Kevin Reeuwijk reports that “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.