go
nss1.dfdns.msft.net are subdomains to this hostname. msft.net is a domain controlled by five nameservers at msft.net themselves. All of them are on different IP networks.

msft.net
ns-soa records
ns1.msft.net
+ 65.55.37.62 65.55.32.0/20 AS8075 -
+ --- -
ns records
ns1.msft.net
+ 65.55.37.62 65.55.32.0/20 AS8075 -
+ --- -
ns2.msft.net
+ 64.4.59.173 64.4.0.0/18 AS8075 -
ns3.msft.net
+ 213.199.161.77 213.199.160.0/20 AS8068 dns3uk.msft.net
+ --- dns3uk.msft.net
+ --- dns3.uk.msft.net
+ --- -
ns4.msft.net
+ 207.46.75.254 207.46.64.0/19 AS8069 -
ns5.msft.net
+ 65.55.226.140 65.55.192.0/18 AS8075 -
subdomains
*.dfdns.msft.net
nss1.dfdns.msft.net