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Disabling TCP/IP Nagle Algorithm Improves Speed on Slow Nets

This article was previously published under Q138831
SYMPTOMS
This article explains the Nagle TCP/IP algorithm and how to manuallydisable it on different the SNA Server client and server releases fordifferent operating systems. It also mentions how to obtain an update thatautomatically disables this algorithm.Microsoft has updated the file <snaroot>\SYSTEM\SNAIP.DLL to correct thisproblem.
STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.
This correction is included in the latest U.S. Service Pack for SNA Server for Windows NT, version 2.11. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):
S E R V P A C K
MORE INFORMATION

The Nagle TCP/IP Algorithm

The Nagle TCP/IP algorithm was designed to avoid problems with smallpackets, called tinygrams, on slow networks. The algorithm says that aTCP/IP connection can have only one outstanding small segment that has notyet been acknowledged. The definition of "small" varies but usually it isdefined as "less than the segment size" which on ethernet is about 1500bytes.

Manually Disabling the Nagle Algorithm

You can disable the Nagle algorithm by performing the SNA Server client andserver modifications mentioned below and following the instructions in theActivating the Modifications section.

SNA Server Modifications

  1. Under the subtree HKEY_LOCAL_MACHINE add the subkey SNATCP under the following key:
    SYSTEM\CurrentControlSet\Services\Snabase\Parameters\ 					
  2. Choose Add Key from the Edit menu and use the following information:
          Value Name: NoDelay      Data Type:  REG_SZ      String:     yes					

Windows 95 SNA Client Modifications

Add the same registry entry as SNA Server above.

Windows 3.x Modifications

Windows 3.x client always disables the Nagle algorithm and there is no wayto enable it.

Activating the Modifications

When the NoDelay is set to yes, the TCP/IP transport DLL uses theTCP_NODELAY option when it opens a socket.

For this to take effect, the client server interface must be stopped andrestarted on both the server and client after the registry changes havebeen made. The following table shows the name of the SNA client serverinterface program and the corresponding operating system platform:
   Client Server Interface      Platform   ----------------------------------------   SNABASE Service              Windows NT   SNABASE Service              Windows 95   WNAP.EXE                     Windows 3.x				
Note: The Nagle algorithm is defined in TCP/IP RFC 896.
prodsna 2.10 2.11
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Article ID: 138831 - Last Review: 11/19/2003 13:54:00 - Revision: 2.0

  • Microsoft SNA Server 2.1
  • Microsoft SNA Server 3.0
  • kbbug kbfix KB138831
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