Fiddler and IPv6-only environments

I recently got a bug report from a user who was attempting to use Fiddler in a pure-IPv6 environment, where IPv4 is entirely disabled. On startup, he saw the following message: The problem here is an obscure one, which makes it somewhat interesting. What’s happening is that Fiddler is trying to create an IPv4 listener…

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Mapping Sockets to a Process In .NET Code

One feature added to Fiddler a few years ago is the ability to map a given HTTP request back to the local process that initiated it. It turns out that this requires a bit of interesting code, because the .NET Framework itself doesn’t expose any built-in access to the relevant IPHelper APIs that provide this…

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Fiddler New Features – DNS Failover

Fiddler 2.2.9 introduces a ton of new features under the hood. The one I’m going to talk about in this quick note is called “DNS Failover.” When a client attempts to connect to a web server, it must first resolve the hostname of the server (e.g. www.example.com) into an IP address to which a TCP/IP…

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