In some customer situations, it may be necessary to change some Registry
values when using TCP/IP across a Wide Area Network (WAN) that has slow
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 two
different subkeys of:
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 must
reboot the computer for a change in any of these parameters to take
NOTE: The Windows NT 3.5 Resource Kit documentation was not updated
properly from version 3.1. It lists a number of invalid TCP/IP registry
parameters. The parameters listed in this Knowledge Base article should be
used instead. The Windows NT 3.5 TCP/IP stack was completely rewritten, so
many of the old parameters are no longer valid. The Windows NT
3.51 Resource Kit should include the necessary corrections or refer to the
whitepaper available at the following location:
CAUTION: The Windows NT 3.5 TCP/IP implementation is largely self tuning.
Adjusting registry parameters may adversely affect system performance.
- Increase TcpMaxConnectRetransmissions
Value Type: REG_DWORD - Number
Valid Range: 0 - 0xFFFFFFFF
Description: This parameter determines the number of times TCP will
retransmit a connect request (SYN) before aborting the attempt. The
retransmission timeout is doubled with each successive retransmission in a
given 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 slow
The value should only be changed in very small increments because behavior
is governed by the value below. Too large a value could ensure that a
connection attempt will never time out.
Value Type: REG_DWORD - Number
Valid Range: 0 - 0xFFFFFFFF
Description: This parameter controls the number of times TCP will
retransmit an individual data segment (not connection request segments)
before aborting the connection. The retransmission timeout is doubled with
each successive retransmission on a connection. It is reset when responses
resume. The base timeout value is dynamically determined by the measured
round-trip time on the connection.
- Increase TcpWindowSize
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 size
offered by the system. The receive window specifies the number of bytes a
sender may transmit without receiving an acknowledgment. In general,
receive windows will improve performance over high delay, high bandwidth
networks. For greatest efficiency, the receive window should be an even
multiple of the TCP Maximum Segment Size (MSS).
Reducing the TCP Window size effectively causes an acknowledgment to be
sent to the sender for data received sooner. This will lower the
possibility that the sender will time out while waiting for an
acknowledgment. However it will also increase the amount of network
and cause slower throughput.
- Reduce the ReplicationGovernor value
You can add the ReplicationGovernor parameter to the registry of a backup domain controller (BDC) under:
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.
Range: 0 to 100 percent
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.
- 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.
- To reduce print browsing traffic, follow the suggestions in the
following article in the Microsoft Knowledge Base:
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:
TCP/IP and NBT Configuration Parameters for Windows 2000 or Windows NT
Article ID: 140552 - Last Review: February 28, 2014 - 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
|kbnosurvey kbarchive kbnetwork KB140552|