cisco native vlan

[kitus]

Hello guys, could someone please clarify some points regarding to cisco vlans and 801.Q?

Trying to merge an already existing production environment with a new management environment I had to design a cisco template for cisco catalyst where the production data is to be sent over an untagged vlan different from vlan 1 because of compatibility issues with our backbone router, an Extreme BlackDiamond router.

I've been looking for information on native vlan quite a lot this last days and to my understanding, over VLAN 1 the switch not only sends data, but information regarding PAgP, CDP, VTP over VLAN 1 by default and even if VLAN 1 is shutted down or not allowing VLAN 1 to be sent over a trunk, this protocol status information is sent anyway over VLAN 1, or something like that... To me, it doesn't make any difference to change the default native to a different vlan, does it? I mean, if there is no tagging anymore, what does it mean?

The question is, what's the point of setting up one trunk port with native vlan 200 for example? is vlan 1 still active? is this protocol information to be sent over vlan 200 or over vlan 1? Why are there some documents pointing out not to use vlan 1 for management purposes when some of them suggest that vlan 1 should be used for management proposes? have I messed it all up?

I hope that in spite of my english, i made myself clear enough.

Thank you very much in advance,

marc

 

[MTandSAV]

I think you're pretty much correct in what you're saying. Vlan 1 is indeed use to CDP info etc even when you are not using it. You can't delete vlan 1 either.

Best practise is not to use vlan 1 at all because its already used for other things.

CCNA, CCNP..partly

 

[kitus]

Thanks a lot MTandSAV,

but what's the point of having the possibility of setting a vlan different from vlan 1 as native? i really don't get it... The communication is untagged and so on... but, what's the point of it? if I sniff the communication, how do I know where are the packets comming from? If I set vlan 200 as native, is this protocol stuff sent over vlan 200 or 1? is there actually a difference or it is just a useless thing?? any CCIE out there?

 

[kitus]

Hello??? Could somebody please throw some light on this?

thank you very much

Marc

 

[KiscoKid]

Ok the management VLAN is simply the VLAN that allows you to manage your switch. All Cisco Layer 2 switches allow you to allocate an IP address for management on a VLAN of your choice. The default management VLAN is VLAN1 however this can be changed to anything you want.

Changing the management VLAN does not affect stuff like PAGP or VTP. They will continue to use VLAN1.

A native VLAN is only really relevant to a trunk port. Any traffic sourced from the native VLAN does not get tagged on a trunk port. All non-native VLAN traffic is tagged however with a dot1q header that resides in the IP type/length header field.

I think that's it in a nutshell.

 

[chieftan]

What is being said is that if you have an 802.1q trunked port then the Packet is tagged on Egress normally (exiting the port). This is because a trunked port is designed to allow more than 1 vlan across its link. It has to know which vlan it is designated for at the far end.

It is important to note that when setting up an 802.1q trunk BOTH ends of the link configuration must be identical.

 

[msalomon]

Why not mention the fact that VLAN 1 is switched in the software whereas other VLAN's uses faster hardware switching (according to my Cisco instructor on ICND).