Установил 3proxy на ubuntu 24.04 с простейшим конфигом
nserver 8.8.8.8
nserver 8.8.4.4
auth none
log
allow *
proxy -n -p6901
при проверке работы
curl -v -x
x.x.x.x:6901 https://www.google.com
* Trying x.x.x.x:6901...
* TCP_NODELAY set
* Connected to x.x.x.x (77.42.35.66) port 6901 (#0)
* allocate connect buffer!
* Establish HTTP proxy tunnel to www.google.com:443
> CONNECT www.google.com:443 HTTP/1.1
> Host: www.google.com:443
> User-Agent: curl/7.68.0
> Proxy-Connection: Keep-Alive
* Operation timed out after 300493 milliseconds with 0 out of 0 bytes received
* Closing connection 0
порт очевидно снаружи доступен, в логах кроме
251225134121.646 6901 00000 - 0.0.0.0:6901 0.0.0.0:0 0 0 0 Accepting connections [3911/3207919296]
ничего нет.