Troubleshooter: Retiring GC Servers

We want to retire several Global Catalog (GC) servers and retask them as domain controllers (DCs). What will happen if these GCs suddenly disappear?

GC servers contain a partial copy of the attributes for every object in an Active Directory (AD) forest, not just objects for the server domain. As a result, GC servers can answer Lightweight Directory Access Protocol (LDAP) queries from any Exchange server in the forest by listening on TCP port 3268. Newly created GCs receive DNS SRV records that register their existence and let Exchange find them. Demoting a GC server removes the SRV record and turns off the listener, but the code that tells Outlook clients where to make directory queries doesn't reflect the server disappearance, so Outlook 2000 and earlier clients might stop responding. To fix this problem, perform the following steps:

  1. A week before you demote the servers, you must set the RFR Target Server registry value of type REG_MULTI_SZ under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeSA\Parameters registry subkey. RFR Target Server should contain the names of all GC servers that you aren't demoting (For more information about this process, see the Microsoft article "XCCC: DSProxy Configuration for Static Ports on Exchange Cluster" at
  2. Demote the target server, preferably during off hours when few (or no) clients will be using it.
  3. Use the Dsadiag tool to verify that the demoted computer doesn't continue to show up as a GC server. If it does, manually remove the SRV record, then run
  4. ipconfig /flushdns

    on every Exchange 2000 Server machine.

  5. Reboot the target server to reset the Name Service Provider Interface (NSPI) on the former GC server; the NSPI will continue to run and disrupt Messaging API (MAPI) client name resolution until after you restart the GC server.
  6. Relaunch any Outlook 2000 and earlier clients; otherwise, they won't notice that the former GC server is no longer a GC.
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