Hi We are running Exchange 2003 SP2 servers in a Windows 2003 AD forest.In our main site, we have Exchange servers located and also a group of DC's (that are also GC's).From what I understand, each Exchange server connects to a GC in the site that it is located in. It needs this for directory information.Couple of questions - i) How is this DC picked? Is it a random selection via SRV records when Exchange boots up?ii) If this DC is taking down (reboot etc), how does Exchange pick another one? Is there any form of outage?iii) Outlook clients also need to reference a GC. Is Exchange responsible for picking which GC Outlook clients reference? iv) Is the GC Outlook clients reference the same as the one Exchange is connected to, or are they balanced across?v) Is there any way to check which GC Exchange is currently connected to, or was at a certain time?The reason I ask is because we rebooted a GC last night, and the following alert is in the Event Log of an Exchange server:NSPI Proxy failed to connect to Global Catalog GC1.domain.com over transport Rpc/HTTP. This server is down or unreachable. Clients will not be directed to this GC until it is available again. Any help appreciated.Thanks

All your Answer in below reference. Exchange uses DSACCESS in order to cache the LDAP queries which it uses to communicate with GC and DC. Read the below article and you will get answer to all your queries. http://www.msexchange.org/tutorials/Closer-Look-Directory-Service-Access-DSAccess-Part1.html http://www.msexchange.org/tutorials/Closer-Look-Directory-Service-Access-DSAccess-Part2.html Vinod |CCNA|MCSE 2003 +Messaging|MCTS|ITIL V3|

Hi,Regardng the Question 1,2, I think the articles provided by Vinod have answered the questions. iii) Outlook clients also need to reference a GC. Is Exchange responsible for picking which GC Outlook clients reference?I would like to explain that since Outlook 2002, Outlook connect to DSPROXY service (Referral component)on Exchange to obtain a GC server for connecting. The DSProxy obtian the GC from the GC list which maintained by the DSAccessiv) Is the GC Outlook clients reference the same as the one Exchange is connected to, or are they balanced across?No, the GC server which Outlook uses is not same the as the one Exchange server is connected to. v) Is there any way to check which GC Exchange is currently connected to, or was at a certain time?It is hard to check which GC Exchange is currently connected to. You need to capture network package to check it. Nevertheless, for test purpose, you can hard-code the DC/GC server used by Exchange Server.Mike

HiA question relating to the Outlook connection to a GC.Ok, so I get that - via DSAccess - Exchange connects to various DC/GC's to function. At the same time, Outlook needs to connect to a GC for directory information.From what you are saying, Outlook connects to Exchange and Exchange provides a GC to Outlook using the DSProxy service?But what happens if Exchange and Outlook are in two different sites, and the two sites have their own GC's? Surely, the GC's that Exchange refers to Outlook via DSProxy will be residing in the same site as Exchange - which is not necessarily the same site as Outlook? Surely, Outlook should connect to a local GC, not one that is local to Exchange?Hope this makes sense and thanks for answering my question :)

Hi, Would you please let me know whether the Outlook connects to Exchange directly (connect two sites by using VPN) or through RPC over Http? If the Outlook connects to Exchange Server through RPC over HTTP, Outlook does not connect directly to global catalog servers by default. Instead, the users mailbox server forwards directory RPC requests to the global catalog servers. For your reference: RPC over HTTP Interactions on the Back-End Servers http://technet.microsoft.com/en-us/library/aa998383(EXCHG.65).aspx If the Outlook connects to Exchange Server directly through VPN, I suggest you read following articles regarding how DSProxy Referral component provide GC server to Outlook: Exchange 2003 post SP2 DSProxy Referral Update http://msexchangeteam.com/archive/2006/03/17/422350.aspx Exchange Server 2003 Service Pack 2 DSProxy Referral Process Changes http://msexchangeteam.com/archive/2005/11/04/413669.aspx Mike