document does not say if the vlan 1 is or not the native vlan, it seems that the statement is valid also when vlan 1 is the native vlan of the trunk.

What do you think about?

As Calin said, vlan 1 is the native vlan by default. So control traffic such CDP/VTP/PAgP will be not be tagged. If you change the native vlan to something other than vlan 1 then the control traffic will be have to have a vlan 1 tag added to the frame.

Note that it is recommended best practice to change the native vlan from vlan 1 to a vlan that has not ports in it and does not have a L3 SVI for it.

Jon

New Member

Re: VTP and vlan 1.

Hello Jon.

But the statement does not say that, if the native vlan is vlan 1, the frame is untagged, and that, if the native vlan is not vlan 1,

the frame is tagged.

The statement says that "VTP updates are always forwarded on trunks with a VLAN 1 tag".

The statement does not make difference between the two cases.

Have you ever seen those frames with a network analyzer?

May be they are always tagged, even if the native vlan is vlan 1.

I do not think it is so important, but I wonder if the Cisco document must be interpreted literally.

Hall of Fame Super Blue

Re: VTP and vlan 1.

speculor_cisco wrote:

Hello Jon.

But the statement does not say that, if the native vlan is vlan 1, the frame is untagged, and that, if the native vlan is not vlan 1,

the frame is tagged.

The statement says that "VTP updates are always forwarded on trunks with a VLAN 1 tag".

The statement does not make difference between the two cases.

Have you ever seen those frames with a network analyzer?

May be they are always tagged, even if the native vlan is vlan 1.

I do not think it is so important, but I wonder if the Cisco document must be interpreted literally.

No i haven't done it but thnkfully this helpful chap has -

Native vlan packet captures

Now it is for a 3550 and you are referring to a document on 4500/6500 but i don't think that makes any difference to be honest.

Jon

New Member

Re: VTP and vlan 1.

Jon, thanks.

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