DHCP completely broke on my RUTX11. I want to share knowledge about this behaviour, because it was a massive time sink.
I had my RUTX11 as a wifi access point, with DHCP provided by another device (opnsense).
I had three interfaces in the LAN firewall zone (core/client/guest), each on its own subnet. I had three SSIDs, two for trusted clients and a guest SSID. Client isolation was enabled on the guest SSID but not the client SSIDs.
I had them in the same zone because I have no interest in firewalling on the RUTX. I want my lans on separate VLANs and I want to let the opnsense apply ACLs. Unfortunately, you cannot turn off firewalling on the RUTX, AFAICS. If this is possible, please let me know.
This worked fine for weeks - much longer than the DHCP lease time! Then the guest WLAN broke while the client WLANs still worked. I found nothing in the RUTX logs to provide any hint. Finally I rebooted the device and found that DHCP was completely broken on all WLAN interfaces.
Throughout this issue, layer 2 broadcast did work. When I set a static IP on the wlan client, I got arp from the wired segment.
My opnsense logs didn’t even show the DHCP broadcast packets coming in. I should not have needed to set up DHCP relay, since the rutx11 interfaces were on the same subnets as the corresponding opnsense interfaces, but DHCP relay didn’t work either. Neither did Force.
In fact, setting up DHCP server on the rutx also didn’t work! It was as if the rutx was discarding the broadcast frames at the wifi interface.
No matter what DHCP configuration I tried, DHCP frames were silently discarded.
This behaviour was shown on 7.06, 7.08 and 7.10.
Finally, I found this post about the RUT241: DHCP with two LAN interfaces not working
I had no reject rules in my firewall config. All of these interfaces were in the LAN zone. There was no reason, by config, that the frames should have been dropped. However, I rebuilt the config from scratch, AGAIN, by hand through the web UI, AGAIN, and this time I put core/client/guest in different firewall zones. Now DHCP works. Frames are forwarded as expected. When I turn on DHCP server in the rutx, that works too.
It has now been stable for three days, but I’m done with OpenWRT. I’d love to support Teltonika again, but not while the product range is based on OpenWRT. It really shows its roots in residential equipment when you want to configure ACLs, routing, and firewalling. I am not the target market, I guess. Perhaps I’d be more favourable if I had to support a dirty warehouse in a distant industrial zone.
I hope this saves someone else some time.