Newbie in need of help with Arris IP Passthrough and More

Hello! My background in OpenWRT and networking in general is slim to none. Here are my goals, which I am hoping OpenWRT can help with:

  1. I want to use my Linksys WRT3200acm behind an AT&T Fiber gateway (Arris). I don't really want to, but I don't have the option of removing it. I want to interact with and need the Arris as little as possible and use the OpenWRT Linksys moving forward.

  2. I want to utilize a DDNS service for a custom domain I own. It's with

  3. I want to be able to type in my domain name from within my own LAN and have it connect to my home web server. (e.g. minecraft.cooldomain.tld would map to a private IP when connected to the LAN, but otherwise resolve to the public IP address if outside of the LAN) I do not care how this is done, so long as I can do it. Loopback/hairpin/A record/magic, whatever.

  4. I want to have opkg working. Thus far, I can connect to the internet just fine (hello, world), but the ping function in LuCI isn't working, and neither is the opkg function (returns code 7 and thinks I can't connect).

Currently, I have an ethernet cable going from the Arris LAN port to the OpenWRT Linksys LAN port. I keep reading that it should be WAN, but for whatever reason, that breaks my internet connection. I think it may have something to do with AT&T's IP Passthrough function. There is no bridge possibility.

Thanks for tolerating a long post from a newbie. I need all the help I can get! I am comfortable with LuCI and CLI via SSH, though if it's gonna be commands, I would love a line-by-line for what to enter into the interface, as I have zero experience with opkg or OpenWRT in general.

Really appreciate any help!

  1. Bridge mode on the Arris or poor man's bridge.
  2. and
  4. By connecting the lan port of the Linksys to the lan port of the Arris you'll have 2 dhcp servers running in the same network. What is worse is the the OpenWrt does not have a working internet connection so all hosts that get dhcp settings from OpenWrt will be blackholed. The default OpenWrt configuration will work fine in this case, as wan is dhcp client and will get settings from the Arris. And this is what is described in poor man's bridge guide.
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This would be the top item in my TO-DO list. And only after this has been solved, open new threads for each other item.

With the default configuration, if both devices are configured as per common standards, this should work out of the box. The only possible issue I can think of is that both of them have a LAN configured at If that is the case, just reconfigure one of them to