In the IPv4 IP address space, there are five classes: A, B, C, D and E. Each class has a specific range of IP addresses (and ultimately dictates the number of devices you can have on your network). Primarily, class A, B, and C are used by the majority of devices on the Internet. Class D and class E are for special uses.
The list below shows the five available IP classes, along with the number of networks each can support and the maximum number of hosts (devices) that can be on each of those networks. The four octets that make up an IP address are conventionally represented by a.b.c.d - such as 127.10.20.30.
Additionally, information is also provided on private addresses and loop address (used for network troubleshooting).
Class A Public Address
Class A addresses are for networks with large number of total hosts. Class A allows for 126 networks by using the first octet for the network ID. The first bit in this octet, is always set and fixed to zero. And next seven bits in the octet is all set to one, which then complete network ID. The 24 bits in the remaining octets represent the hosts ID, allowing 126 networks and approximately 17 million hosts per network. Class A network number values begin at 1 and end at 127.
- IP Range: 126.96.36.199 to 188.8.131.52
- First octet value range from 1 to 127
- Subnet Mask: 255.0.0.0 (8 bits)
- Number of Networks: 126
- Number of Hosts per Network: 16,777,214
Class B Public Address
Class B addresses are for medium to large sized networks. Class B allows for 16,384 networks by using the first two octets for the network ID. The two bits in the first octet are always set and fixed to 1 0. The remaining 6 bits, together with the next octet, complete network ID. The 16 bits in the third and fourth octet represent host ID, allowing for approximately 65,000 hosts per network. Class B network number values begin at 128 and end at 191.
- Range: 184.108.40.206 to 220.127.116.11
- First octet value range from 128 to 191
- Subnet Mask: 255.255.0.0 (16 bits)
- Number of Networks: 16,382
- Number of Hosts per Network: 65,534
Class C Public Address
Class C addresses are used in small local area networks (LANs). Class C allows for approximately 2 million networks by using the first three octets for the network ID. In class C address three bits are always set and fixed to 1 1 0. And in the first three octets 21 bits complete the total network ID. The 8 bits of the last octet represent the host ID allowing for 254 hosts per one network. Class C network number values begin at 192 and end at 223.
- Range: 192.0.0.0 to 18.104.22.168
- First octet value range from 192 to 223
- Subnet Mask: 255.255.255.0 (24 bits)
- Number of Networks: 2,097,150
- Number of Hosts per Network: 254
Class D Address Class
Classes D are not allocated to hosts and are used for multicasting.
- Range: 22.214.171.124 to 126.96.36.199
- First octet value range from 224 to 239
- Number of Networks: N/A
- Number of Hosts per Network: Multicasting
Class E Address Class
Classes E are not allocated to hosts and are not available for general use. They are reserved for reseach purposes.
- Range: 240.0.0.0 to 255.255.255.255
- First octet value range from 240 to 255
- Number of Networks: N/A
- Number of Hosts per Network: Research/Reserved/Experimental
Within each network class, there are designated IP address that is reserved specifically for private/internal use only. This IP address cannot be used on Internet-facing devices as that are non-routable. For example, web servers and FTP servers must use non-private IP addresses. However, within your own home or business network, private IP addresses are assigned to your devices (such as workstations, printers, and file servers).
- Class A Private Range: 10.0.0.0 to 10.255.255.255
- Class B Private APIPA Range: 169.254.0.0 to 169.254.255.255
- Automatic Private IP Addressing (APIPA) is a feature on Microsoft Windows-based computers to automatically assign itself an IP address within this range if a Dynamic Host Configuration Protocol (DHCP) server is not available. A DHCP server is a device on a network that is responsible for assigning IP address to devices on the network.
- Class B Private Range: 172.16.0.0 to 188.8.131.52
- Class C Private Range: 192.168.0.0 to 192.168.255.255
- IP Range: 127.0.0.1 to 127.255.255.255 are network testing addresses (also referred to as loop-back addresses)