Thus network numbers are 128.1 through 191.254. The last two octets are available for host addesses, giving 16 bits of host address. This allows for 64516 computers, which should be enough for most organizations. Finally, class C addresses use three octets, in the range 192.1.1 to 223.254.254. These allow only 254 hosts on each network, but there can be lots of these networks.
Many large organizations find it convenient to divide their network number into subnet .
For example, Rutgers has been assigned a class B address, 128.6. We find it convenient to use the third octet of the address to indicate which Ethernet a host is on. This division has no significance outside of Rutgers. A computer at another institution would send any packet whose destination address began with 128.6 on the best route to Rutgers. They would not have different routes for 128.6.4 or 128.6.5.