[PLUG] Question on OpenWRT and wireless bridging
Ted Mittelstaedt
tedm at portlandia-it.com
Mon Dec 2 01:23:04 UTC 2024
> That is fundamentally why client bridging is a hack
But it's NOT a hack. It's termed "clienT" bridging not "clientS" bridging for a reason - because it's purpose was never to put an entire network of devices behind a wifi AP but instead to make an ethernet-only device into a wifi client.
Where I use it is for VoIP phones. There DO happen to be VoIP phones on the market that have integral wifi chips in them - but they are super expensive. So, a $10 access point + a bit of configuration and voila - a cheap Ethernet-only VoIP phone suddenly now an expensive VoIP phone with a LAN and wifi capabilities.
.
I think the problem with it is like so many things in networking, when it was first implemented the wifi router manufacturers didn't explain what it's purpose was for and just let the market "fill in the blanks"
The ONLY time I've got WDS to ever be reliable is when carefully selecting routers so that they all had the same wifi chip in them, regardless of who manufactured the plastic box the router came in.
This here, is a hack use of a car:
https://www.reddit.com/r/pics/comments/c3p42/redneck_moving_101/?rdt=45016
This here is a proper use of a car:
https://www.freepik.com/premium-ai-image/two-girls-car-with-their-hands-up-driving-summer_58151895.htm
The same thing applies to network devices
Ted
-----Original Message-----
From: PLUG <plug-bounces at lists.pdxlinux.org> On Behalf Of Russell Senior
Sent: Sunday, December 1, 2024 3:00 PM
To: Portland Linux/Unix Group <plug at lists.pdxlinux.org>
Subject: Re: [PLUG] Question on OpenWRT and wireless bridging
On Sun, Dec 1, 2024 at 2:32 PM Ted Mittelstaedt <tedm at portlandia-it.com> wrote:
>
>
> Until recent kernels, Broadcom has supported client-bridging in it's
> wifi binary blob drivers. THAT is why historically dd-wrt has been so
> solid with client bridging - since it happens in the driver layer, not
> in the kernel or userspace. I can understand why, if you only have
> used OpenWRT, that you are so down on client wifi bridges. [...]
Normal infrastructure mode wifi (AP and clients) only uses three mac addresses in the frame header. When a client sends a frame, there is a MAC address for the AP and the MAC address for the destination, and the source and station MAC are conflated. When the AP sends back to the station, it ONLY knows that conflated MAC address. If the destination is really somewhere behind the station, it never gets there. That is fundamentally why client bridging is a hack. WDS uses 4 MAC addresses in the frame and works, but the AP needs to be "in on it". That is all baked into the 802.11 standard. So, client bridging involves playing tricks with MAC addresses, A frame arrives on the client wifi MAC address, but ... what is its real destination? The client bridge doesn't really know. The hacks involve guessing, and that guessing ultimately breaks something.
--
Russell Senior
russell at personaltelco.net
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