IP Address Structure
| Class A: | 0nnnnnnn hhhhhhhh hhhhhhhh hhhhhhhh | netid (7bits), hostid (24 bits). |
| Class B: | 10nnnnnn nnnnnnnn hhhhhhhh hhhhhhhh | netid (14 bits), hostid (16 bits). |
| Class C: | 110nnnnn nnnnnnnn nnnnnnnn hhhhhhhh | netid (21-bits), hostid (8 bits). |
| Class D: | 1110mmmm mmmmmmmm mmmmmmmm mmmmmmmm | Multicast group 28 bits. |
Class E addresses are reserved for future use.
Subnet Masks
Subnet masks are used to separate an IP address into netid, subnetid and hostid by masking out the hostid. For example:
| IP Address: | 192.168.216.244 | (0xC0A8D8F4) |
| Net Id: | 192 | (0xC0) |
| Subnet Mask: | 255.255.255.0 | (0xFFFFFF00) |
| Host Id: | 244 | (0x000000F4) |
| Subnet Id: | 168.216 | (0x00A8D800) |
Another example:
| IP Address: | 192.168.216.244 | (0xC0A8D8F4) |
| Net Id: | 192 | (0xC0) |
| Subnet Mask: | 255.255.255.192 | (0xFFFFFFC0) |
| Host Id: | 52 | (0x00000034) |
| Subnet Id: | 168.216.192 | (0x00A8D8C0) |
Special Addresses
Address elements that resolve to all 1 bits are broadcast addresses.Net Id 0 is reserved for BOOTP.
References
- W.R. Stevens.
TCP/IP Illustrated, Volume 1: The Protocols.
Prentice Hall
ISBN 0- 20163346-9
.
