Outlook Anywhere: RPC_S_SERVER_UNAVAILABLE error (0×6ba) was thrown by the RPC Runtime

When I set up Outlook Anywhere on Exchange 2007 and Windows 2008 I used the official MS tool (which I have to admit is actually pretty good)  www.testexchangeconnectivity.com . I kept getting this error:

Attempting to ping RPC Endpoint 6004 (NSPI Proxy Server)
RPC_S_SERVER_UNAVAILABLE error (0×6ba) was thrown by the RPC Runtime

After 2 days of endless head-scratching I  could isolate the problem. This is what I found out:

  • This can only happen on a system where all the Exchange Servers are on the same server, Client Access, Hub transport and Mailbox server.
  • It happens because Windows uses by default IPv6. You can disable it for your ethernet interfaces but Windows does not give you any control over the loopback interface.When all the Exchange servers are on the same machine, windows uses the loopback interface to intreact with the Client Access server. Thus it uses IPv6 which for some reason unknown to humanity, does not work.

Solution

The solution is suprisingly simple. Just open your hosts file and comment out both localhost sections (both the IPv4 one and the IPv6, ::1) . Now write the servers (local) IP address and (local) hostname and FQDN like this.

Note: It was pointed out to me in the comments that you don’t have to comment out the localhost lines. I wrote this a few months back and I don’t remember why I commented it out. The system is in a production environment and I don’t want to mess with it now.

#127.0.0.1     localhost
#::1           localhost
10.1.1.2       mailserver
10.1.1.2       mailserver.domain.local

Hope this saves somebody a headache.

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Comments (11)

  1. Skyline34 wrote::

    started out installing Exchange patch 8 for SP1 and it fixed the IPv6 problem for port 6004 but i was still getting an error when running the http://www.testexchangeconnectivity.com.
    Altered the hosts file as you suggested and its working perfectly!

    Thanks!

    Thursday, July 2, 2009 at 13:26 #
  2. Vinay wrote::

    Great find! Thanks you

    Friday, August 28, 2009 at 16:42 #
  3. Mike wrote::

    This had me stumped. Thanks!

    Friday, October 2, 2009 at 7:31 #
  4. Ryan wrote::

    This hosts file modification resolved my issue. All autodiscover tests now pass correctly.

    Wednesday, October 14, 2009 at 20:35 #
  5. Terry wrote::

    Thanks… was banging my head on the desk for 5 hours before finding this, fixed it for me!

    Tuesday, October 20, 2009 at 20:53 #
  6. Drew wrote::

    Thank you for posting this, it was quite helpful :-)

    Monday, November 2, 2009 at 16:24 #
  7. Fredrik wrote::

    Great info!
    But you dont need to comment out the localhost-rows.

    Just add one row with the server netbios and fqdn, example:
    —–
    10.1.1.2 mailserver mailserver.domain.local
    —–

    Tuesday, November 3, 2009 at 21:33 #
  8. asif wrote::

    Thank you bro…i was struggling with this issue since last 3 days. God Bless you.

    Saturday, November 7, 2009 at 19:30 #
  9. stripe wrote::

    You deserve a gold medal!!! You saved me a lot of grief…meaning a call to Microsoft…where some dude was going to take me for a troubleshooting roller coaster ride…

    Much love keep up the great work!

    Wednesday, February 3, 2010 at 19:30 #
  10. mbergman@brunson.us wrote::

    Dude I wish I found you 3 weeks ago! Thank you so much for this post. I wish I could buy you a case of your favorite brew.

    Saturday, March 6, 2010 at 23:31 #
  11. benni wrote::

    You are free to muy me a case of it :-)

    Sunday, March 7, 2010 at 23:03 #