RAD-ISM-900-EN-BD…
A-2
PHOENIX CONTACT
2476_en_I
The bits for the network class are followed by those for the network address and 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) (see Table A-2).
IP addresses can be represented in decimal or hexadecimal form. In decimal form, bytes
are separated by dots (dotted decimal notation) to show the logical grouping of the
individual bytes (see Figure A-2).
Figure A-2
Structure of IP Addresses
Table A-1
Class Assignments
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Class A
0
Class B
1
0
Class C
1
1
0
Class D
1
1
1
0
Class E
1
1
1
1
0
Table A-2
Network and User Class Bit Assignments
Network ID
Host ID
Class A
7 bits
Class B
14 bits
Class C
21 bits
Class D
21-bit multicast identifier
Class E
27 bits
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.
0
Network ID
Host ID
1
0
Network ID
Host ID
1
1
0
Network ID
Host ID
1
1
1
0
Identifier for multicast group
1
1
1
1
0
Reserved for future applications
Class A
0.0.0.0 - 127.255.255.255
Class B
128.0.0.0 - 191.255.255.255
7 bits
24 bits
14 bits
16 bits
21 bits
8 bits
28 bits
27 bits
Class C
192.0.0.0 - 233.255.255.255
Class D
224.0.0.0 - 239.255.255.255
Class E
240.0.0.0 - 247.255.255.255
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