RFC 1918 / START HERE
Private IPv4 addresses, before the details
Address Allocation for Private Internets is a descriptive title, not an acronym. IPv4 means Internet Protocol version 4.
RFC 1918 sets aside three IPv4 address ranges for use within privately operated networks. Different organizations can reuse them, but each cooperating network needs an unambiguous address plan.
The idea in one picture
Plan one network
Use a private range
Control the boundary
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
It conserves globally unique addresses where global uniqueness is unnecessary. The BCP explains connectivity choices, route and DNS containment, and the renumbering costs when networks join or needs change.
A familiar example
A workplace can number its printer 10.20.0.8. Another workplace may use the same number; joining those networks needs coordination. A private address does not itself provide a firewall, encryption or Internet access.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Choose the scope a host needsAn enterprise here means a network operator that controls its own address plan. Private addresses identify hosts within that enterprise, not a globally unique Internet destination.→
- Read the three reserved prefixesA slash prefix fixes the leading bits of an IPv4 address. The remaining bits vary within the block; a 12-bit prefix can split an eight-bit octet.→
- Contain routes and private packetsPrivate addresses have no global meaning. Border policy must distinguish ordinary internal routing from exporting a private route or forwarding a private-addressed packet outside.→
- Plan for reuse and renumberingTwo independent enterprises may both use the same private address. Combining their networks can turn valid local names for hosts into an ambiguous destination.→
- Bound DNS data and coordinated tunnelsPrivate address references should stay within their intended scope. DNS views and encapsulation are explicit operational designs, not properties automatically supplied by a private prefix.→
This introduction explains RFC 1918 (1996). Read the original RFC ↗