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Outlook Anywhere is ‘broken’ on IPv6 in Windows Server 2008

Posted by Steven Bink July 2, 2008 11:59 AM with 1 comment(s)

Filed under: Exchange

Kevin Reeuwijk: I run Exchange 2007 SP1 on Windows Server 2008 RC1 and have run different beta’s of both products for some time now. In every case, I ran into the following problem: Outlook Anywhere (aka RPC over HTTP) would not work if the RPC-over-HTTP Proxy and the Exchange mailbox were on the same Windows 2008 server. Outlook would fail to connect to the server over the internet with some generic error message. When I was running the same configuration on a Windows 2003 server however, the problem did not occur. Also, if I put the RPC-over-HTTP Proxy on a seperate Windows 2003 server and the mailbox on a Exchange 2007 SP1 on Windows 2008 server, Outlook Anywhere worked just fine. I always thought it was a bug in either Exchange or Windows 2008, but I became convinced the problem was more serious when I still had problems with the official Exchange 2007 SP1 release on Windows 2008 RC1…

Meanwhile, I had already accepted the fact that I had to run the RPC-over-HTTP Proxy on a Windows 2003 machine for now, so that was how my environment was set up. However, when troubleshooting a different problem with Exchange, I stumbled upon the rootcause of the Outlook Anywhere problem! It turns out that the problem is in IPv6 and the way that Windows 2008 (and Vista btw) handles IPv6 as a preferred protocol over IPv4: When I did a “netstat -a -n” on my Windows 2008 machine, I noticed that Exchange was listening on the usual ports 6001, 6002 and 6004 on its IPv4 address, but only on ports 6001 and 6002 on its IPv6 address. The DSProxy service (port 6004) is NOT listening on the IPv6 stack!!! This now explains the behaviour that I was experiencing:

Because Windows 2008 prefers IPv6 over IPv4, it talks to itself over IPv6. So when the RPC-over-HTTP Proxy tries to connect a user session to port 6004 on the same server, it tries to connect to :::1:6004 and NOT to 127.0.0.1:6004. Because the server is not listening to port 6004 on the IPv6 stack, the connection fails.
If you put the RPC-over-HTTP proxy on a Windows 2003 server, the problem disappears because the Windows 2003 server only uses IPv4 to talk to Exchange on the Windows 2008 server.

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Microsoft will put this on the QFE list for SP2…

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Comments

cchance said:

kinda funny that this would happen but kinda to be expected, ipv6 is a huge undertaking, but what makes it worse is since its not really in practical full scale use yet its not really tested so now that 2008 is starting to push it to the default it's bound to show up problems eventually.

July 6, 2008 7:03 AM

About Steven Bink

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