DNS64 & nslookup

Mark Andrews marka at isc.org
Wed Apr 11 22:58:04 UTC 2018

DNS64 server takes a AAAA lookup and if there are NOT AAAA records at the name
it then performs a A lookup for the same name and maps the results into AAAA
records and returns them.  There are additional caveats but that is the basic

It does NOT take a A lookup and return AAAA record.

A lookups get A answers.
AAAA lookups get AAAA answers.


> On 12 Apr 2018, at 8:51 am, Rick Tillery <rtillerywork at gmail.com> wrote:
> According to what I've read, that's exactly what DNS64 does. It converts A records to AAAA records. (For mixed networks, it just passes through AAAA records, but that's not in my configuration):
> "DNS64 is a mechanism for synthesizing AAAA resource records (RRs) from A RRs." - https://tools.ietf.org/html/rfc6147
> "DNS64 describes a DNS server that when asked for a domain's AAAA records, but only finds A records, synthesizes the AAAA records from the A records." - https://en.m.wikipedia.org/wiki/IPv6_transition_mechanism
> Rick
> On Apr 11, 2018 5:40 PM, "Chuck Swiger" <cswiger at mac.com> wrote:
> On Apr 11, 2018, at 3:32 PM, Rick Tillery <rtillerywork at gmail.com> wrote:
> > I'll give those tools a try, but I don't understand how my client is requesting an A record. It only has IPv6 networking. DNS64 should be requesting an A record, but that the client should see is the converted AAAA record. Is that not right?
> Nope-- DNS requests aren't going to convert an A record to a AAAA record.
> Normally, IPv6 only machines should request IPv6 AAAA records by preference, and fall back to IPv4 A records only when IPv6 isn't available.  However, your IPv6-only machine will route IPv4 traffic using 6-in-4 or NAT64 addressing, otherwise you'd get broken connectivity to IPv4-only addresses.
> Regards,
> -- 
> -Chuck
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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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