RT-AX86U suddenly "ISP's DHCP does not function properly"; RT-AC68U works fine on same modem port

[Dick_W]

(Also posted in the RT-AX86U 3.0.0.4.388_24386 thread. Hopefully duplicating it here will get it more visibility and maybe somebody will have some ideas.)

I installed 3.0.0.4.388_24386 on my RT-AX86U last week, then did a factory reset and hand reconfigure of everything. (Sigh. If not for the broken certs and all of the client names to be fixed, this wouldn't have been so bad.) It worked fine until early this morning. Now it's saying "Your ISP's DHCP does not function properly" and not connecting. ISP is Hawaiian Telcom, modem is a Nokia G-240G ONT. No message in the router log gives any hints what the WAN DHCP problem might be.

I've rebooted everything and power cycled everything. No Joy.

I called HawTel and they said "works fine here, must be your router".

To try this, I dusted off my spare RT-AC68U and set it up, while connected to the modem. It came up connected to the ISP just fine, first time, no special magic. Reconnect the AX86U. No Joy. Same error. I've tried resetting/cycling through various AX86 WAN settings and have tried swapping the AX86 2.5G WAN connection vs 1G WAN connection. And using a different cable from modem to router WAN port. All with No Joy.

Any thoughts?!?

 

[dave14305]

Try to clone the MAC address from the AC68U to the AX86U on the WAN page and see if it helps get you back up and running.

 

[Dick_W]

I'd already tried a proxy MAC just shifting the AX86's MAC by one digit--didn't have the AC68's MAC handy. Just tried the AC68's MAC. Still No Joy. I'm probably going to try another factory reset tomorrow, for lack of anything else left to try. What a PITA.

 

[degrub]

You may have to reset the ISP connection to the ONT by leaving power off for 10 minutes.
Factory reset the AX and leave it powered off. Once the ISP ONT is up, connect the AX, power up and run the ASUS WAN connection wizard if available..

 

[Dick_W]

I did ultimately get this working again, but, disappointingly, I'm not really sure what the root cause was. I was almost convinced it was enabling jumbo frames but re-enabling them once it was all back working didn't (yet?) break ISP DHCP. Maybe it will faceplant again when my lease expires on the DHCP info it got before I enabled the jumbo frames?

 

[degrub]

MTU might affect the connection to the ISP device. Jumbo frames on the LAN side should be translated, albeit with likely fragmentation and latency created.

 

[jksmurf]

Not any help but I’ve had that same error message occasionally, maybe once a year. The odd thing is it flashes up with everything looking ok, then shows the disconnected symbol and that message.

Only powering off waiting and rebooting both ONT and router several times ever fixed it for me. No changes in any settings (I view it as why should there be if it worked before). Similar to the OP, I really don’t know what fixed it when I got it going again. Mystery.

 

[iFrogMac]

Is it related to certain providers? I've had my RT-AX86U since 2022, and while I've had my quirks with it, I've never had this particular issue, and it's been a pretty common one reported for this router. I should mention, I've only used it with two providers. Spectrum, and Cox.