How to connect/bridge two subnets within the same router

I'm not seeing anything obviously wrong in your basic configuration, but I did find two things of interest:

And and old bug: https://github.com/openwrt/openwrt/issues/6089

@psherman I see. Does this mean my router cannot use the 5Ghz channel in the AP mode and client mode at the same time?

It seems that way. The first thing I linked indicated that the upstream was a DFS channel and that was why it didn't work... but that may or may not be the case in your situation (FWIW -- what channel is the upstream? and what region are you in?)

The second thing was a bug that was quite old, so I don't know if that still exists and/or if it was hardware or software limited (or a true bug in software).

@psherman I am in the United States. I checked my wifi settings and both the upstream and downstream are set to the United States. I set both the upstream channel and downstream channel to "auto". But the problem still exists and my laptop cannot find "openwrt" wifi. I also tried to set both the upstream and downstream to a same channel manually, like channel 52 or channel 124 (I checked the best channel using my laptop before changing the channel). However, this approach does not work. Openwrt shows "wireless is not associated".

I also found a link here:

It says this router does support the repeater/bridge mode using the same 5Ghz channel. I also called Tp-link to confirm this. The company says its original tp-link archer a7 ac1750 supports the repeater mode and can use the 5GHz channel for upstream/downstream at the same time. So, possibly this is a limit/bug of openwrt?

Thanks

I think I may have added some confusion. The channel must be 'auto' in order to allow the radio to connect to the upstream network. That same channel will then be used for the downstream.

The question is what channel is being used for the upstream network -- if it happens to be one that is in the DFS range, that will cause some additional complications with respect to operating in AP mode on that channel. (the question about region is relevant because the DFS channels are different in various parts of the world)

If you connect directly to the upstream network, you should be able to see what channel is in use.

It is possible that there is a bug or limitation in OpenWrt even if the hardware supports it... I can't say. I'm not an expert of the wifi radio devices in OpenWrt, so hopefully others can chime in here.

@psherman I agree with you that both the upstream and downstream channels should be set to "auto". When they are set to "auto", the "wireless is not associated" problem disappears.

Now, I feel this most likely is caused by a OpenWrt limit/bug.

Just to clarify, 'auto' channel selection is effectively a requirement for connecting to upstream networks (I mean, if you know the channel, you can specify it, but that only works if that is always correct -- if the upstream side changes, your network goes down).

And the other element here is that a wifi radio used in sta + AP modes cannot come up in AP mode until it has connected to the upstream (sta mode) because this dictates the channel that will be used. As a result, if the channel is manually specified and is wrong (or if the upstream AP is not available), the downstream AP cannot start. That is why the travelmate package was developed.

Now, if everything is working properly on the upstream connection and your device is still unable to bring up the AP mode, this could very well be a bug/limitation of OpenWrt. A bug is certainly possible, but I don't know if the same bug I linked is still relevant.

In some cases, the functionality for this is supported in hardware and in the closed source vendor firmware, but if those libraries are closed source, they can't be included in OpenWrt -- in this case, it's not a bug, but a driver limitation due to not having open source code.

I also want to point out a curious statement from your conversation with TL-Link:

I've added emphasis to the word "original" because I wonder if it is possible that later versions dropped that capability due to a hardware change or other reason... I don't know, just raising this as a question.