User manual

Startup and Functions
6874_en_09 PHOENIX CONTACT 3-3
3.1.2.2 Assigning IP Addresses
The IP address is a 32-bit address, which consists of a network part and a user part. The
network part consists of the network class and the network address.
There are currently five defined network classes; Classes A, B, and C are used in modern
applications, while Classes D and E are hardly ever used. It is therefore usually sufficient
if a network device only "recognizes" Classes A, B, and C.
Figure 3-1 Position of bits within the IP address
With binary representation of the IP address the network class is represented by the first
bits. The key factor is the number of "ones" before the first "zero". The assignment of
classes is shown in the following table. The empty cells in the table are not relevant to the
network class and are already used for the network address.
The bits for the network class are followed by those for the network address and the user
address. Depending on the network class, a different number of bits are available, both for
the network address (network ID) and the user address (host ID).
IP addresses can be represented in decimal or hexadecimal form. In decimal notation,
bytes are separated by dots (dotted decimal notation) to show the logical grouping of the
individual bytes.
B i t 1 B i t 3 2
6 1 4 6 A 0 5 6
Bit 1 Bit 2 Bit 3 Bit 4 Bit 5
Class A 0
Class B 10
Class C 110
Class D 1110
Class E 11110
Network ID Host ID
Class A 7 bits 24 bits
Class B 14 bits 16 bits
Class C 21 bits 8 bits
Class D 28-bit multicast identifier
Class E 27 bits (reserved)
The decimal points do not divide the address into a network and user address. Only the
value of the first bits (before the first "zero") specifies the network class and the number
of remaining bits in the address.