Reasons for Defining RFC 1918 Address Space

AB

RFC 1918 defines three private IPv4 address ranges that can be used within private networks, they are:

• 10.0.0.0/8
• 172.16.0.0/12
• 192.168.0.0/16

These address ranges are reserved for use within private networks and are not routable on the Internet.

The two reasons for defining RFC 1918 address space are:

A. To preserve public IPv4 address space: Public IPv4 addresses are a finite resource that are allocated and managed by regional Internet registries. Prior to the widespread adoption of NAT (Network Address Translation), every device connected to the Internet needed a unique public IPv4 address. As the number of devices on the Internet grew rapidly, the supply of available public IPv4 addresses diminished. The use of private IPv4 address space within private networks helped to alleviate the shortage of public IPv4 addresses and preserve them for use on the Internet.

B. To reduce the occurrence of overlapping IP addresses: Overlapping IP addresses occur when two devices on different networks have the same IP address. This can cause communication issues and make it difficult to manage network traffic. By using private IPv4 address space within private networks, the likelihood of overlapping IP addresses is reduced.

C. To preserve public IPv6 address space: While RFC 1918 address space is specific to IPv4, a similar concept of using private address space also exists in IPv6. Private IPv6 address ranges are defined in RFC 4193 to preserve public IPv6 address space.

D. Reduce the size of ISP routing tables: By using private IPv4 address space within private networks, the size of the global routing table used by ISPs is reduced. This is because private IP addresses are not routable on the Internet, so they do not need to be advertised to the global routing table.

E. To support the NAT protocol: Network Address Translation (NAT) is a technique that allows multiple devices on a private network to share a single public IP address. NAT is commonly used by ISPs to conserve public IPv4 address space. Private IPv4 address space is used within the private network, and the NAT device translates these private addresses to the public IP address when traffic leaves the network.