Hello everyone. I am new to this forum and I am relatively new to Linux as well. I am not a complete newbie but I am not a pro as well.

I am now writing my master's thesis related to GMPLS technology that requires implementing a Linux based testbed. In short i am trying to find info about how virtual interfaces in Linux work. There are hundreds of articles about how to configure virtual interfaces, however i couldn't find anything that describes the way it's implemented. Please help.

It's a software thing, purely.
The software sees 2 network cards (etc0.1, eth0.2 or whatever) each with their own IP and netmask and addresses them both through the same hardware.

Thank you for the reply. Yes, I do understand that it's implemented in software, but unfortunately this is not enough for my thesis (. May be someone can advice some literature that may contain info about how virtual interfaces are implemented.

The virtual drivers are implemented in the libraries at the base of the virtual machine. They simulate the network activity within the VM and provide ports for the simulated virtual activity within the VM to become actaul actitivity between non-virtual nodes outside the VM through their access to the host machines adapters and ports.
Within the VM, you can similutate any kind of activity you can imagine and design a driver for. Externally, you're limited to the physical hardware available to the host machine.

Is that what your asking?
If so, you want to do some reading about libvirt, which, as far as I know, is the loweset level library directly dealing with virtualization that has an API.

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Thanks for the answer. This is much closer. However, you refer to virtual machines and network interfaces within the virtual machine. Maybe i was unclear but what i referred to is the ability to use several sub-interfaces on top of a physical. I think it is also called IP aliasing. The point of my work is to investigate how overall performance of a physical interface degrades with huge number of sub-interfaces. Sorry if I caused confusion.

Not as all sa6kad.

IP aliasing works the same way on the virtual guests version of the interface as it does on the corresponding silicon and copper interface of the virtual host.