Cannot host netplay, but can join

[00DUMB]

I am able to join friend's netplay sessions without issue. However, I am unable to host sessions in either transversal or direct mode. The host launches fine, but no one can see me. Running 'netstat -a' in CMD shows that the relevant port is not listening, unlike when hosting a different application using that port (not simultaneously, of course). I'm at a loss, and my troubleshooting leads me to the same issues that I have already resolved. Things I've already covered:

• Administrator mode doesn't change anything
• Application firewall exception doesn't change anything
• Disabling firewall all together doesn't change anything
• Port is correctly forwarded and viewable via canyouseeme.org using a different application
• Toggling the UPnP option in the netplay window doesn't change anything.
  

My network device is a BGW320-505 from AT&T. Not sure if there's a dumb setting on it that needs to change; I had to do that once already for git purposes, so it wouldn't surprise me.

Thanks in advance!