go
f.nic.ch has one IP number , but the reverse is ch1.dnsnode.net. ch1.dnsnode.net point to the same IP. ch use this as a nameserver. Incoming mail for nic.ch is handled by two mailservers at switch.ch. Two mailservers have the same IP number. nic.ch has one IP number. f.nic.ch is hosted on a server in Sweden even though the hostname implies Switzerland.

f.nic.ch
a records
 
+ 194.146.106.10 194.146.106.0/24 AS8674 ch1.dnsnode.net
+ --- ch1.dnsnode.net

nic.ch
a records
 
+ 130.59.31.247 130.59.0.0/16 AS559  
+ ---  
mx records
aletsch.switch.ch
+   AS?  
+ ---  
medel.switch.ch
+   AS?  
ip numbers of host
194.146.106.10
ptrs of ip numbers
ch1.dnsnode.net
hostnames sharing ip with a-records
ch1.dnsnode.net
domains using this as nameserver
ch