How to Optimize Windows NT to Run Over Slow WAN Links w/TCP/IP

This article was previously published under Q140552
This article has been archived. It is offered "as is" and will no longer be updated.
In some customer situations, it may be necessary to change some Registryvalues when using TCP/IP across a Wide Area Network (WAN) that has slowlinks.

Optimizing Windows NT to Run Over Slow WAN Links with TCP/IP

All of the TCP/IP parameters are registry values located under one of twodifferent subkeys of:




<Adapter Name>\Parameters\Tcpip

where <Adapter Name> refers to the subkey for a network adapter to which TCP/IP is bound such as Lance01.

Values under the latter key(s) are specific to each adapter. You mustreboot the computer for a change in any of these parameters to takeeffect.

NOTE: The Windows NT 3.5 Resource Kit documentation was not updatedproperly from version 3.1. It lists a number of invalid TCP/IP registryparameters. The parameters listed in this Knowledge Base article should beused instead. The Windows NT 3.5 TCP/IP stack was completely rewritten, somany of the old parameters are no longer valid. The Windows NT3.51 Resource Kit should include the necessary corrections or refer to thewhitepaper available at the following location:
File Name: Tcpipimp2.doc
Location :
Title : "Microsoft Windows NT 3.5/3.51/4.0: TCP/IP Implementation Details TCP/IP Protocol Stack and Services, Version 2.0"

Step-by-Step Procedure

CAUTION: The Windows NT 3.5 TCP/IP implementation is largely self tuning.Adjusting registry parameters may adversely affect system performance.
  1. Increase TcpMaxConnectRetransmissionsTcpMaxConnectRetransmissions
    Key: Tcpip\Parameters
    Value Type: REG_DWORD - Number
    Valid Range: 0 - 0xFFFFFFFF
    Default: 3

    Description: This parameter determines the number of times TCP willretransmit a connect request (SYN) before aborting the attempt. Theretransmission timeout is doubled with each successive retransmission in agiven connect attempt. The initial timeout value is three seconds.

    Notice that the timeout value doubles after each transmission retry.Increasing the default value may allow a client to connect over a slowWAN.
    The value should only be changed in very small increments because behavioris governed by the value below. Too large a value could ensure that aconnection attempt will never time out.

    Key: Tcpip\Parameters
    Value Type: REG_DWORD - Number
    Valid Range: 0 - 0xFFFFFFFF
    Default: 5

    Description: This parameter controls the number of times TCP willretransmit an individual data segment (not connection request segments)before aborting the connection. The retransmission timeout is doubled witheach successive retransmission on a connection. It is reset when responsesresume. The base timeout value is dynamically determined by the measuredround-trip time on the connection.

  2. Increase TcpWindowSizeTcpWindowSize
    Key: Tcpip\Parameters
    Value Type: REG_DWORD - Number of bytes
    Valid Range: 0 - 0xFFFF
    Default: The smaller of 0xFFFF

    OR (The larger of four times the maximum TCP data size on the network
    8192 rounded up to an even multiple of the network TCP data size.)

    The default is 8760 for Ethernet.

    Description: This parameter determines the maximum TCP receive window sizeoffered by the system. The receive window specifies the number of bytes asender may transmit without receiving an acknowledgment. In general,largerreceive windows will improve performance over high delay, high bandwidthnetworks. For greatest efficiency, the receive window should be an evenmultiple of the TCP Maximum Segment Size (MSS).

    Reducing the TCP Window size effectively causes an acknowledgment to besent to the sender for data received sooner. This will lower thepossibility that the sender will time out while waiting for anacknowledgment. However it will also increase the amount of networktrafficand cause slower throughput.

  3. Reduce the ReplicationGovernor valueYou can add the ReplicationGovernor parameter to the registry of a backup domain controller (BDC) under:

    ReplicationGovernor REG_DWORD
    Range: 0 to 100 percent
    Default: 100
    This defines both the size of the data transferred on each call to the primary domain controller (PDC) and the frequency of those calls. For example, setting ReplicationGovernor to 50% will use a 64-KB buffer rather than a 128-KB buffer and will only have a replication call outstanding on the net a maximum of 50% of the time.

    Do not set ReplicationGovernor too low, or replication may never complete. A value of 0 will cause Netlogon to never replicate. The SAM/LSA database will be allowed to get completely out of synchronization.

    BDCs can be configured for the variances of WAN types. ReplicationGovernor allows the administrator to control the partial synchronization parameters. This parameter must be set individually on each BDC.

    NOTE: It is also possible to configure different replication rates at different times of the day using a script file with the AT command (for example, net stop netlogon, regini scriptfile, net start netlogon). The script file contains the path to the RegistrationGovernor parameter and the new Registry entries. Regini.exe is part of the Windows NT Resource Kit.

    This entry should only be changed if replication is being done across a slow WAN. Replication across a slow WAN link is network intensive and not recommended.

  4. Remove WINS and use lmhosts files instead for name resolution across link. This will cause NetBIOS name resolution to occur on the local machine or the local segment so that a connection to a WINS server across the WAN is not attempted.
  5. To reduce print browsing traffic, follow the suggestions in the following article in the Microsoft Knowledge Base:
    131902 Printer Browse Thread May Cause Extensive Network Traffic
For additional information about TCP/IP and NBT Configuration Parameters, please see the following article in the Microsoft Knowledge Base:
120642 TCP/IP and NBT Configuration Parameters for Windows 2000 or Windows NT

Article ID: 140552 - Last Review: 02/28/2014 07:59:33 - Revision: 2.1

Microsoft Windows NT Workstation 3.5, Microsoft Windows NT Workstation 3.51, Microsoft Windows NT Workstation 4.0 Developer Edition, Microsoft Windows NT Server 3.5, Microsoft Windows NT Server 3.51, Microsoft Windows NT Server 4.0 Standard Edition, Microsoft TCP/IP-32 for Windows for Workgroups 1.0

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