I am very new to OpenWRT. I have successfully installed and updated OpenWRT onto my old TP-Link Archer C7.
My goal is a dedicated VPN device for devices in my home network to connect to. So I have the ATT modem/router connected to the TP-LInk/OpenWRT wireless router via ethernet from a standard eth port on the provider modem to standard eth port on OpenWRT.
When I run the "update lists" in the GUI or opkg update in cli, they both fail (in GUI is says failed with code 6. CLI just lists the failed "get returned 4" messages.
I feel like this has something to do with DNS, but I'm not sure.
Note that you do not need opkg for debugging, but just nslookup and ping from the router ssh console help a lot. Opkg just uses wget to fetch files, so there is no deeper network logic embedded into it.
You possibly have something in your network settings that is wrong / incompatible with your network topology.
You might explain, how the traffic is expected to flow, what is the lan IP address and subnet of both routers, and show the OpenWrt router's network config file's full contents.