2000, XP and Vista are configured with priority to Ethernet rather than high-speed Internet connections where latency plays a major role in throughput. Here, you will find specific information on how to optimize the Windows 2000 and XP registry for Cable Modems, DSL, or any similar type of broadband Internet connection.

Customizing the Windows Registry assumes some proficiency in tuning Windows configuration files. If you don't feel comfortable editing the Registry, then please use this file Win2000_XP_DSL_Tweaks.reg the file contains the settings required to automaticaly make the changes to your registry.Just click on the link and save the file to your local drive, when prompted import the registry settings. It is strongly recommended that you backup your Registry before editing.

If you'd rather make the changes yourself, or prefer to experiment with different values to fine-tune your connection, follow the directions for editing the Registry below.

Editing the Windows 2000/XP Registry
To edit the Registry, you need to use an editor, such as Regedit. As with previous Windows versions, it can be accessed from the Start Menu ( START > Run > type "Regedit" ). Note that most of the values recommended on these pages are not present in the Registry by default and you might have to add them manually. Also, for most of the tweaks to take effect you must Reboot.

It is strongly recommended that you backup your Registry before editing. The easiest way to backup your Registry is from within the Registry Editor, just choose "Export Registry File" from the pull-down menu

Recommended settings for Windows 2000 / XP
Windows 2000 and XP supports large windows as described in RFC1323 ( the 'RcvWindow' has a maximum value of 2**30 rather than 64K), and includes some other improvements over its predecessors you can use to speed up any TCP/IP transfers. The best settings are listed in red, the descriptions and other options are added to provide you with better understanding and enable you to customize your settings.

All the following entries, unless otherwise noted should be placed in the Windows 2000 or XP Registry under the key

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

TCPWindowSize
The value of TCP Window in the Windows 2000 Registry is DWORD, representing number of bytes, with range from 0 to 2^30. The recommended values (in red) optimize TCP for any high speed Internet connection and work best in most cases, however if you'd like to use a custom value follow these guidelines:

For best results, the TCPWindow should be a multiple of MSS (Maximum Segment Size). MSS is generally MTU - 40, where MTU (Maximum Transmission Unit) is the largest packet size that can be transmitted. MTU is usually 1500 (1492 for PPPoE connections). To determine the MTU value of your ISP, check out the Advanced Registry Editing section of our site.

There are three places in the Windows 2000 Registry where you can add the TCP Window parameter.

HKLM/SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
GlobalMaxTcpWindowSize="256960" (DWORD, number of bytes) Valid range is from MSS to 2^30. Add the value as a decimal. Note: For best results RWIN has to be a multiple of MSS lower than 65535 times a scale factor that's a power of 2, i.e. 44 x 1460 = 64240 x 2^2 = 256960. If you choose to use a RWIN lower than 65535, you can simply make it multiple of MSS and turn scaling off (Tcp1323Opts=0)

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
TcpWindowSize="256960" (DWORD, number of bytes) Valid range is from MSS to 2^30. Add the value as a decimal. TcpWindowSize can also exist under TcpipParametersInterface - if added at this location, it overrides the global setting for this particular . Note (10/20/00): Seems MS has found another bug in Windows 2000, the TCPWindowSize should be configured with the global setting (GlobalMaxTcpWindowsSize) rather than this one - Q263088

Tcp1323Opts
Tcp1323Opts is a necessary setting in order to enable Large TCPWindow support as described in RFC 1323. Without this parameter, the TCPWindow is limited to 64K.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Tcp1323Opts="1" (DWORD, recommended setting is 1. The possible settings are 0 - Disable RFC 1323 options, 1 - Window scaling but no Timestamp options, 3 - Window scaling and Time stamp options.)

DefaultTTL
DefaultTTL determines the time in seconds and the number of hops a packet lives. While it does not directly affect speed, a larger value increases the amount of time it takes for a packet to be considered lost, discarded and retransmitted. A value that's too small can cause packets to be unable to reach distant servers at all.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
DefaultTTL="64" (DWORD, recommended setting is 64. Other settings that are widely used are 128 and 32)

EnablePMTUDiscovery
When set to 1 (True), TCP attempts to discover MTU automatically over the path to a remote host. Setting this parameter to 0 causes MTU to default to 576 which reduces overall performance over high speed connections. Note that this setting is different than our Windows 9x recommendation.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
EnablePMTUDiscovery="1" (DWORD - boolean, valid settings are 0-->False and 1-->True. Many connections perform better with this entry at 1, however, if you prefer to set your upstream to send fixed 1500 packets, you might want to use 0 instead). When set at 1, establishing connections and initial transfer speed might slow down a bit, however you will get better throughput if somewhere in the path large packets need to be fragmented.

EnablePMTUBHDetect
Setting this parameter to 1 (True) enables "black hole" routers to be detected, however it also increases the maximum number of retransmissions for a given segment. In most cases you'd want to keep BHDetect to 0 (False).

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
EnablePMTUBHDetect="0" (DWORD - boolean, valid settings are 0-->False and 1-->True. Recommended setting is 0)

SackOpts
This parameter controls whether or not SACK (Selective Acknowledgement) support is enabled, as specificationified in RFC 2018. SACK is especificationially important for connections using large TCP Window sizes.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
SackOpts="1" (DWORD - boolean, recommended setting is 1. Possible settings are 0 - No Sack options or 1 - Sack Option enabled).

TcpMaxDupAcks
This parameter determines the number of duplicate ACKs that must be received for the same sequence number of sent data before "fast retransmit" is triggered to resend the segment that has been dropped in transit.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
TcpMaxDupAcks="2" (DWORD - range 1-3, recommended setting is 2).

Additional TCP/IP Related Parameters

The additional TCP related parameters are not necessary in most cases, and you shouldn't expect any drastic improvements, however we added them for those of you who like experimenting. You might be able to gain that last bit of performance, or customize your TCP/IP behavior even more with those. Keep in mind you should familiarize yourself with what the parameters mean and how they affect your connection before changing their values

MTU
Setting MTU overrides the default MTU for the network interface it is added to. Note that if EnablePMTUDiscovery is set to 1, TCP will use the smaller value of this local MTU and the "Discovered" MTU of the underlying network connection. If you'd rather use only the MTU value specificationified here, you'd have to disable PMTUDiscovery, which would prevent your system from detecting the network MTU.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces
MTU="1500" (DWORD, valid range is from 68 to MTU of network).

Note: For Windows XP PPPoE, there is an additional location for MTU that might need to be adjusted (to 1480, or up to 1492 as per the PPPoE specifications), depending on the PPPoE software you use. Check the following location in the Registry:
HKLM\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols\0
ProtocolMTU="1480" 

Windows 2000 Web Patch
According to the HTTP specifications, only limited number of simultaneous connections are allowed, while loading pages. To increase that number, you can add the following entries to the Registry (they are not present by default):

HKEY_USERS.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Internet Settings
"MaxConnectionsPerServer"=dword:00000020
"MaxConnectionsPer1_0Server"=dword:00000020

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
"MaxConnectionsPerServer"=dword:00000020
"MaxConnectionsPer1_0Server"=dword:00000020

Note: Keep in mind that although those values work fine in most cases, they exceed the HTTP specifications and therefore might cause problems with some websites. If you experience problems, just remove the entries.