Tweaks to IPv4 could free up 'hundreds of millions of addresses'

And 'tweaks' is doing some heavy lifting, there

It may be nearly three years since the world officially exhausted all of the available IPv4 internet addresses, but now a new initiative has been proposed that could free up hundreds of millions of addresses that are currently unused – or are they?

While the world is still slowly moving towards broader adoption of the newer IPv6 protocol, which offers a vast address space, the widespread continued use of IPv4 has caused problems because all available ranges of the roughly 4.3 billion addresses it supports have largely been allocated.

Now it seems that Seth Schoen, formerly a senior staff technologist at the Electronic Frontier Foundation and co-founder of Let's Encrypt, has made proposals collectively labelled either the IPv4 Unicast Extensions Project or the IPv4 Cleanup Project (both are used on the project's GitHub page).

Writing in a post on the APNIC blog, Schoen detailed his proposals.

These are also outlined in four Internet Drafts filed with the Internet Engineering Task Force (IETF), which call for four categories of "special" addresses that are currently unavailable for standard addressing purposes to be redefined as ordinary unicast addresses, meaning they should no longer be regarded as reserved, invalid, or loopback addresses.

The reasons for the existence of these special addresses go back to the creation of the IPv4 version of the Internet Protocol in the early 1980s, but many of them have never been used for the purpose that they were reserved for, according to Schoen, yet have continued to be treated as special addresses.

Those four categories of addresses that the project is aiming at comprise the lowest address in each IPv4 subnet, 240/4, 0/8 and 127/8. Each was reserved for a different reason, and Schoen acknowledges that each one presents a different set of challenges to change.

Of the four, the lowest address fix is regarded as the least problematic. It proposes eliminating a duplicate broadcast address within each local network segment.

The standard broadcast address on a subnet is the highest one (i.e. 255 on a 24-bit subnet which uses 8 bits for the host addresses), but for historical reasons the "zeroth" address (i.e. 0) is also reserved, according to Schoen.

Changing this only frees up a single address per subnet, but allows organizations to "take a small step to unilaterally increase the efficiency of their use of their existing IPv4 allocations."

The other changes require code-level changes in IPv4 stack implementations, which will no doubt set alarm bells ringing among any IT admin staff out there along with network software engineers.

However, Schoen claims that some of these changes are in widespread use already, particularly the proposed changes for the 240/4 addresses that were reserved as a future-use Class E network block, comprising a total of 256 million addresses.

Changing these into recognized unicast addresses was previously proposed to the IETF more than a decade ago and apparently implemented in several operating systems now running in millions of nodes on the internet, and "has not caused any problems over the past decade," he states.

The 0/8 address range comprises another 16 million addresses that were reserved for potential device auto configuration based around ICMP messages, but these are effectively unused (apart from

Likewise, 127/8 represents another 16 million address block that was reserved as loopback addresses, and this is maintained despite the fact that virtually all applications use only a single loopback address (

These addresses will gradually become more useful as more implementations accept them as valid address space

Schoen's proposal is to reduce the range of this block so that only 127.0/16 is reserved for local loopback purposes.

Whether these changes are really necessary is debatable, since many organizations that are still using IPv4 will be sitting behind a network address translation (NAT) gateway that presents a small number of IP addresses to the outside world and operates a private addressing scheme on the internal network.

Nevertheless, Schoen believes that these measures will prove useful during the drawn-out IPv4 to IPv6 transition, if there continues to be demand for IPv4 space.

"We are continuing to encourage implementers to make the required changes, and developing software patches to support them. These addresses will gradually become more useful as more implementations accept them as valid address space," he wrote.

The proposals have already met some understandable resistance.

"Testing and changing all devices that know that 240/8, 0/8, and 127/8, etc, are 'special' is a bigger job than making them just use IPv6," tweeted Adrian Kennard, who runs UK ISP Andrews & Arnold. "The 0 address being usable probably only helps local networks." ®

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