What is the purpose of the Microsoft Loopback Adapter?

localhost loopback
George Johnston picture George Johnston · Jan 7, 2010 · Viewed 81.4k times · Source

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

Toad picture Toad · Jan 7, 2010

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)

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