What DNS Is Not
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.
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