IIS 6 seems to be limited (by default at least) to an http header of 16k. I have a 3rd party tool that is talking to the web server (ajax) and sending an http header that is bigger than that. Since I can't control the 3rd party tool, I am hoping to find an IIS 6 setting that will let me increase the maximum header size to 32768 or whatever.

1 Answer 1


Look at the value in


This value determines the upper limit of the request header, although there are caveats. From TechNet:

Determines the upper limit for the total size of the Request line and the headers. Its default setting is 16KB. If this value is lower than MaxFieldLength, the MaxFieldLength value is adjusted.

Changing this registry key is considered extremely dangerous. This key causes Http.sys to use more memory and may increase vulnerability to malicious attacks.

Here is the TechNet article with more information, including other tuning parameters.

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