Purpose of Native VLAN

[Muhammad Haseeb]

Is there any other purpose of Native VLAN other than creating Trunk Ports. Can trunk ports be configured without Native VLAN. ? Please HELP ......

[sarahr202]

Wireshark and with SPAN on the switch

[JeyaMohanMurugesan]

By Milan ==

"CDP, VTP, and PAgP updates are always forwarded on trunks with a VLAN 1 tag."

So CDP, PAgP and VTP frames would be sent with the VLAN1 tag on the trunk between the switches in your example, wouldn't they?

So CDP,PAgp and VTP frames would be sent with thte VLAN1 tag on the trunk between the switches, what will happen if we admin down VLAN1. In our office we don't use VLAN1.

Could you please explain me about Native VLAN concept, since we admin down the default VLAN whenever adding a New access switch into production.

My current setup is cisco Two tier architecture. Core-access layer)

[milan.kulik]

Hi,

the document I was referring to

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/24330-185.html#cg18

is saying:

" You can limit the VLAN 1 transmission of user data and operation of STP on an interface. Simply do not configure the VLAN on the trunk interface.This configuration does not stop the transmission of control packets from switch to switch in VLAN 1, as with a network analyzer. But no data are forwarded, and STP is not run over this link."

In other words:

If you disable VLAN1 on a trunk, the user data and STP traffic is disabled only within it.

But not the control protocols like CDP, PAgP and VTP.

I have not captured frames to confirm, it's just what Cisco document says.

Best regards,

Milan

[JeyaMohanMurugesan]

And please let me know, is there any necessary to allow VLAN 1 on trunk. If not what will happen? Will that untagged traffic move on trunk link?

[milan.kulik]

Hi,

my understanding of the document is:

If you disable VLAN1 on  a trunk, user data and STP frames will not be sent through it. But the control protocols like CDP, VTP and PaGP will still be sent in VLAN1 on the trunk. Untagged if VLAN1 is left as the native VLAN or tagged if you configure a different VLAN as native.

BR,

Milan