Specifications

1 - 4
The address management was once carried out in this class unit. Nowadays the
class address with the variable-length border bit number is used for ensuring the
effective use of the address space.
(2) Management by class address
The management was once carried out in class unit. Nowadays, due to the
shortage of IP address, the class address with the variable-length network part is
used for ensuring the effective use of the address space.
1111 1111 000000
IP address
(Sub)net mask
Prefix length
Network part
Host part
All 1
All 0
The IP address of which host part which has all 0 for the bits is a network address
(in the Ethernet unit). "/" may be added to the end of the IP address for clearly
specifying the network address length (prefix length), and also the bit length of the
network address part may be added.
The netmask is commonly used for a historical reason. The netmask has all 1 for
the network part and all 0 for the host part.
As it is divided to manage the network (sub-networking), the netmask is also
called "subnet mask".
Example: For the IP address 192.168. 10. 68 and the prefix length 26 bits
11000000.10101000.00001010.01000100 / 26
192 . 168 . 10 . 68 / 26
C0 . A8 . A . 44 / 26
Binary number
Decimal number
Hexadecimal number
Network part (26)
Host part (6)
Number
after "/" is
prefix length.
Information examples when setting the IP address to the host
Information Address Address value (Binary) Remark
IP address 192.168. 10. 68/26 1100 0000 1010 1000 0000 1010 0100 0100
(Sub)net mask 255.255.255.192 1111 1111 1111 1111 1111 1111 1100 0000
Network address 192.168. 10. 64/26 1100 0000 1010 1000 0000 1010 0100 0000
Broadcast address 192.168. 10.127 1100 0000 1010 1000 0000 1010 0111 1111 Address of which host part is 1.