RFC 790 (rfc790) - Page 2 of 15
Assigned numbers
Alternative Format: Original Text Document
RFC 790 September 1981
Assigned Numbers
Network Numbers
ASSIGNED NETWORK NUMBERS
This list of network numbers is used in the internet address [33].
The Internet Protocol (IP) uses a 32 bit address and divides that
address into a network part and a "rest" or local address part. The
division takes 3 forms or classes.
The first type, or class a, of address has a 7-bit network number
and a 24-bit local address. This allows 128 class a networks.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| NETWORK | Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class A Address
The second type, or class b, of address has a 14-bit network
number and a 16-bit local address. This allows 16,384 class b
networks.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0| NETWORK | Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class B Address
The third type, or class c, of address has a 21-bit network number
and a 8-bit local address. This allows 2,097,152 class c
networks.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 0| NETWORK | Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class C Address
One notation for internet host addresses commonly used divides the
32-bit address into four 8-bit fields and specifies the value of each
field as a decimal number with the fields separated by periods. For
example, the internet address of ISIF is 010.020.000.052.
This notation will be used in the listing of assigned network
Postel