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Windows Server 2008 R2 DNS issues

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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