Hello all!
First post here, and I have done days(actually weeks) of searching, but if this is in the wrong place or has already been covered, please let me know and I will be happy to move/read anything relevant.
Before we get into this, I am an IT guy with 20+ years of experience. I ran a pen testing company for years (where I was the lead tech), I own and teach in a post-secondary school that teaches networking and security, and I have a background in operating a myriad of networking systems. I say this to help you understand where I am coming from, and to let you know that you can get as "geeky" as you want with me, and I will understand, or ask if I don't.
OK, going to provide as much info as I can:
I have a ZBT device (WG-1608) running the WiFix firmware, which is OpenWRT with a couple additions.
This device has a Quectel RM502Q-AE installed, and all firmware/drivers/software are up to date. I use this to connect to a T-Mobile signal. I am using MBIM to communicate with the modem.
I also have a MoFi device that connects to the same signal. It works without any issues, except that it doesn't connect to 5G and thus is considerably slower. About 1/3 the speed of the ZBT.
The ZBT device is up the hill from my house, about 1/2 mile and 1400' of elevation and get's line of sight to the tower. It connects to a Point-to-Point link that sends the signal here(to the house), which then connects to a ubiquiti switch and several AP's. All the devices then connect through these AP's.
The issue is this:
WiFi calling will not enable from any phone in the house. I have several T-Mobile phones, an unlocked phone with a T-Mo SIM, an AT&T phone, and 2 Verizon phones. Also, I can not connect with UDP to another server I have setup in another location (I host a Valheim server, and it uses UDP, just in case that's somehow relevant). If I switch to the MoFi everything works flawlessly (albeit a lot slower), so I have isolated the problem to this device. If I connect directly to the ZBT with either WiFi or Ethernet, I experience the same issues, and if I replace the ZBT with the MoFi, everything works, thus ruling out any network issues, although the network setup is VERY basic anyway. I have also replaced the ZBT with another identical device to rule out a hardware issue, and they both have the same problem. Unless they both have the same hardware malfunction, which I find unlikely...
WiFi calling works by setting up an IPSEC tunnel to a remote server, which also uses UDP to establish the connection (ISAKMP+ESP). I have the firewall on the ZBT setup in it's default config, so the stateful setup should be facilitating this, but it apparently isn't. I have played with different settings to try to get this working, including NAT and different firewall rules, but at this point have reset everything back to stock. I also experience intermittent connectivity drops. For example if I watch download traffic, it will download for 1-2 secs, then stop for 1-2 secs then download again for 1-2 secs, then stop for 1-2 secs. This behavior repeats ad-nauseam.
I am completely out of ideas, and this is a last resort to make this post. Hoping someone out there has experienced this, or has a simple and easy solution I just haven't thought of! Any help is appreciated!!
Thanks in advance!