If you go on intodns.com and type in stackoverflow.com, the parent server tells me that nameservers for the domain are here:
ns1.serverfault.com. ['198.252.206.80'] [TTL=172800]
ns3.serverfault.com. ['69.59.196.217'] [TTL=172800]
ns4.serverfault.com. ['69.59.196.122'] [TTL=172800]
ns2.serverfault.com. ['198.252.206.81'] [TTL=172800]
However, the zone file itself, which is authoritative, tells me that actually the nameservers are here instead:
ns2.serverfault.com ['198.252.206.81'] [TTL=300]
ns1.serverfault.com ['198.252.206.80'] [TTL=300]
ns3.serverfault.com ['69.59.196.217'] [TTL=300]
Can any one explain why ns4.serverfault.com. would be listed as a nameserver when it isn't? What would happen if the resolver went to this address trying to find the A record for stackoverflow.com?
aa
flag set. If it were not authoritative, it would either be responding based on data cached based on other queries (which requires theaa
flag be cleared), with a redirection toward the root servers (usually.
) or with a query refusal. You can use dig as exemplified in my answer to your other question to see this for yourself. Try asking ns4.serverfault.com for www.example.net and observe the difference (just don't overdo it).