Python dns.resolver of a NS doesn't work on subdomains? - dnspython

Question

I'm trying to get the NS of a subdomain, but I get a NoAnswer Exception.
I suspect it's because asking for the NS is only working on the root domain, but how can I do then?
Is there a way to achieve it using dnspython or do I have to remove each subpart until the NS work?

Answer 1

Here's my answer to my own question. I finally decided to go up the ladder and remove each sub parts of the domain up to the last dot (keeping the last two parts).
Here's the code:
def ns_lookup(domain):
parts = domain.split('.')
lookup = resolver.Resolver()
lookup.timeout = 3
ns_ips = None
while len(parts) >= 2:
try:
nameservers = [a.to_text() for a in lookup.query('.'.join(parts), 'NS')]
ns_ips = [resolver.query(ns)[0].to_text() for ns in nameservers]
if len(ns_ips) > 0:
return ns_ips
except exception.Timeout:
return []
except (resolver.NoAnswer, resolver.NXDOMAIN, resolver.NoNameservers):
pass
parts.pop(0)
return False
And it works that way:
ns_ips = ns_lookup(domain)
if ns_ips is False:
return False
if len(ns_ips) == 0:
return []
lookup = resolver.Resolver(configure=False)
lookup.timeout = 3
lookup.nameservers = ns_ips
lookup.query(domain, 'A') # The entry you want.
Hope that helps anyone else.