To configure the TCPIP stack for optimal performance, then it is recommended to use utilities like DrTCP or TCPIP Optimizer especially if not feeling comfortable with the registry editor.

To configure default Receive WINdow (RWIN) in bytes:

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
TcpWindowSize = 17520 (Standard Range = 0-65535, Window Scaling Range 0-1GByte, Default - calculated)

More Info MS KB169789
More Info MS KB263088
More Info MS KB315237
More Info MS KB891371

Related : Using PING to find the best TCP/IP RWIN
Related : AFD will adjust the default TCPIP Receive Window

To configure default receive window for a single adapter/interface in bytes (Win2k+ only):

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters \Interfaces \{Adapter-id/GUID}]
TCPWindowSize = 17520

More Info MS KB263088
More Info MS KB810382

To configure maximum receive window size for all interfaces in bytes. To ensure that Window Scaling doesn't create receive windows that takes too much memory (Win2k+ Only):

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
GlobalMaxTcpWindowSize = 17520 (Standard Range = 0-65535, Window Scaling Range 0-1GByte, Default not set)

To configure Time To Live (TTL):

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
DefaultTTL = 64 (Range = 0-255, Default = 128)

To configure Path MTU Black Hole Detection:

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
EnablePMTUBHDetect = 0 (Enabled = 1, Disabled = 0, Default = 0)

Note Windows 2003 SP2, Windows XP SP3 and Windows Vista enables black hole detection by default, and changes the PMTU to 536 bytes if retransmissions occurs (If the following retransmission also fails then the PMTU is returned to its original size). More Info MS KB925280

More Info MS KB136970
More Info MS KB159211
More Info MS KB314825

To configure Path MTU Discovery:

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
EnablePMTUDiscovery= 1 (Enabled = 1, Disabled = 0, Default = 1)

To configure Selective Acknowledgments (ACK's) (Win2k+ Only):

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
SackOpts = 1 (Enabled = 1, Disabled = 0, Default = 1)

To configure Receive Window Scaling and Time Stamping (Win2k+ Only):

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
Tcp1323Opts = 3 (Both Disabled = 0, Window Scaling Only = 1, Timestamp Only = 2, Both Enabled = 3, Default = No value; only initiate the options if requested.)

More Info MS KB199947

To configure Max number of Duplicate Acknowledgments (ACK's) (WinNT4 Requires SP2) :

[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
TcpMaxDupAcks = 2 (Range 1-3, Default = 2)

More Info MS KB162179

Note none of these registry entries can be found in the registry after a clean install, so to return to the default values just delete the registry entries.

Related Delayed TCPIP ACK can cause slow network throughput
Related Configure the max limit for concurrent TCP connections

More articles about the settings available for configuring the tcpip stack:

• MS KB140552 - Minimize traffic over WAN.
• MS KB819108 - Minimize traffic over WAN.
• MS KB900926 - Using WAN with MTU less than 576
• MS KB120642 - TCP/IP & NBT Configuration Parameters for Windows NT and Windows 2000
• MS KB224829 - Description of Windows 2000 and Windows Server 2003 TCP Features
• MS KB314053 - TCP/IP and NBT Configuration Parameters for Windows XP
• MS KB142641 - Internet Server Unavailable Because of Malicious SYN Attacks
• MS KB315669 - HOW TO: Harden the TCP/IP Stack Against Denial of Service Attacks in Windows 2000
• MS KB324270 - HOW TO: Harden the TCP/IP Stack Against Denial of Service Attacks in Windows Server 2003
• MS Technet - Microsoft Windows 2000 TCP/IP Implementation Details Word Document
• MS Technet - Microsoft Windows Server 2003 TCP/IP Implementation Details
• MS Technet - Security Considerations for Network Attacks
• MS Technet - Performance Tuning Guidelines for Microsoft Services for Network File System
• TCPIMP2.EXE & TCPIPIMP.EXE - WinNT TCPIP Whitepapers Mirror

Credits regedit.com