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BuildOrBuy News
../images/bullet2.gifDialUp Networking
  1. ../images/bullet2.gif299357 - How to Reset Internet Protocol (TCP-IP) in Windows XP:
  2. ../images/bullet2.gifHome and Small Office Networking with Windows XP:
  3. ../images/bullet2.gifIntroduction to TCP-IP
Windows TCP/IP Tweak Settings:
Broadband Internet Connection optimization...

Having difficulties with Broadband throughput? Maybe Win2000 requires a little help? All of these parameter are set in the Registry. Travel @ your own risk. With that having been said, let's take a look! We have a few Tools to use which make this process less painful. As always, we are not responsible for your results if you mess up!

../images/bullet2.gifMTU (Maximum Transmission Unit) The largest packet size that can be transmitted over the network. Messages longer than the MTU value must be divided into smaller packets by the communications protocol (TCP/IP).

../images/bullet2.gifTCP-IP & NBT Configuration Parameters for Windows 2000-NT


Key: Adapter Name \Parameters\Tcpip

NOTE : In Windows 2000 and later this value is under the following key:
Key: Tcpip\Parameters\Interfaces\ ID for Adapter
Value Type: REG_DWORD Number
Valid Range: 68 - the MTU of the underlying network
Default: 0xFFFFFFFF
Description: This parameter overrides the default Maximum Transmission Unit (MTU) for a network interface. The MTU is the maximum packet size in bytes that the transport will transmit over the underlying network. The size includes the transport header. Note that an IP datagram may span multiple packets. Values larger than the default for the underlying network will result in the transport using the network default MTU. Values smaller than 68 will result in the tranport using an MTU of 68."

../images/bullet2.gifRWIN (Receive WINdow) A TCP/IP setting in Windows defining buffer size which holds incoming packets. RWIN is also set in the Registry as is MTU values.

If you'd like to take a closer peek to see the MTU & RWIN Registry values, call up regedit.exe, navigate to:
  • [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ Parameters]

You will see: TcpWindowSize

  • [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\ Parameters\Interfaces]

Now you'll need to determine which of these locations has your LAN Adapter to adjust the MTU value. No Can see?

RWIN & MTU are easier to set correctly from someone who's "Been There And Done That!"

This info may also prove helpful to those using IPSwitch, WS_FTP - Receive error blocking call canceled. MTU settings can also affect this application's behavior.


For those of us who just want to set these values and move on:

../images/bullet2.gif1.) - Select: RWIN - rwin2k-l.reg (Windows 2000 Registry File). 

IF you need help manually adjusting the RWIN value use this:


Use the command line ping.exe to determine optimal MTU Settings. Open a DOS Window. See Microsoft KB article Q159211 on using PING tool to determine MTU (see More Information Section). We found the following results for our use. Your results may vary. Check and tweak!

ping -f -n 10 -l 1472 host_or_IP


ping -f -n 10 -l 1472
ping -f -n 10 -l 1462
ping -f -n 10 -l 1464
ping -f -n 10 -l 1465 xxx Too much!
ping -f -n 10 -l 1464 - Just Right!

Once you know this MTU value, here's an application to use for setting this without fumbling around in the Registry. Click on MTU Tool Download. Follow the directions. 


Better alternative, use: DrTCP


Background Research:

Our magic MTU Number Value for Ethernet Broadband on Win2000 = 1500 (1472 or less for Broadband Ethernet use as shown above.) Test and tweak as needed.

Recommended Values

  • 576 - Dial-up Connections
  • 1492 - PPPoE Broadband Connections
  • 1500 - Ethernet, DSL and Cable Broadband Connections
  1. ../images/bullet2.gifSustainable Softworks - IPNetTuner for Windows: "IPNetTuner supports over 16 adjustable parameters including the TCP Window Size, Time Out intervals, Selective ACK (SACK) settings, and MTU. It also provides a convenient test tool so that you can immediately observe the results after adjusting specific parameters. The Link Rate tool is specifically designed to ensure that you are getting the throughput claimed by your ISP." (3/30/2003).
  2. How to Reset Internet Protocol (TCP/IP) in Windows XP: Core Component -

    "In extreme cases, reinstalling the Internet Protocol stack may be the most appropriate solution. With the NetShell utility, you can now reset the TCP/IP stack back to a pristine state, to the same state as when the operating system was installed."

  3. 301041 - HOW TO Install NetBEUI on Windows XP: Not supported but available if you insist on using!
  4. Windows 2000 Server TCP-IP Core Networking Guide Glossary
  5. Default MTU Size for Different Network Topology
  6. TCP-IP & NBT Configuration Parameters for Windows 2000-NT
  7. Table of Contents from Microsoft Windows 2000 TCP-IP Protocols and Services Technical Reference
  8. TCP-IP Routing Basics for Windows NT: The Route Table
  9.  Windows 2000 Tweaks
  10.  Windows Registry Guide - Change the Maximum Transmission Unit (MTU) Size (Windows NT-2000-XP)
  11. Dynamic Host Configuration Protocol (DHCP) for Microsoft Windows 2000
  12. Increasing TCP Receive Window for Microsoft Windows
  13. Cable Modems & xDSL Registry Tweaks
  14. Cable Modems & xDSL Speed Patches and Programs
  15. Windows MaxMTU Fix - InfiniSource, Inc.
  16. TweakMASTER - Rose City Software Collection - InfiniSource, Inc.
  17. MTU and MSS
  18. ; Internet
  19. WS_FTP - Receive error blocking call canceled: Bogus! Our Take - USE a different FTP application! 
  20. WS_FTP - Multiple PORT command errors: Our Take - USE a different FTP application! 
  21. WS_FTP - Changing the MTU setting to 576: "Blocking called Cancelled" errors on Win95/98.
  22. WS_FTP FAQs:
  23. WSPCancelBlockingCall: Platform SDK: Windows Sockets - TCP/IP programming from Microsoft.

Note: Our experience with Blocking called Cancelled" errors using WS_FTP after having communicated with Ipswitch Tech Support dictates getting a NEW FTP application! We recommend FTP Voyager, Award Winning FTP Client - Viola! Problem solved!

Browse Master
DNS Events
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../images/bullet2.gifChapter 1 - Introduction to Windows NT Routing with Routing and Remote Access Service


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Web Development, Gill Boyd & Team - Posted 01/18/2001; Updated 03/12/2009