The term ‘B-net’ is commonly (but often erroneously) used to describe an Internet Protocol (IP) Network with the netmask 255.255.0.0, meaning it contains 65 536 IP-addresses. Since the introduction of Classless Inter-Domain Routing (CIDR) in 1993, that netmask now corresponds to a ‘/16’. In the predecessor to CIDR, Classful Networking, the class with netmask ‘255.255.0.0’ was ‘1 B’, which is why the terms became erroneously synonymous.
The tool above will check all the networks within the entire /16. Simply enter the first two segments of the IP-address (eg: a.b, or 172.16) and the tool will do the rest!