Tagged Frames on the Native VLAN

nezzy456

Hi Guys,

I have just read this section from the CCNA 4.0

Some devices that support trunking tag native VLAN traffic as a default behavior. Control traffic sent on the native VLAN should be untagged.

If an 802.1Q trunk port receives a tagged frame on the native VLAN, it drops the frame. Consequently, when configuring a switch port on a Cisco switch, you need to identify these devices and configure them so that they do not send tagged frames on the native VLAN. Devices from other vendors that support tagged frames on the native VLAN include IP phones, servers, routers, and non-Cisco switches.

Now I thought the Native VLAN was used for trunking e.g Sending VLAN 10,20, and 30.

So why would you want to untag the frames as this is will remove the benifits of using a VLAN?

Or have I misunderstood and are Native VLAN's a VLAN put aside for solely untagged traffic?
If that is the case which VLAN(s) are used to traverse the network?

Cheers

Stotic

Native vlans are for untagged traffic.

Any vlan created can be used to traverse a network as long as trunking is configured on links between switches. You can filter the vlans that are allowed to traverse trunks. Please note that from a design perspective, a particular vlan should not leave the distribution layer as you want to localize vlan traffic as much as possible.

nezzy456

Thanks Stoic,

I have just been playing with packet tracer and I think it has become a lot clearer.

Basically like you said I would set up the trunk to take all the VLAN's e.g 10,20 and 30 and then a Native VLAN of 99 on the same port which will enable untagged traffic to traverse the connection as well as tagged traffic.

Stotic

Yes, but make sure the native vlan is identical on both ends of a trunk otherwise you will get "Native VLAN Mismatch" error messages.

rwwest7

Isn't the native VLAN always VLAN 1 by default?

Highspade

rwwest7 wrote: »

Isn't the native VLAN always VLAN 1 by default?

Yes, but like most things it can be changed.

phoeneous

Stotic wrote: »

Yes, but make sure the native vlan is identical on both ends of a trunk otherwise you will get "Native VLAN Mismatch" error messages.

Or as Jeremy Cioara calls it "VLAN Seepage". Doesnt that sound like a venerial diesease?

nitish0589

hi all,

Native vlan: when any device connected in the sw network and that device is not a member of any vlan and when that device sends a data across the trunk then that traffic can be received on the native vlan.

By default we vlan1 as native vlan and we can redefine it into any of the normal vlan or even any operational vlan can be act as native vlan but the actual catch is that always assign same vlan as native on both side of trunk other wise switch always flags a log with description NATIVE VLAN MISMATCH.