This seems to be something to do with AT&T, blocking VPN ports or protocols or something so I am hoping there is an obvious answer. Are used to be able to turn my personal hotspot on my iPhone on and connect my work laptop to it and then on the laptop log into my company, VPN. Now I cannot do that. I can do ordinary Internet things on the laptop that way, but I cannot get a connection to the company VPN to actually pass traffic. I can do so with no problem at home on the Wi-Fi on AT&T fiber. Or an any coffee shop. Those are all fine but AT&T cellular with hotspot I cannot do it. Is this something where I need to contact AT&T and tell them to open a port for my line to be allowed to use? I already put in a ticket at work, but I know I am just going to get the runaround and they will probably tell me to just find a place with Wi-Fi.
Try visiting this post. Alot have commented on this same issue you’re experiencing.
Yeah but that post basically goes nowhere other than “switch off AT&T to another carrier since AT&T messes with port 443 traffic…”. If that’s still true 3 years later after that post, this isn’t likely to get fixed. And I can just imagine talking to AT&T support on the phone about ports…. OMG.
Yea wouldn’t even waste your time 
Did it ever at any point ever work?
Yeah - worked fine during the pandemic years. Just recently had to work again in a field w/ no nearby Wi-Fi and now I no longer can use AT&T for this. I can visit literally any website I want but cannot VPN through the hotspot. Sigh… I don’t know how people get work done on these things.
Hello, u/CapoKakadan! Thanks for making us aware of this situation with your hotspot and vpn. We want to help!
Have you tried to change your MTU (Maximum Transfer Unit) on your device?
To change the MTU size: Launch a web browser from a computer or mobile device that is connected to your router’s network. Enter the router username and password. The username is admin. Select ADVANCED > Setup > WAN Setup. In the MTU Size field, enter a value from 64 to 1500 (our recommendation is 1320). Click the Apply button.
Please let us know if this resolves the issue. If not, please send us a PM at http://sm.att.com/7cb7bf9a
Our response will be in your inbox found here: http://sm.att.com/f21be2bc
We look forward to hearing back from you! TenielT
Ok, this worked but not the way you suggest (so you may want to amend your support documentation). You asked me to go to my router and change MTU. The scenario I describe is this though: I am sitting in a field of grass next to an AT&T cell tower. My iphone 13 has “personal hotspot” on. My laptop is connected via wifi to my iPhone’s personal hotspot. Internet works fine. VPN on my laptop could NOT work through AT&T cell service via hotspot. So: whose ROUTER are you talking about? I see only grass and a cell tower.
i solved this by lowering MTU to 1320 *in my macbook itself*. Network settings Wifi advanced hardware MTU custom, changed from 1500 to 1320. And now VPN works over iphone over AT&T cellular 5g.
Thank you for making us aware of the process misunderstanding, u/CapoKakadan. We are elated to hear that changing the MTU resolved the issue!
Please don’t hesitate to reach back out in the future if you have any other questions or concerns.
Thank you for choosing AT&T! TenielT