| There were five IP address classes
in use before the majority of industry switched to classless routing.
There were A, B, C, D, and E. Class A addresses were used for networks
with a very large number of total hosts. Class B was designed for use on
medium to large networks, and C for small local area networks (LANs).
Class D and E were set aside for multicast and experimental purposes. In
the following table, the four octets that make up an IP address (a, b,
c, and d respectfully) are displayed in how they were distributed in
classes A, B, and C. classes A, B, and C. |
|---|
| Class | 1st Octet Decimal Range | 1st Octet High Order Bits | Network/Host ID (N=Network, H=Host) | Default Subnet Mask | Number of Networks | Hosts per Network (Usable Addresses) |
|---|---|---|---|---|---|---|
| A | 1 – 126* | 0 | N.H.H.H | 255.0.0.0 | 126 (27 – 2) | 16,777,214 (224 – 2) |
| B | 128 – 191 | 10 | N.N.H.H | 255.255.0.0 | 16,382 (214 – 2) | 65,534 (216 – 2) |
| C | 192 – 223 | 110 | N.N.N.H | 255.255.255.0 | 2,097,150 (221 – 2) | 254 (28 – 2) |
| D | 224 – 239 | 1110 | Reserved for Multicasting | |||
| E | 240 – 254 | 1111 | Experimental; used for research | |||
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