Proxy on one ip through 3g modems. How to organize?

Question

linux

There is a server on debian.
The Internet is connected to it with a real ah pi.
Also, two 3g "whistles" are plugged into it.
How can I configure it so that the user registers an IP from the wired Internet and, depending on the specified port, accesses the Internet from different IPs through 3g modems?
I would like to end up with a couple of proxies of this kind.
111.111.111.111:3128 - out through Life
111.111.111.111:3129 - out through Kyivstar
3g "whistles" started as separate interfaces with IPs 192.168.8.100

Answer 1

the easiest way is a specific domain through a specific interface
sudo ip route add {domain_ip} via {remote_ip} dev {interface}
with a proxy, due to different OSI levels, the game is more fun, at least marking traffic on ports
https://unix.stackexchange.com/questions/ 21093/out...
https://serverfault.com/questions/565165/squid-spec...