Microsoft Knowledge Base Article 314053 contains the following introduction:
This article defines all the registry parameters that are used to configure
the protocol driver, Tcpip.sys. Tcpip.sys implements the standard TCP/IP network protocols.
The TCP/IP protocol suite implementation for Windows XP reads all its configuration data from the registry. This information is written to the registry by the Network tool in Control Panel as part of the Setup process. Some of this information is also supplied by the Dynamic Host Configuration Protocol (DHCP) Client service if the DHCP Client service is enabled.
The implementation of the protocol suite should perform correctly and efficiently in most environments by using only the configuration information that is gathered by DHCP and by the Network tool in Control Panel. Optimal default values for all other configurable aspects of the protocols have been encoded in the drivers.
There may be some unusual circumstances in customer installations where changes to certain default values are appropriate. To handle these cases, optional registry parameters can be created to modify the default behavior of some parts of the protocol drivers.
Caution The Windows XP TCP/IP implementation is largely self-tuning. Adjusting registry parameters without careful study may reduce your computer's performance.