I'm trying to setup an IP address range. It's asking for:
A) IP Address Range (but it will only accept a normal IP address)
B) Mask or Prefix
I need to allow 192.168.100.100 - 192.168.100.120
How can I make that happen?
You need to specify the IP Address and a proper subnet mask. I just used IP Subnet Calculator to calculate the subnet mask for the address 192.168.100.100. So if you specify the subnet 255.255.255.240 for 14 nodes.
By entering a lot of individual addresses.
100-120 is not doable in a single masked entry. It just does not align properly with any mask possible.
Be also carefull whether what you do makes any sense. Users with enough rights can change their ip address - so, this is only barefuly usable in limited scenarios within a LAN. I would suggest not filtering by IP address, but using user identities / accounts if possible.