This week we stumbled upon some weirdness in our new 2008 R2 DNS servers. A couple of URLs, for example www.smhi.se and www.stockholm.se could not be resolved from a 2008 R2 server. The existing 2003 servers with the same configuration worked perfectly. After thorough troubleshooting we found out that there is a new default setting in Windows Server 2008 R2 regarding the EDNS-protocol that caused the issues. Not all of the DNS servers around the internet are able to handle EDNS , but in 2008 R2 this protocol is enabled by default. Normally you would think there is a fallback mechanism to standard DNS protocol if an EDNS request fails, but Windows Server does not have that. The solution was simply to disable EDNS by using the command: dnscmd /config /EnableEDNSProbes 0 Scott Forsyth has written more about this issue and how he found the solution: http://weblogs.asp.net/owscott/archive/2009/09/15/windows-server-2008-r2-dns-issues.aspx
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