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TCP/IP settings for Broadband Internet connection in Windows XP

Topics on this page:

[1] TCP/IP

[2] Tools



TCP/IP is a big subject which cannot be covered in detail here. Only the settings that affect broadband internet access using cable or ADSL in Windows XP is described, based on the recommendation from speedguide.net, dslreports.com and Microsoft and this article does not cover the PPPoE protocol (see KB 283070).

Windows XP automatically detects your network and internet settings by default. Some people claim that Windows XP already manages the TCP/IP settings adequately without further tweaking.

I cannot verify whether tweaking has improved my connection. If the broadband bandwidth is 1Mbs or above (as in my own case, with speed as high as >10Mbs peak) it will probably not make a lot of difference for browsing most websites. There are other factors involved such as routers, internet traffic and servers. There are some websites (forums) which I access with great difficulty whereas others are very quick.

However, there seems to be no harm following the experts' guide and set the recommended TCP/IP parameters in the registry manually or with tools, provided you know what you're doing and you make a backup of the registry or system restore point beforehand. Some tweaks on the internet merely reproduces or slightly modifies what Windows XP have by default so don't fool yourself into believing that it works some magic.

If you're not sure, leave it alone. I would NOT spend any money on any tools which claim to increase internet speed. Without manual tweaking, some parameters in the registry are not set by default so you have to add them yourself.


2. Tools

You can use TCPOptimizer and DrTCP which you'll find on the above websites. They are similar in function although the former has more options. TweakXP also has an option to optimise internet connection but I don't know what it changes; therefore I would use the other tools.

You should first check your MaxMTU value by pinging some websites; this you can do in TCPOptimizer in the Latency (PING) tab. Or you can use the ping command in the command prompt in Windows. A value of 1500 is the maximum you can set and is normally suitable.

The default TTL can be set to 128 (default in Windows XP) or 64 (recommended by SpeedGuide); normally it won't make any difference.

The TCP Receive Window has a maximum value of 256960 or an even divisible of it, or calculated according to the above websites' guides. It should be an even multiple of the TCP Maximum Segment Size (MSS) as determined by MTU. The other settings are shown in fig. 1.

Fig. 1. TCP Optimizer settings


After you click Apply changes you would be prompted to reboot the computer to take effect.

The corresponding registry settings are (all DWORD values in decimal):


TcpWindowSize = 256960 [=44*(1500-40)*2*2]
EnablePMTUDiscovery = 0 or 1 [0=defaults to 576 bytes]
EnablePMTUBHDetect = 0 [Black Hole detect =false]
SackOpts = 1 [enabled for large TCP window sizes]
TcpMaxDupAcks = 2 [Max Duplicate ACKs]
DefaultTTL = 64 (or 128)
Tcp1323 Opts =  1 [Window Scaling enabled for large TCP window support; other values: 0 (none);2 (Timestamps only); 3 (both)]

The key for the MTU is located elsewhere:

Parameters\Interfaces\{ID for Network Adaptor}

MTU = 1500 [range 68-1500]

The network adaptor ID would be different in your case. This setting overrides the maximum MTU for the network adaptor and potentially conflicts with the EnablePMTUDiscovery setting if set to 1 (see the references for more).

As to what these terms mean, consult the references below and other network references.


TCP/IP and NBT Configuration Parameters for Windows XP

Speedguide.net Windows 2000/XP Registry Tweaks


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Copyright 2003 by Kilian. All my articles including graphics are provided "as is" without warranties of any kind. I hereby disclaim all warranties with regard to the information provided. In no event shall I be liable for any damage of any kind whatsoever resulting from the information. The articles are provided in good faith and after some degree of verification but they may contain technical or typographical errors. Links to other web resources may be changed at any time and are beyond the control of the author. Articles may be added, removed, edited or improved at any time. No support is provided by the author.

This is not an official support page for any products mentioned. All the products mentioned are trademarks of their companies. Edit the registry at your own risk and back up first.

Last updated 28 Nov 2004