Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

As I understand it (and that is questionable):

This pertains to Cisco equipment.

1-Switch traffic on a port, configured in access mode with a static VLAN, is tagged with a VLAN field before being sent out the trunk port?
2-Control traffic is untagged. Untagged frames are "tagged" with the PVID of the Native VLAN?
3-The purpose of trunking is to allow multiple VLAN traffic across the same link?
4-The native VLAN is for legacy or untagged LAN traffic. The purpose is to allow any untagged traffic or traffic not associated with a VLAN to use the trunk link and still communicate with the network?

Is that right?

share|improve this question
up vote 3 down vote accepted

Indeed Trunks only carry tagged frames, the purpose of a trunk is to be able to transfer data from different VLAN's. When your frame reaches the other side, the switch will look at the tag and forward it to the correct VLAN.

A native VLAN is indeed a VLAN that carries untagged frames. However if you mean by control traffic the management VLAN, it's by default on VLAN1 just like the native VLAN, however you can configure a seperate VLAN for management traffic (which is best practice). But it's indeed also untagged.

Also if a port get's a VLAN tag it doesn't know, it's automatically placed on the native VLAN.

share|improve this answer
I did mean the management VLAN when I wrote 'control', thank you. In setting the management VLAN on something other than the default VLAN, would I then also change the native VLAN to the same VID or should the native VLAN and management VLAN be separate? – Kernel Panic Mar 4 '12 at 18:39
You seperate them, there are some attacks possible when you leave them on one VLAN, but I can't recall them immediately. – Lucas Kauffman Mar 4 '12 at 18:41
Don't forget to accept the answer if it solves your question :) – Lucas Kauffman Mar 4 '12 at 18:46
I thought you could have one untagged VLAN on a trunk port? – Robin Gill Mar 4 '12 at 19:29
Yes, that's the Native VLAN – Lucas Kauffman Mar 4 '12 at 19:43

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.