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
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!)
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)
Here's an explanation that might be a bit easier to understand - one I'm working on at the moment.
We (a Bank) are pretty damn secure, as you would expect. One of our third party vendors requires the POS java app that we have to use connect to a 172.x.x.x address. Well, that's not routable.
So we have loopback adapters, one for each of their 172.x.x.x addresses, with the address we will allow as the IP. We then use the "netsh" command to redirect traffic...
So any traffic that access, for example, 172.1.1.1 will get intercepted by Loopback Adapter #1 and redirected to 10.2.2.2. The pain is having one adapter per address.
Hope that makes it a little clearer.
Some software requires some network functionality, even if the machine in question doesn't have network functionality. The loopback is a dummy network driver, which can have real network protocols bound to it. This allows the software to install properly, even though there isn't a real network card installed in the machine.
It is mostly used if you have programs that have an expiration date, so that it keeps working.
来源：https://stackoverflow.com/questions/2021415/what-is-the-purpose-of-the-microsoft-loopback-adapter