PostgreSQL pg_hba.conf problem adding a host?
You need to specify an IP address of the form: 192.168.0.1/24 where "/24" is an alternative representation of your Subnet-Mask.
For a local area network you often see 255.255.255.0 as a Subnet-Mask. Each part of that Mask can be translated to an 8-Bit representation (255 = 11111111). So for 3 x 255 you've got 3x 8-Bit which leads to a total of 24-Bits and there you go. Of course, you'll find more detailed explanations on the internet.
Just use http://www.subnet-calculator.com/ or ask your provider for your Subnet-Mask.