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. ['18.104.22.168'] [TTL=172800] ns3.serverfault.com. ['22.214.171.124'] [TTL=172800] ns4.serverfault.com. ['126.96.36.199'] [TTL=172800] ns2.serverfault.com. ['188.8.131.52'] [TTL=172800]
However, the zone file itself, which is authoritative, tells me that actually the nameservers are here instead:
ns2.serverfault.com ['184.108.40.206'] [TTL=300] ns1.serverfault.com ['220.127.116.11'] [TTL=300] ns3.serverfault.com ['18.104.22.168'] [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?