I installed CAS server and it is throwing below errors continuously and some times active directory topology generator service is not starting. Process MSEXCHANGEADTOPOLOGYSERVICE.EXE (PID=1420). Topology discovery failed, error 0x80040a02 (DSC_E_NO_SUITABLE_CDC). Look up the Lightweight Directory Access Protocol (LDAP) error code specified in the event description. To do this, use Microsoft Knowledge Base article 218185, "Microsoft LDAP Error Codes." Use the information in that article to learn more about the cause and resolution to this error. Use the Ping or PathPing command-line tools to test network connectivity to local domain controllers. Few blogs and articles suggested to add the Exchange server computer account to domain admins group and it fixed problem for most of guys. But I can not do that like a blind man and I want to understand the reason for it. Any one around here to help me what is going wrong?Thanks, Sitaram www.sitaram-pamarthi.com

I'd suggest you verify its presence in the Exchange Domain Servers Group. It should not be in the domain admins group. Also, I've seen a post that prevents the installation of the CAS role if IPv6 is disabled. Is yours?finally, since its topology we're talking about, do you have any Windows 2000 domain controllers in the same AD site? Do you have a global catalog in the same AD site? Is the Exchange server pointed to the correct DNS server?Please open event viewer and post the complete error here. Mike Crowley A+, Network+, Security+, MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator

HI, Did you tried to install CAS server on Windows 2008 ?This issues may be happen when you didnt' disable IPv6 permanently. SO please fallow below procedure and re-install your CAS server.To completely disable IPv6 on a Windows Server 2008-based computer yourself, follow these steps: 1. Open Registry Editor. 2. Locate the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters 3. In the details pane, click New, and then click DWORD (32-bit) Value. 4. Type DisabledComponents, and then press ENTER. 5. Double-click DisabledComponents, and then type 0xffffffff in Hexadecimal or 4294967295 in Decimal.Note The 0xffffffff value or the 4294967295 value disables all IPv6 components except for the IPv6 loopback interface NOTE-: BEFORE DO ANY CHANGES IN REGISTREY PLEASE DO THE REGISTRY BACKUP.Regards Chinthaka

Hi, The server's computer account should be a member of "Exchange Servers" and/or domain local "Exchange Install Domain Servers" security groups. Note that the "Exchange Servers" group is an universal group that is by default created in root domain when setup /prepare switches are run. Permission Considerations http://technet.microsoft.com/en-us/library/aa996881.aspx Besides please try to use DCdiag to check if any DC connectivity issue has occurred there. Please check if you have Windows Firewall and IPSec Policy Agent service running. If that is not the issue, then please feel free to post all the detail error event information here for further troubleshooting. Regards, Xiu

>Also, I've seen a post that prevents the installation of the CAS role if IPv6 is disabled. Is yours?Not mine>finally, since its topology we're talking about, do you have any Windows 2000 domain controllers in the same AD site? Yes, I have Windows 2003 DC>Do you have a global catalog in the same AD site? Yes>Is the Exchange server pointed to the correct DNS server? Yes>Please open event viewer and post the complete error here. Event Event Type: ErrorEvent Source: MSExchange ADAccessEvent Category: Topology Event ID: 2114Date: 7/7/2009Time: 7:11:24 PMUser: N/AComputer: MAILCAS1Description:Process MSEXCHANGEADTOPOLOGYSERVICE.EXE (PID=1340). Topology discovery failed, error 0x80040a02 (DSC_E_NO_SUITABLE_CDC). Look up the Lightweight Directory Access Protocol (LDAP) error code specified in the event description. To do this, use Microsoft Knowledge Base article 218185, "Microsoft LDAP Error Codes." Use the information in that article to learn more about the cause and resolution to this error. Use the Ping or PathPing command-line tools to test network connectivity to local domain controllers.For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.Tail of installation log [6/26/2009 10:12:18 PM] [2] Service 'MSExchangeADTopology' failed to reach status 'Running' on this server after waiting for '30000' milliseconds.[6/26/2009 10:12:18 PM] [2] The remaining time for service status change is '00:14:30'.[6/26/2009 10:12:18 PM] [2] Service checkpoint has progressed. Previous checkpoint='1' - Current checkpoint='2'.[6/26/2009 10:12:18 PM] [2] Will wait '650000' milliseconds for the service 'MSExchangeADTopology' to reach status 'Running'.[6/26/2009 10:23:08 PM] [2] Service 'MSExchangeADTopology' failed to reach status 'Running' on this server after waiting for '650000' milliseconds.[6/26/2009 10:23:08 PM] [2] The remaining time for service status change is '00:03:40'.[6/26/2009 10:23:08 PM] [2] Service 'MSExchangeADTopology' failed to start. Check the event log for possible reasons for the service start failure.[6/26/2009 10:23:08 PM] [2] [ERROR] Unexpected Error[6/26/2009 10:23:08 PM] [2] [ERROR] Service 'MSExchangeADTopology' failed to start. Check the event log for possible reasons for the service start failure.[6/26/2009 10:23:08 PM] [2] Ending processing.[6/26/2009 10:23:08 PM] [1] The following 1 error(s) occurred during task execution:[6/26/2009 10:23:08 PM] [1] 0. ErrorRecord: Service 'MSExchangeADTopology' failed to start. Check the event log for possible reasons for the service start failure.[6/26/2009 10:23:08 PM] [1] 0. ErrorRecord: Microsoft.Exchange.Configuration.Tasks.ServiceFailedToStartException: Service 'MSExchangeADTopology' failed to start. Check the event log for possible reasons for the service start failure.[6/26/2009 10:23:08 PM] [1] [ERROR] Service 'MSExchangeADTopology' failed to start. Check the event log for possible reasons for the service start failure.[6/26/2009 10:23:08 PM] [1] Setup is halting task execution because of one or more errors in a critical task.[6/26/2009 10:23:08 PM] [1] Finished executing component tasks.[6/26/2009 10:23:08 PM] [1] Ending processing.[6/26/2009 11:01:11 PM] [0] [WARNING] Setup has made changes to operating system settings that require a reboot to take effect. Please reboot this server prior to placing it into production.[6/26/2009 11:01:14 PM] [0] End of Setup Thanks, Sitaram www.sitaram-pamarthi.com

>Did you tried to install CAS server on Windows 2008 ? No..I am not trying to Install on Windows 2008..I did it on windows 2003 box Thanks, Sitaram www.sitaram-pamarthi.com

The cas server was not added to any of the security groups after installation. I can try adding them to exchange related groups but I want to understand the reason and do it later if there no other go. DCdiag output is very clean.Thanks, Sitaram www.sitaram-pamarthi.com

There might be "N" number of reasons to say why topology service is failing. But my issue got fixed in this way. I have a duplicate account with same name in root domain; I deleted that Tried restarting the CAS server -- no luck Uninstalled CAS role Installed it again This time it worked Solutions may vary from persons to person and the above worked for me as it is a environmental issue Thanks, Sitaram www.sitaram-pamarthi.com