【My Study Note】NAT, Non-Routable Address Space and the Limits of IPv4
NAT, Non-Routable Address Space and the Limits of IPv4
The IANA has been in charge of distributing IP addresses since 1988. Since that time, the internet has expanded at an incredible rate. The 4.2 billion possible IPv4 addresses have been predicted to run out for a long time and they almost have.
For some time now, the IANA has primarily been responsible for assigning address blocks to the five RIRs (Regional Internet Registries).
The five RIRs
- AFRINIC: Serves the continent of Africa
- ARIN: Serves the United States, Canada and parts of the Caribbean
- APNIC: Responsible for most of Asia, Australia and New Zealand, and Pacific Island nations
- LACNIC: Covers Central and South America and any parts of the Caribbean not covered by ARIN
- RIPE: Serves Europe, Russia, the Middle East, and portions of Central Asia
These five RIRs have been responsible for assigning IP address blocks to organizations within their geographic areas and most have already run out.
The IANA assigned the last unallocated slash eight network blocks to various RIRs on February 3rd, 2011. Then in April 2011, APNIC ran out of addresses. RIPE was next, in September of 2012. LACNIC ran out of addresses to assign in June 2014. And ARIN did the same in September 2015. Only AFNIC has some IPs left, but those are predicted to be depleted by 2018.
This is, of course, a significant crisis for the internet.
IPv6 will eventually resolve these problems. But implementing IPv6 worldwide is going to take some time. For now, we wanted to continue to grow and we want more people and devices to connect to it but without IP addresses to assign, a workaround is needed.
Example of Workaround
NAT and non-routable address space are some examples of workaround. Non-routable address space was defined in RFC1918 and consists of several different IP ranges that anyone can use. And unlimited networks can use non-routable address space internally because internet routers won’t forward traffic to it.
This means there’s never any global collision of IP addresses when people use those address spaces. Non-routable address space is largely usable today because of technologies like NAT.
With NAT, you can have hundreds even thousands of machines using non-routable address space. Yet, with just a single public IP, all those computers can still send traffic to and receive traffic from the internet.
All you need is one single IPv4 address and via NAT, a router with that IP can represent lots and lots of computers behind it. It’s not a perfect solution, but until IPv6 becomes more globally available, non-routable address space and NAT will have to do.