XCON: 9156 Errors Occur after Applying Exchange 5.5 Service Pack 2

ID: Q229643

The information in this article applies to:

Microsoft Exchange Server, version 5.5

SYMPTOMS

After you apply Service Pack 2 for Exchange Server 5.5, the following error messages may be found in the Event Viewer application log:

Event ID: 9156
Source: MSExchangeMTA
Type: Warning
Category: Resource
Description: A resource limit has been reached while attempting to open an association. There are no free control blocks available for network type 1. The configured count is 40. [BASE IL MAIN BASE 1 282] (10)

After you receive this error message, the message transfer agent (MTA) may stop processing messages and require a restart of the service to get mail flowing again.

CAUSE

The MTA leaks control blocks. Under stress, or slow link conditions, this problem becomes apparent.

RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next Microsoft Exchange Server version 5.5 service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

The English version of this fix should have the following file attributes or later:

Component: Message Transfer Agent

File name	Version
Dbserver.sch	N/A
Dcprods.cat	N/A
Ems_rid.dll	5.5.2590.0
Emsmta.exe	5.5.2590.0
Info4log.cfg	N/A
Infoblog.cfg	N/A
Infodlog.cfg	N/A
Infollog.cfg	N/A
Infoplog.cfg	N/A
Infotlog.cfg	N/A
Mtacheck.exe	5.5.2590.0
Mtamsg.dll	5.5.2590.0
P2.xv2	N/A
X400om.dll	5.5.2590.0
X400omv1.dll	5.5.2590.0

NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:

Q154871 Determining If You Are Eligible for No-Charge Technical Support

STATUS

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.5.

MORE INFORMATION

The MTA uses one control block (CB) for each association (whether remotely or locally initiated). It also uses one CB to listen for incoming associations.

The problem occurs when an association is active and waiting for a response to a Turn-Please Request, and the remote side sends an association recovery inbound. Because the association is still active, recovery handling does not work properly, and the upper layer CBs for the association are released (and eventually reused by other associations) while the lower layers remain unaware of this fact.

Later, the lower layers get closed down and POP-4 sends a Close Request up to the Platform Kernel CB, which is now used by some other association. The Close Request is ignored so no Close Response is sent back and so the POP-4 CB is not closed down properly (or leaked).

Much later on, an Open Request comes down from Platform from a Kernel CB, which matches the old partner of the leaked POP-4 CB. This causes the Open Request to be ignored by POP-4 as a Duplicate Open. The Open Request then gets passed on to the Winsock layer by the Base Open handling and is logged as a 9156 error. For more information, please see the following articles in the Microsoft Knowledge Base:

Q193894 XCON: MTA Stops Processing Messages and Generates 9156 Events

Q166602 XCON: MTA Only Allows 64 TCP/IP or TP4 Connections

Additional query words: 9156 restart mta exchange bridgehead slow link


Keywords          : 
Version           : winnt:5.5
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: July 7, 1999