Why VLANs can't be sent over WDS

Installing and Using OpenWrt
1

Before I post the questions, I wanted to clarify that the whole point has become a brainworm for me. After hours in the attic, I've found an RG6 coax that will allow me to trunk the VLANs to an upstairs router over ethernet/MoCA, so I just need the answer for learning / to preserve reminder of my sanity.

I was trying to setup VLAN trunk over WDS backhaul, but couldn't get it to work. I've tried various options, following some manuals, Google Gemini's guide, ChatGPT's. Nothing seems to work. I've read on the forum that WDS doesn't support VLANs and the way to go is either VXLAN or BATMAN adv.

But the question remains, why doesn't it work via WDS? Google search consistently states that WDS essentially is Layer 2 over the air and can do VLANs. How can the info be so wrong? Is it about OpenWRTs implementation? Any help in helping me to understand highly appreciated.

2

Because that is the factt that STA to AP wifi cannot forward vlans.
11sd mash indeed can.
or batman if you plan to wire it up in near future

3

There is a lot of tech stuff involved but the TL;DR short answer is that:

Ethernet packets have a field to carry vlan information but wireless packets do not.

To pass vlan information over wireless, you must encapsulate Ethernet packets inside your wireless packets. This is commonly referred to as a "tunnel" of some sort.

You can build your own tunnel with gretap or vxlan, or use packages designed to to the work for you, eg Batman or Mesh11sd.

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4

One-marc-fifty has some nice instructional video's about using gretap over wireless:

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Alternatively:

  • You could make separate SSIDs for the VLANs on each end (more RF overhead - although, tunnels also create overhead)
  • You could [static] route all traffic (by subnet assigned to each VLAN) via the same SSID at the SRC and route it to the appropriate VLAN at the DST (your traffic isn't isolated over RF using this method)