IP phones behind NAT on TCP

Hello everyone! Hope all are having a great holiday break.

Cloud hosted FreePBX with a couple remote Yealink phones (home users).

We had a lot of NAT issues because one of the home user’s router just does not work with VOIP properly. So we had to put it on openvpn which worked but, it added another layer of problems to come up when the vpn connection would stop working for whatever reason.

I have heard that moving the IP phones to TCP rather than UDP could fix some NAT issues. We have tried that and indeed, both phones behind the same home router are now reachable on the same network. In fact, two different extensions on the same phone are still reachable without any NAT issues.

My question is, is this expected that TCP can fix this? Will this keep working in the future? It seems to be working great on TCP!

Let me know what you guys think.


My understanding is that the ISP is probably handling the UDP traffic in a negative way as opposed to TCP. Wish I had more information, but that’s all I know. (cgnat in play?)

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