go
audns.optus.net has one IP number , which also has a corresponding reverse pointer. id.au, asn.au, net.au, com.au, gov.au and at least three other hosts use this as a nameserver. optus.net is a domain controlled by two nameservers at optus.net themselves. They are on different IP networks. Incoming mail for optus.net is handled by one mailserver at optusnet.com.au. optus.net has one IP number. audns.optus.net is hosted on a server in Australia.

audns.optus.net
a records
 
+ 211.29.133.32 211.29.128.0/19 AS4804 -
+ --- -

optus.net
a records
 
+ 211.29.132.105 211.29.128.0/19 AS4804  
+ ---  
ns-soa records
 
+   AS?  
+ ---  
ns records
ns1.optus.net
+ 211.29.133.110 211.29.128.0/19 AS4804 -
+ --- -
ns2.optus.net
+ 211.31.132.21 211.31.128.0/19 AS4804 -
mx records
extmail.optusnet.com.au
+ 211.29.133.14 211.29.128.0/19 AS4804 -
+ --- -
ip numbers of host
211.29.133.32
ptrs of ip numbers
audns.optus.net
ip numbers using ptr to this host
211.29.133.32
domains using this as nameserver
1.6.e164.arpa
asn.au
com.au
fiattasmania.com.au
gov.au
id.au
net.au
org.au
used as nameserver but missing in zone
1.6.e164.arpa
fiattasmania.com.au