What is the purpose of the Microsoft Loopback Adapter?

Question

Just as the question says, what is the Microsoft Loopback Adapter, and as a bonus, what scenerios as a developer would it be useful? I've noticed it's been required when installing a couple of applications to my machine, but aside from guessing, I've never have had a sturdy understanding of it's functionality.

I've read a couple of articles online, but nothing really made me "get it". While I don't need a hugely complex answer, a little explaination would be very useful.

Thanks! George

Answer 1

When sending messages to 127.0.0.1 (or the localhost) the internal network driver typically handles this by shortcutting a few steps.

If you have a networksniffer/protocol analyzer like wireshark, it can not see these shortcutted packets.

By using a loopback adapter, the messages get send much further through the stack, enabling programs like wireshark to capture the packets (and enabling you to analyze the packets)

Answer 2

Well, the best answer I can give you is a few links. http://en.wikipedia.org/wiki/Loopback The key sentence here is

"Any traffic that a computer program sends to the loopback interface is immediately received on the same interface."

http://www.juniper.net/techpubs/software/erx/erx50x/swconfig-system-basics/html/system-mgmt15.html This may be a little more obscure if you don't know networking well.

Basically, it's a fake network interface, useful for tests and stability. In practice, most likely something you'll never have to worry about (or you'd already know about it!)