Windows 2000/XP Registry Tweaks Part-II

Read Part-I here

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.)

Note: Tcp1323Opts=”3″ might help in some cases where there is increased packet loss, however generally you’ll achieve better throughput with Tcp1323Opts=”1″, since Timestamps add 12 bytes to the header of each packet.

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)
[ Default is: 40 ]

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 specified in RFC 2018. SACK is especially 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 specified 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 specs), depending on the PPPoE software you use. Check the following location in the Registry:
HKLM\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols
ProtocolMTU=”1480″

Windows 2000 Web Patch:

According to the HTTP specs, 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:00000010
“MaxConnectionsPer1_0Server”=dword:00000010

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
“MaxConnectionsPerServer”=dword:00000010
“MaxConnectionsPer1_0Server”=dword:00000010

Special thanks to my friend Philip.

~ by culpritz on February 22, 2008.