Understanding RFC 1918 Private IP Address Ranges
The Internet Engineering Task Force (IETF) has reserved a specific range of IP addresses for use in private networks. These ranges are defined in RFC 1918 and are not routed on the internet. This allows for the creation of large networks without the need for globally unique IP addresses, conserving the limited supply of public IP addresses.
RFC 1918 Private IP Address Ranges
The following are the three ranges of IP addresses reserved for private use:
- 10.0.0.0 to 10.255.255.255 (10/8 prefix)
- 172.16.0.0 to 172.31.255.255 (172.16/12 prefix)
- 192.168.0.0 to 192.168.255.255 (192.168/16 prefix)
Key Concepts
Private IP addresses are used for communication within a private network and are not globally unique. They are not routed on the internet and cannot be used to directly access resources on the internet.
Public IP addresses are globally unique and are used for communication on the internet. They are required for devices on a private network to access resources on the internet.
NAT (Network Address Translation) is a technique used to allow devices with private IP addresses to communicate with the internet using a single public IP address. NAT translates the private IP address of a device to the public IP address of the NAT gateway when the device initiates communication with the internet.
Subnetting
Subnetting is the process of dividing a larger network into smaller networks, called subnets. This can be done to improve network performance, increase security, or to more efficiently use the available IP address space.
When subnetting a private network, it is important to consider the size of the subnets and the number of hosts that will be on each subnet. The size of the subnet is determined by the subnet mask, which is a 32-bit number that masks a portion of the IP address to indicate the network portion of the address.
Example
Consider a private network with the IP address range 192.168.0.0 to 192.168.255.255. This range can be divided into 256 subnets, each with a size of 256 hosts, by using a subnet mask of 255.255.255.0.
192.168.0.0 255.255.255.0
The first three octets (192.168.0) of the IP address represent the network portion of the address, and the last octet (0) represents the host portion. The subnet mask of 255.255.255.0 indicates that the first three octets are the network portion and the last octet is the host portion.
- RFC 1918 reserves the following ranges of IP addresses for private use: 10.0.0.0 to 10.255.255.255 (10/8 prefix), 172.16.0.0 to 172.31.255.255 (172.16/12 prefix), and 192.168.0.0 to 192.168.255.255 (192.168/16 prefix).
- Private IP addresses are used for communication within a private network and are not globally unique.
- Public IP addresses are globally unique and are used for communication on the internet.
- NAT (Network Address Translation) is a technique used to allow devices with private IP addresses to communicate with the internet using a single public IP address.
- Subnetting is the process of dividing a larger network into smaller networks, called subnets.