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I am still new to VLANs and the concept, so please bear with me...

We have a core switch to handle all of our traffic, then other switches are connected to the core switch from different areas of the building. I'd like to use VLANs for different areas, but it includes devices that cannot add a VLAN tag to the packets (i.e. printers).

If I set the Uplink Port (usually Ports 1&2) to be TAGGED VLANs for all the VLANs I need, can I set certain ports goign to devices to be UNTAGGED, and have the traffic route through the correct VLAN?

Core Switch  ==========Switch 01
VID 1,10,20,...        P1/2 - TAGGED VLAN 1,10,20,...
                       P5   - UNTAGGED VLAN 10 <== Will this get tagged when it leaves?
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  • I am curious about your claim that you daisy-chain the switches. Do you mean that traffic for each switch has to pass through all the previous switches to get to the core switch? That would be an extremely bad scenario. Each access switch should directly connect to the core switch, and the core switch should be configured as the root bridge.
    – Ron Maupin ♦
    Oct 14, 2016 at 17:15
  • @RonMaupin Yes, you are correct. Not daisy-chained. I want to say Hub-and-Spoke, but I don't know if that's even the right term now...
    – Canadian Luke
    Oct 14, 2016 at 17:28
  • I would call it a physical star topology. The logical topology with VLANs could be different.
    – Ron Maupin ♦
    Oct 14, 2016 at 17:29

2 Answers 2

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Short answer: Yes

Tagged and untagged frames are different formats. The switch will convert from one to the other as necessary.

When you set a port to "Untagged VLAN 10" (switchport access vlan 10 in Cisco-speak), a frame entering that port is associated with VLAN 10. If the frame is forward out a port that is tagged, the frame is converted to 802.1q format, which includes a VLAN tag.

The process also happens the other way: a frame received on a trunk port with a VID of 10 will be forwarded out the untagged port as a "regular" Ethernet frame.

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You should tag frames on trunks between switches. Most end-devices don't understand VLAN tags. Some servers do, but, again, you tag the frames only on a trunk to such servers.

Access interfaces don't tag frames. The reason to tag frames is so that a trunk with frames from multiple VLANs can distinguish which frames belong to which VLANs. Access ports only have one VLAN, so there is no reason to tag frames on an access interface. You only set the VLAN for the access interfaces, but do not tag frames for those interfaces.

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