DNS64 & nslookup

[Mark Andrews]

Because nslookup and dig are specialised DNS testing tools.  They
don’t use getaddrinfo to perform test lookups.  getaddrinfo is the
function that most applications use as part of the connection process.

> On 12 Apr 2018, at 8:33 am, 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?
> 
> Rick
> 
> On Wed, Apr 11, 2018, 5:27 PM Chuck Swiger <cswiger at mac.com> wrote:
> On Apr 11, 2018, at 3:09 PM, Rick Tillery <rtillerywork at gmail.com> wrote:
> > I appear to have my NAT64+DN64 IPv6 -> IPv4 network configured correctly, as I can access IPv4 only Internet sites, e.g. from my browser.  But some tools don't seem to work the way I think they should.
> > 
> > One example is nslookup.  If do nslookup ipv4.google.com, I get:
> > 
> > $ nslookup ipv4.google.com
> > Server:         2001:4:1f:98::2
> > Address:        2001:4:1f:98::2#53
> > 
> > Non-authoritative answer:
> > ipv4.google.com canonical name = ipv4.l.google.com.
> > Name:   ipv4.l.google.com
> > Address: 216.58.218.110
> > 
> > Shouldn't the address (last line) be an IPv6 address (prefixed IPv4 address, created by NAT64, such as 64:ff9b::216.58.218.110)?
> 
> Nope.  Whether your local system connects to IPv4 addresses via NAT64-formatted IPv6 addresses is unrelated to DNS lookups of A or AAAA records.  If you ask for an A record, you will get IPv4 address(es) back or 0 records, not an IPv6 address.
> 
> By the way, debugging DNS issues by using nslookup is difficult; try switching to dig and consider the results of running "dig -t a ipv4.l.google.com." and "dig -t aaaa ipv4.l.google.com."
> 
> 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