IPv4
- 32 bits
- Written as four decimal numbers called octets
- Octet --> 8 bits
- Each octet can be any number from 0 to 255
- Divided into two parts
Private IPs
- A company can use private IPs on its private networks
- IEEE recommends the following:
10.0.0.0 through 10.255.255.255.255172.16.0.0 through 172.31.255.255192.168.0.0 through 192.168.255.255
Classes
- Dividing line between network and host portions is determined by numerical range IP address falls in
- Class A, B, and C are available for use on the internet
- Classes D and E are not available for general use:
- Class D begins with octets 224-239 --> use for multicasting
- Class E begins with octets 240-254 --> used for research
| Class |
Network octets |
Octet Range |
Default Mask |
Approx. number of possible networks |
Approx. number of IP aπddresses in each network |
| A |
1.x.y.z to 126.x.y.z |
1-126 |
255.0.0.0 |
126 |
16 million |
| B |
128.0.x.y to 191.255.x.y |
128-191 |
255.255.0.0 |
16,000 |
65,000 |
| C |
192.0.0.x to 223.255.255.x |
192-223 |
255.255.255.0 |
2 million |
254 |
Reserved IPs
| IP Address(es) |
Function |
255.255.255.255 |
Used to broadcast messages by TCP/IP background processes. Message is read by every node on the network. |
0.0.0.0 |
Unassigned |
127.0.0.1 through 127.255.255.254 |
Uses for research or your own computer (loopback address) |
169.254.0.1 through 169.254.255.254 |
Used to create APIPA address when a computer configured for DHCP first connects to the network and is unable to lease an IPv4 address from DHCP server. |
Subnet Calculations
- Subnetting
- Alters the rules of classful IPv4 addressing
- Called classless addressing
- Borrow bits that would represent host information in classful addressing and use those bits to represent network information
- Increase number of bits available for the network ID
- Reduce number of bits available for identifying hosts
- Reduce the number of usable host addresses in each network
Computer Science Networking IP Address