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?

1 Answer 1


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.

  • 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? Mar 4, 2012 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. Mar 4, 2012 at 18:41
  • I thought you could have one untagged VLAN on a trunk port?
    – Robin Gill
    Mar 4, 2012 at 19:29
  • Yes, that's the Native VLAN Mar 4, 2012 at 19:43

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