Microsoft KB Archive/946091

= An audio or video session exits unexpectedly when an external user tries to add a third user to the session in Communications Server 2007 =

Article ID: 946091

Article Last Modified on 1/4/2008

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APPLIES TO


 * Microsoft Office Communications Server 2007 Enterprise Edition

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SYMPTOMS
In an environment that is running Microsoft Office Communications Server 2007, an external user can establish an audio or video session with a user who is connected to the internal network as expected. However, when an external user tries to add a third user to the audio or video session, the session exits unexpectedly.

Additionally, if you create and then examine the Communicator-uccp.log file, you notice that Communications Server 2007 generated a &quot;500 Server&quot; error.

Note The Communicator-uccp.log file is located in the %USERPROFILE%\tracing folder.

This issue occurs in an environment that has the following configuration:
 * You have a Consolidated Office Communications Server 2007 Enterprise Edition pool that is deployed behind a hardware load balancer device.
 * The hardware load balancer device is running in a destination network address translation (DNAT) configuration.



WORKAROUND
To work around this issue, use one of the following methods.

Method 1: Add an entry in the hosts file
Modify the hosts file on each front-end server in the Communications Server 2007 pool. In the hosts file, add an entry to map the fully qualified domain name (FQDN) of the pool to the IP address that is assigned to the particular front-end server.

Note You must perform this action on each front-end server.

Method 2: Change the load balancer configuration to use SNAT
Change the load balancer configuration to use source network address translation (SNAT).

Note After you configure the network and the load balancer to use SNAT mode, you must change the pool settings to use the new configuration.

To change a pool to a SNAT configuration, follow these steps:  Log on to a front-end server. Click Start, click Run, type wbemtest, and then click OK. In the Windows Management Instrumentation Tester dialog box, click Connect. In the namespace box that appears in the upper-left area of the Connect dialog box, change the root\default entry to root\cimv2, and then click Connect. Click Enum Classes, click Recursive, and then click OK. Locate the MSFT_SIPPoolConfigSetting entry, double-click MSFT_SIPPoolConfigSetting, and then click Instances.

This action displays one instance for each pool that is configured in the forest. You must select the correct instance based on the back-end server of the pool that you want to modify. The back-end server is listed in the instance title as follows:

MSFT_SIPPoolConfigSetting.Backend=&quot; &quot;

 Double-click the correct instance based on the appropriate back-end server.</li> Locate the DNATMode entry, and then double-click DNATMode.</li> Change the TRUE value to FALSE, and then click Save Property.</li> Click Save Object, and then click Close three times.</li> Click Exit.</li> Allow for sufficient time to let the Active Directory directory service replicate the changes to the other domain controllers in the environment.</li> Restart the Front End service on each pool server.</li> After the Front End services are restarted, run the Front End Validation Wizard.</li> In this wizard, examine the Check DNAT settings for Pool section. The following information should be displayed:

Pool support for DNAT mode: Disabled

If pool support for DNAT is enabled, replication has probably not been completed successfully. In this scenario, wait for approximately 30 minutes, and then repeat steps 13 through 15.

If pool support for DNAT remains enabled after you repeat steps 13 through 15, repeat steps 1 through 15 to verify that the correct pool is selected.

Note If the changes that you configured in steps 1 through 15 reverted to the original value, make sure that you click Save Property in step 9 and Save Object in step 10.</li> After pool support for DNAT displays a value of Disabled, run the Front End Validation Wizard on every other front-end server in the pool.</li> Verify that the load balancer is configured to use SNAT mode.</li></ol>

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Trace information
When this issue occurs, trace information that resembles the following trace information is generated:

<pre class="fixed_text">SIP/2.0 500 The server encountered an unexpected internal error ms-user-logon-data: RemoteUser Authentication-Info: NTLM rspauth=&quot;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX&quot;, srand=&quot;XXXXXXXX&quot;, snum=&quot;XX&quot;, opaque=&quot;XXXXXXXX&quot;, qop=&quot;auth&quot;, targetname=&quot;OCS.WingTipToys.com&quot;, realm=&quot;SIP Communications Service&quot; From: &quot;Haas, Jonathan&quot;<sip:jonathanhaas@wingtiptoys.com>;tag=25ec93fdb9;epid=dbdeae581b To: <sip:kimakers@wingtiptoys.com;gruu;opaque=app:conf:audio-video:id:361F46DACC98CB4C82B67D960EDFCBC5>;tag=4379A86AAA4786CDE7C8CB9D65F9EC35 Call-ID: c111ff019ddc4632847b6f927dfe1c52 CSeq: 1 INVITE Via: SIP/2.0/TLS 10.10.20.22:51201;received=192.168.50.6;ms-received-port=29329;ms-received-cid=894CB700 ms-diagnostics: 3080;reason=&quot;Internal Error: AddUser failed&quot;;source=&quot;OCS.WingTipToys.com&quot; Content-Length: 0

Additional query words: OCS OCS2007

Keywords: kberrmsg kbtshoot kbprb KB946091

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