Alex Balashov wrote:
When I write applications that make DNS queries, I expect the request to turn NXDOMAIN if the host does not exist - HTTP as well as non-HTTP, but especially non-HTTP.
Actually, the one I hate is when they return NXDOMAIN for any RR type other than A, breaking DNS. Most common is AAAA to return NXDOMAIN, which immediately has the effect of breaking the ability to fallback to A (why query for another RR, when the domain doesn't exist?). Several high end load balancers have the ability to do this according to the content providers I have addressed the matter with.
As a side note, any IPv6 capable stack which has determined there is IPv6 connectivity (through 6to4, native, teredo, etc) cannot access these sites. For an example (an ongoing issue) see www.txu.com. Responds to A, gives NXDOMAIN to AAAA.
I will not shame the high profile websites that have fixed their loadbalancers/DNS servers, but everyone on this list knows and has probably used them.
Jack
