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

[Jim Reid]

> On 27 Apr 2017, at 09:13, Peng Yonghua <pyh at vodafonemail.de> wrote:
> 
> I wrote a simple module to query the domain via DNS system, more exactly, query the domain from its parent nameservers.
> for example, given yahoo.com, I check the domain name from com's nameservers.
> if rcode is NXDOMAIN then domain not taken. if rcode is NOERROR then domain has taken.
> 
> How do you think of it? 

Not a lot.

Domain names can be known to the parent registry (and therefore “taken”) but not published in the DNS. For example TLD registries can and do suspend or lock domain names because the registrant has done something naughty or hasn’t get paid a renewal fee or whatever.

Now you might (or might not) be able to get a domain name's status information from the registry’s whois service if that exists. Just because a name doesn’t resolve in the DNS it doesn’t mean someone will be able to register that name. For instance the domain name foobar.rfc1035.com does not exist, I’m not willing to register it and there’s no whois service for subdomains of rfc1035.com either.