AFAIK class B networks range between 128.0.0.0 and 191.255.255.255. The net mask is per default 255.255.0.0.
These networks can be subnetted.
PIX Firewall Series Configuration Guide, Version 4.0
•For a Class B address, which ranges from 128.0.0.0 to 191.255.255.255, the network address is in the first two octets and the host ID is in the last two. This permits 65,536 hosts to be represented by a single Class B IP address.
•For a Class C address, which ranges from 192.0.0.0 to 223.255.255.255, the network address is in the first three octets and the host ID is in the last octet. This permits 256 hosts to be represented by a single Class C IP address
