[dns-operations] check if a domain has been registered via DNS

[Viktor Dukhovni]

> On Apr 27, 2017, at 2:16 PM, Viktor Dukhovni <ietf-dane at dukhovni.org> wrote:
> 
> Some subdomains of public suffix parent domains are CNAMEs, and only
> the target of the CNAME has NS records.

Below is a better example:

nic.co.                 876     IN      CNAME   cointernet.com.co.
cointernet.com.co.      600     IN      NS      pdns196.ultradns.biz.
cointernet.com.co.      600     IN      NS      pdns196.ultradns.info.
cointernet.com.co.      600     IN      NS      pdns196.ultradns.com.
cointernet.com.co.      600     IN      NS      pdns196.ultradns.net.
cointernet.com.co.      600     IN      NS      pdns196.ultradns.co.uk.
cointernet.com.co.      600     IN      NS      pdns196.ultradns.org.

That is an *actual* CNAME in the ccTLD zone.  Other examples include:

domain.co.              CNAME   cointernet.co.
ava.com.de.             CNAME   forwarding.centralnic.com.
balseal.com.de.         CNAME   forwarding.centralnic.com.
bwin.com.de.            CNAME   forwarding.centralnic.com.
cross.com.de.           CNAME   forwarding.centralnic.com.
java.com.de.            CNAME   forwarding.centralnic.com.
kaiser.com.de.          CNAME   forwarding.centralnic.com.
main.com.de.            CNAME   forwarding.centralnic.com.
next.com.de.            CNAME   forwarding.centralnic.com.
sony.com.de.            CNAME   forwarding.centralnic.com.
tnt.com.de.             CNAME   forwarding.centralnic.com.
jobs.lk.                CNAME   topjobs.lk.
topjob.lk.              CNAME   topjobs.lk.

-- 
	Viktor.