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copied!<p>Here's my attempt at this. It uses the system's standard DNS server for looking up the root server for the top-level domain and for resolving the names of the various DNS servers along the chain, which I think is appropriate because those names would presumably change very infrequently.</p> <pre><code>import dns import dns.name import dns.query import dns.resolver def get_authoritative_nameserver(domain, log=lambda msg: None): n = dns.name.from_text(domain) depth = 2 default = dns.resolver.get_default_resolver() nameserver = default.nameservers[0] last = False while not last: s = n.split(depth) last = s[0].to_unicode() == u'@' sub = s[1] log('Looking up %s on %s' % (sub, nameserver)) query = dns.message.make_query(sub, dns.rdatatype.NS) response = dns.query.udp(query, nameserver) rcode = response.rcode() if rcode != dns.rcode.NOERROR: if rcode == dns.rcode.NXDOMAIN: raise Exception('%s does not exist.' % sub) else: raise Exception('Error %s' % dns.rcode.to_text(rcode)) rrset = None if len(response.authority) > 0: rrset = response.authority[0] else: rrset = response.answer[0] rr = rrset[0] if rr.rdtype == dns.rdatatype.SOA: log('Same server is authoritative for %s' % sub) else: authority = rr.target log('%s is authoritative for %s' % (authority, sub)) nameserver = default.query(authority).rrset[0].to_text() depth += 1 return nameserver import sys def log(msg): print msg print get_authoritative_nameserver(sys.argv[1], log) </code></pre> <p>Here's some sample output:</p> <pre><code>Looking up com. on 192.168.255.10 l.gtld-servers.net. is authoritative for com. Looking up stackoverflow.com. on 192.41.162.30 ns1.p19.dynect.net. is authoritative for stackoverflow.com. Looking up meta.stackoverflow.com. on 208.78.70.19 Same server is authoritative for meta.stackoverflow.com. 208.78.70.19 </code></pre>

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