Technical data

Class Decimal Max.
value in number of
octet 1 devices in
the network
A Network Computer Computer Computer 0 to 127 16 777 215
B Network Network Computer Computer 128 to 191 65 535
C Network Network Network Computer 192 to 223 255
114 Theoretical and general applications www.westermo.com
Addressing in a network
Before we describe how an IP address is built up we need to explain a few concepts:
… An IP address consists of four bytes.
… One byte is 8 data bits, for example, 11000000, which corresponds to the deci-
mal value 192, see byte 1 in the example opposite.
… In turn, addresses are allocated in different classes (A, B, C, D and E) where the
class describes an address interval. There are currently five address classes, of
these the first three are used (A-C) for different network types, where the IP
address is divided into a network and computer part. There are also the groups
D and E. A D address is a multicast-address while an E address has been saved
for future use.
… IP addresses in class A, B and C networks are divided into two parts, a
network part and a computer part.
A, B or C networks differ in the number of bits utilised for network and device
identity:
The A class network identity comprises 8 bits (1 byte), B class 16 bits and the
C-class 24 bits. This makes it possible to address a different number of devices
in respective networks, also see sub-network division below.
Class First byte Address interval
A 0xxx xxxx 0.0.0.0 to 127.255.255.255
B 10xx xxxx 128.0.0.0 to 191.255.255.255
C 110x xxxx 192.0.0.0 to 223.255.255.255
D 1110 xxxx 224.0.0.0 to 239.255.255.255
E 1111 xxxx 240.0.0.0 to 247.255.255.255
Byte 1234
192
. 168
. 3 . 23
B A C K