Difficulties with port forwarding AC1750 behind BGW210-700 gateway

I have two services running on ports 25565 and 8123 on my local machine, and I'm trying to expose them publicly on a TP-Link AC1750 running OpenWrt 21.02.1. My biggest obstacle is this dumb BGW210-700 gateway that AT&T makes us use, which has been complicating things.

My goal is to get port forwarding working properly. Here's what I've done so far:

  • Connected the BGW210 gateway to the AC1750 via a LAN ethernet port.
  • Put the BGW210 gateway into passthrough mode, DHCPS-fixed, set to the AC1750's local IP.
  • Disabled all firewall options on the BGW210 and disabled router cascade
  • Set the gateway in OpenWrt on the AC1750 to the BGW210's local IP.
  • Set up port forwarding rules on the AC1750 to forward from the specified ports on LAN to the server machine's IP on LAN.
  • Set up matching port forwarding rules on the BGW210's settings (otherwise, the ports aren't seen as open at all on canyouseeme.org.)

After all this, the ports are visible as open to external port checkers, but any attempt to actually access the servers running on those ports from the external IP fails. They can be connected to via the local IP, but fail when accessed through the external IP.

Does anyone have any advice for what I'm doing wrong here or what I should do differently? Please let me know if more information is needed.

Disregard this, I ended up pseudo-fixing this by eliminating the double NAT by just doing port forwarding on the gateway. It's still behaving strangely sometimes, but at least it connects now.

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