Configure TCPIP stack settings in Windows NT
1 January 2001 by Snakefoot | Comment » | Trackback OffTo configure default Receive WINdow (RWIN) in bytes:
To configure default receive window for a single adapter/interface in bytes (Win2k+ only):[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
TcpWindowSize = 17520 (Standard Range = 0-65535, Window Scaling Range 0-1GByte, Default - calculated)
More Info MS KB Q169789
More Info MS KB Q263088
More Info MS KB Q315237
More Info MS KB Q891371
Related : Using PING to find the best TCP/IP RWIN
Related : AFD will adjust the default TCPIP Receive Window
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 \Interfaces \{Adapter-id/GUID}]
TCPWindowSize = 17520
More Info MS KB Q263088
More Info MS KB Q810382
To configure Time To Live (TTL):[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
GlobalMaxTcpWindowSize = 17520 (Standard Range = 0-65535, Window Scaling Range 0-1GByte, Default not set)
To configure Path MTU Black Hole Detection:[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
DefaultTTL = 64 (Range = 0-255, Default = 128)
To configure Path MTU Discovery:[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 KB Q925280
More Info MS KB Q136970
More Info MS KB Q159211
More Info MS KB Q314825
To configure Selective Acknowledgments (ACK's) (Win2k+ Only):[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
EnablePMTUDiscovery= 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]
SackOpts = 1 (Enabled = 1, Disabled = 0, Default = 1)
To configure Max number of Duplicate Acknowledgments (ACK's) (WinNT4 Requires SP2) :[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 KB Q199947
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.[HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services \Tcpip \Parameters]
TcpMaxDupAcks = 2 (Range 1-3, Default = 2)
More Info MS KB Q162179
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 KB Q140552 - Minimize traffic over WAN.
- MS KB Q819108 - Minimize traffic over WAN.
- MS KB Q900926 - Using WAN with MTU less than 576
- MS KB Q120642 - TCP/IP & NBT Configuration Parameters for Windows NT and Windows 2000
- MS KB Q224829 - Description of Windows 2000 and Windows Server 2003 TCP Features
- MS KB Q314053 - TCP/IP and NBT Configuration Parameters for Windows XP
- MS KB Q142641 - Internet Server Unavailable Because of Malicious SYN Attacks
- MS KB Q315669 - HOW TO: Harden the TCP/IP Stack Against Denial of Service Attacks in Windows 2000
- MS KB Q324270 - 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
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Updated: 5 December 2007