Structure Of An Ipv4 Address - Siemens SCALANCE W770 Series Configuration Manuals

Description
2.6 Interface identifiers and addresses
2.6.4

Structure of an IPv4 address

Address classes
IP address range
1.x.x.x through 126.x.x.x
128.0.x.x through 191.255.x.x
192.0.0.x through 223.255.255.x
224.0.0.0 - 239.255.255.255
240.0.0.0 - 255.255.255.255
An IP address consists of 4 bytes. Each byte is represented in decimal, with a dot separating
it from the previous one. This results in the following structure, where XXX stands for a number
between 0 and 255:
XXX.XXX.XXX.XXX
The IP address is made up of two parts, the network ID and the host ID. This allows different
subnets to be created. Depending on the bytes of the IP address used as the network ID and
those used for the host ID, the IP address can be assigned to a specific address class.
Subnet mask
The bits of the host ID can be used to create subnets. The leading bits represent the address
of the subnet and the remaining bits the address of the host in the subnet.
A subnet is defined by the subnet mask. The structure of the subnet mask corresponds to that
of an IP address. If a "1" is used at a bit position in the subnet mask, the bit belongs to the
corresponding position in the IP address of the subnet address, otherwise to the address of
the computer.
Example of a class B network:
The standard subnet address for class B networks is 255.255.0.0; in other words, the last two
bytes are available for defining a subnet. If 16 subnets must be defined, the third byte of the
subnet address must be set to 11110000 (binary notation). In this case, this results in the
subnet mask 255.255.240.0.
To find out whether two IP addresses belong to the same subnet, the two IP addresses and
the subnet mask are ANDed bit by bit. If both logic operations have the save result, both IP
addresses belong to the same subnet, for example, 141.120.246.210 and 141.120.252.108.
Outside the local area network, the distinction between network ID and host ID is of no
significance, in this case packets are delivered based on the entire IP address.
Note
In the bit representation of the subnet mask, the "ones" must be set left-justified; in other words,
there must be no "zeros" between the "ones".
34
Max. number of networks
126
16383
2097151
Multicast applications
Reserved for future applications
SCALANCE W770/W730 acc. to IEEE 802.11n Command Line Interface
Max. number of hosts/net‐
work
16777214
65534
254
Configuration Manual, 09/2017, C79000-G8976-C324-08
Class CIDR
A /8
B /16
C /24
D
E