How to access the Internet on a specific Internet connection if there are several Internet connections?

Question

linux

Greetings!

There is: a computer (windows / linux to choose from) with several usb inputs, each with a usb / sim modem. Accordingly, there are several Internet connections on the computer at the same time.

Question: how to log out in an Internet program in C # on a specific Internet connection. At the same time, other programs that use other Internet connections should not lose access to the Internet.

Several virtual machines: creating several virtual machines, having 1 Internet connection in each, and running the necessary software in each is not suitable . For periodically, you need to go online from another Internet connection ...

In which direction to dig, what to read?

Answer 1

On Linux, it is possible to handle routing for tagged traffic through the iproute2 package.
If you can mark traffic from a specific application, for example via iptables -j MARK, then it can then be "rerouted" to any outgoing interface.