Outlook Anywhere is ‘broken’ on IPv6 in Windows Server 2008
Posted by Kevin Reeuwijk in ExchangeI 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.
So while this may not be a huge problem right now, it will be in the future for:
- Native Windows 2008 environments where all Exchange servers are Windows 2008 and the RPC-over-HTTP proxy is on either one of the Exchange servers or on a seperate Windows 2008 server.
- Single server deployments (e.g. Small Business Server) where everything is condensed to a single Windows 2008 server.
The next step is: how to solve the problem in the meanwhile? Fortunately I found a workaround, although it might not be what you expect! The workaround is to disable IPv6 (duh!), however this proves rather difficult for Windows 2008 (and Vista): you can’t fully disable IPv6 in these products!
- If you’re in a multi-server scenario where the RPC-over-HTTP Proxy is not on the same server as Exchange 2007, than you can simply unselect IPv6 from the properties of your NIC (on the RPC-over-HTTP Proxy machine); that will force the RPC-over-HTTP Proxy to use IPv4 to talk to Exchange and everything will be fine.
- If you’re in a single-server scenario than you can’t disable IPv6 because whatever you do (including the “DisabledComponents” registry setting to disable even more IPv6 components), the loopback interface still uses IPv6.
So it seems that in the latter case, you’re screwed… Not so, because we fortunately still have good old ‘name resolution’ to help us out. Simply open up your hosts file and make the following changes:
- Comment out the line “:::1 localhost”
- Add the following two lines:
<IPv4 address> <hostname of the computer>
<IPv4 address> <FQDN of the computer>
This will resolve all queries for your computer’s name to its IPv4 address, effectively disabling the use of IPv6 for self-communication. You can confirm that this works by doing a “telnet localhost 6004″.
I will pass this issue on to Microsoft when I attend the Exchange ’14′ Summit next week, so hopefully they can fix it soon.
Kevin Reeuwijk
UPDATE: Microsoft has told me that they will put this on the QFE list for SP2…
. Compared to Vista I have found only 3 features missing:
I got Windows Server 2008 Beta 3 running natively on my Dell laptop! Based on my experience so far, I like this OS even more than Windows Vista! It’s stable, fast and fixing quite a lot of annoying bugs from Vista RTM. Vista SP1 will bring most of these improvements to Vista as well, fortunately. But until then, Windows Server 2008 is my new favorite OS!
Entries (RSS)