UnrealIRCd supports the CIDR notation when allowing/disallowing IP's. This can be used in bans, allow blocks, oper::mask, etc. etc. If you prefer to use CIDR, you can use it.
An example of CIDR would be 127.0.0.0/8 which matches 127.0.0.0 through 127.255.255.255. In this example we could just as easily have written 127.*.
For more information see Wikipedia - CIDR.