INF: Http.sys Registry Settings for IIS (820129)

SUMMARY

In Microsoft Windows Server 2003, Http.sys is the kernel mode driver that handles HTTP requests. Several registry values can be configured according to specific requirements. The table in the "More Information" section contains the following information about these registry values:

Registry key names
Default values
Valid value ranges
Registry key functions
WARNING codes (where appropriate)

Note See the "WARNING Codes" section for information about potential risks when you create and configure registry values by using settings other than the default settings.

This article is intended for advanced users and assumes knowledge of the registry and of the risks that are involved when the registry is changed.

MORE INFORMATION

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
You can create the following DWORD values under the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters key:

Registry Key	Default Value	Valid Value Range	Registry Key Function	WARNING Code
AllowRestrictedChars	0	Boolean	If non-zero, Http.sys accepts hex-escaped chars in request URLs that decode to U+0000 - U+001F and U+007F - U+009F ranges.	0
EnableNonUTF8	1	Boolean	If zero, Http.sys accepts only UTF-8-encoded URLs. If non-zero, Http.sys also accepts ANSI- or DBCS-encoded URLs in requests.	0
FavorUTF8	1	Boolean	If non-zero, Http.sys always tries to decode a URL as UTF-8 first; if that conversion fails and EnableNonUTF8 is non-zero, Http.sys then tries to decode it as ANSI or DBCS. If zero (and EnableNonUTF8 is non-zero), Http.sys tries to decode it as ANSI or DBCS; if that is not successful, it tries a UTF-8 conversion.	0
MaxConnections	MAX_ULONG	1024(1k) - 2031616 (2MB) connections	Overrides the MaxConnections calculation in the driver. This is primarily a function of memory.	1
MaxEndpoints	0	0 - 1024	The maximum number of current end point objects that are permitted. The default value of zero implies that the maximum is computed from available memory	1
MaxFieldLength	16384	64 - 65534 (64k - 2) bytes	Sets an upper limit for each header. See MaxRequestBytes.	1
MaxRequestBytes	16384	256 - 16777216 (16MB) bytes	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.	1
PercentUAllowed	1	Boolean	If non-zero, Http.sys accepts the %`uNNNN` notation in request URLs.	0
UrlSegmentMaxCount	255	0 - 16,383 segments	Maximum number of URL path segments. If zero, the count bounded by the maximum value of a ULONG.	1
UriEnableCache	1	Boolean	If non-zero, the Http.sys response and fragment cache is enabled.	0
UriMaxUriBytes	262144 (bytes)	4096(4k) - 16777216(16MB) bytes	Any response that is greater than this value is not cached in the kernel response cache.	1 3
UriScavengerPeriod	120 (seconds)	10 - 0xFFFFFFFF seconds	Determines the frequency of the cache scavenger. Any response or fragment that has not been accessed in the number of seconds equal to UriScavengerPeriod is flushed.	1 2
UrlSegmentMaxLength	260	0 - 32,766 chars	Maximum number of characters in a URL path segment (the area between the slashes in the URL). If zero, it is the length that is bounded by the maximum value of a ULONG.	1

WARNING Codes

0: No risks.
1: Changing this registry key is considered extremely dangerous. This key causes Http.sys to use more memory and may increase vulnerability to malicious attacks.
2: A low value may cause the cache to be flushed more frequently. If this behavior occurs, it may affect performance.
3: A low value may affect performance for static content.