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Recycling IP Addresses

When we talk about recycling we usually mean physical goods and the materials they contain. In the modern connected world these aren’t the only valuable resources though, and there are others that might lack physical existence but are still finite and need to be conserved. One of the most important is IP addresses.

Most modern computers, tablets and smartphones use the TCP/IP protocol to communicate and share data with each other, and this set of standards is built around the concept of IP addresses. A traditional IPv4 address consists of four numbers, separated by periods; each number can be anywhere between 0 and 255. In fact the whole IP address is a single 32-bit number that can be broken down into subnets or operated as a single large network. Each device on the network needs to have a unique IP address; for it to work properly duplicates cannot exist. The problem is that using a 32-bit number means there are a total of about 4.3 billion addresses available – and the pool of available ones is running out.

When the IPv4 standard was written in 1981 it was hard to believe there would ever be so many connected devices, but the unbelievable has become reality and in fact the 4.3 billion limit has already been exceeded. To keep the internet working some hard work has been necessary. The main effort has been towards developing and deploying IPv6, which uses 128-bit addresses and so offers 3.4×1038 unique identifiers – enough for every person on earth to have millions of devices. However many systems still depend on the older technology, so it’s vital to get the most possible use out of the existing pool.

One common technique is Network Address Translation, or NAT. This allows multiple devices to connect to the internet through a single external IP address. There are limitations to NAT, because it doesn’t always allow end to end connectivity between individual devices, but it can significantly increase the number of consumer devices that can be operated. Most broadband routers function as NAT systems – there is one IP address that connects to the internet, but a large number of devices can be connected downstream using private IP addresses (usually 192.168.xxx.xxx).

Larger-scale efforts are also being made to free up addresses. Many large blocks were previously allocated to organizations that aren’t using all of them, and the body that allocates address space, IANA, has the option of reclaiming and reissuing all or part of these blocks. There are technical issues with this, because some hardware isn’t set up to use certain address ranges, but it could potentially add up to a billion more addresses.

The IPv4 address space can’t last in the long term – whatever measures are taken the growing number of connected devices, especially the always-on ones envisaged for the “internet of things”, will exhaust the supply. The future lies with IPv6. In the meantime, however, clever use of NAT and reclaimed address blocks should keep things going until the newer protocol becomes more widespread.