Class B

With Class B, the first 16 bits of the address represents a network number, the rest of the address is used to number nodes.

Class B networks were assigned a quarter of the available address space. If you see an address in the range 128.0.0.0 – 191.255.255.255 then this is a class B. There are 2^16 or 65,536 possible nodes. A class B is a perfect size for a large company or a University.

16 special class B addresses are reserved for internal use only and do not route on the internet, from 172.16.0.0 to 172.31.0.0 as established by RFC1918.

In this case our subnet mask would be;

Class B addresses are identified by the subnet mask 255.255.0.0 or another way we can describe this is to call is a /16, meaning that 16 bits are used for the network number.