Just the other day we had a problem regarding IPv4 and IPv6 at the office. We were migrating our SVN server from one machine to another and we had to set up the other machine properly so everybody could access the SVN server. Unfortunately, something wasn't working out. We were able to install an "svn serve" application, register the server as a Windows service that runs on boot up, but it wasn't working. Every time we tried to connect, the host machine would actively refuse a connection. We were puzzled. We've tried many different things and in the end all we had to do is specify an explicit listen-host as 0.0.0.0 to force the server to use IPv4 because Windows 7 tries to use IPv6 wherever it can and the SVN protocol doesn't work on IPv6 yet. What an irony.