What DNS Is Not

Jack Bates jbates at brightok.net
Mon Nov 9 17:26:16 CST 2009


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




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