DNS64 & nslookup

Mark Andrews marka at isc.org
Wed Apr 11 23:48:33 UTC 2018

Firstly, you can tell nslookup to make AAAA queries “nslookup -query=aaaa”.

nslookup is a really old tool which is why it make A queries by default.
It predates even the concept of IPv6 (which dates from ~1995).  The same
also applies to dig which is slightly younger than nslookup.

Secondly, I would look at other mechanisms than DNS64/NAT64 to provide
IPv4 as-a-service.  It really has a lot of issues which the other
mechanisms don’t.

Thirdly, I wouldn’t rush to running IPv6-only.  It does have its advantages
but they come with serious drawbacks.  At this stage IPv6-only is still
niche only.

DS-Lite, MAP-T, MAP-E, 464XLAT are all alternatives to running DNS64/NAT64.


> On 12 Apr 2018, at 9:26 am, Mark Boolootian <booloo at ucsc.edu> wrote:
>>> As far as I know, a host with on an IPv6 address is only ever
>>> going to perform AAAA lookups.  I'd be very interested to know
>>> if there are cases where that isn't true.
>> Well, if you run nslookup or dig -t a, you're asking for A records
>> explicitly.
> Ah, true that.  Does nslookup do that by default?
>> OK, fair enough.  If you ask a DNS64 server for an A record, it should still
>> give you back an A record.  If you ask for an AAAA RR, then you will get back an
>> AAAA record, even if it has to synthesize an A record into a 6-in-4 IPv6 address.
> Yes.  And this was what seemed weird about the original
> question.  In my experience, an IPv6 only host (and IPv6
> only means no routable v4 address - so you might have
> 169.254, but nothing else) only emits AAAA lookups.  But
> maybe I need to look more carefully.  I'm working towards
> building an IPv6 only environment here, and my (often
> erroneous) thinking presupposes certain behavior.
> cheers,
> mark
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org

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