Yes, the DNS server originates from another subnet than the configured local network.
What do you mean with /32?
Since your DNS server is in a different subnet, you will have to enter their IP's in the DNS section and push a route to that network, which is what viragomann described. The /32 is CIDR notation and has to do with routing. In this case, if your DNS server was on 192.168.100.10/24, instead of pushing a route to the entire network (i.e. 192.168.100.0/24), you could just push a route to the host by entering 192.168.100.10/32, which would isolate access to the DNS server only instead of the entire network it sits on.
Is the ip only not sufficient?
For the DNS servers, yes, but not for the "IPv4 Local Network/s" section or any other network portion of the config.