Using Fiddler to check IIS Compression

Question

How do I see if IIS Compression is working using Fiddler? I have a page that, when viewed through Port80Software or GID Network's tool it appears to be coming across compressed.

However, when I watch the call in Fiddler, I see the 'Accept-Encoding: gzip, deflate' in the request header, but I don't see the 'Content-Encoding: gzip' or 'deflate' in the response header. Also, in the Transformer section, 'No Compression' is selected.

Thanks!

Chris

Answer 1

My version of fiddler has and AutoDecode button that made everything appear to have No Compression. After turning this off, my responses showed compression

Answer 2

I went straight to the source (to Eric Lawrence) and this is what he said:

Indeed, Fiddler shows your site is compressing properly.

Do you have an upstream proxy server in your environment? Did you try this test from your home network rather than your corporate network?

On Microsoft’s corporate network, we are all behind an ISA proxy server. It’s configured to remove the outbound Accept-Encoding header (which tells servers to use compression) and if a compressed response is received by the proxy, it’s decompressed by the ISA server. This is done so the ISA proxy server can scan the content for malicious data. The downside is that Fiddler is only seeing the traffic as it’s received from the upstream proxy.

Usually, when we need to test compression and the like, we do so from home or what’s called a “DTAP”—a direct line to the internet that doesn’t go through the proxy.