4.1 Subnetting
Subnetting is nothing but creating networks within a network. Subnetting allows an organization with a single IP address (Class A /Class B /Class C) to have multiple subnetworks, thus allowing several physical networks with in the organization.
Addresses are written using decimal numbers separated by decimal points. This is called dotted decimal notation of expressing IP addresses.
| Class | Format | Leading Bit Pattern | Network address Range | Maximum networks | Maximum host/nodes |
| A | N.H.H.H | 0 | 0 - 126 | 127 | 16,777,214 |
| B | N.N.H.H | 10 | 128 - 191 | 16,384 | 65,534 |
| C | N.N.N.H | 110 | 192 - 223 | 20,971,52 | 254 |
| D | Not defined | 1110 | 224 -255 | Not defined | Not defined |
| E | Not defined | 1111 | 240-255 | Not defined | Not defined |
Network address of all zeros means "This network or segment.
Network address of all 1s means "all networks", same as hexadecimal of all Fs.
Network number 127 is reserved for loopback tests.
Host(Node) address of all zeros mean "This Host (Node)".
Host (Node) address of all 1s mean "all Hosts (Nodes) " on the specified network.
1. The address range and the corresponding binary values for the first octet of IP classes are as given below:
Class A
0. 0. 0. 0 = 00000000.00000000.00000000.00000000
127.255.255.255 = 01111111.11111111.11111111.11111111
0nnnnnnn.HHHHHHHH.HHHHHHHH.HHHHHHHH
Class B
128. 0. 0. 0 = 10000000.00000000.00000000.00000000
191.255.255.255 = 10111111.11111111.11111111.11111111
10nnnnnn.nnnnnnnn.HHHHHHHH.HHHHHHHH
Class C
192. 0. 0. 0 = 11000000.00000000.00000000.00000000
223.255.255.255 = 11011111.11111111.11111111.11111111
110nnnnn.nnnnnnnn.nnnnnnnn.HHHHHHHH
Class D
224. 0. 0. 0 = 11100000.00000000.00000000.00000000
239.255.255.255 = 11101111.11111111.11111111.11111111
1110XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX
Class E
240. 0. 0. 0 = 11110000.00000000.00000000.00000000
255.255.255.255 = 11111111.11111111.11111111.11111111
1111XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX
2. The range of numbers from 224.0.0.0 to 239.255.255.255 are used for multicast packets. This is known as Class D address range.
