Can the Forgotten IPv4 Class E Space Help Solve the IP Exhaustion Crisis?

Origin Story of IPv4 Class E

IPv4 address space was originally divided into classes A‑E, with the Class E range (240.0.0.0 – 255.255.255.255) reserved for experimental use and never allocated to the public Internet.

As IPv4 addresses have become scarce, the market now charges separately for IPv4 blocks, with a /24 often costing around $10,000.

Real‑World Expectations

The ultimate answer to IPv4 exhaustion is IPv6 deployment, but many networks still rely on IPv4, making the fate of Class E an interesting question.

Class E as a Local Unicast Space

Because private networks and infrastructure consume large address pools, Class E could be repurposed as a massive private addressing space, offering up to 524,288 /24 blocks.

AWS network devices sometimes use 240.0.0.0/4.

Some home and small‑business networks have experimented with Class E.

Canonical’s “fan” network utilizes Class E.

Cloudflare can map IPv6 addresses into Class E for legacy IPv6‑unsupported systems.

Vendor Support Situation

Operating‑system support for Class E includes Linux kernels released after 2008, Android (2009 onward), macOS/iOS (post‑2009), and OpenBSD (from October 2022). Windows and NetBSD/FreeBSD do not support it.

Router support varies:

JunOS requires routing-options martians 240/4 orlonger allow to accept Class E.

Arista EOS needs use ipv4 routable 240.0.0.0/4.

Many other vendors outright reject Class E addresses.

Unexpected OSPF Behaviour

OSPF may forward routes containing Class E through routers that cannot actually handle the addresses, causing traffic loss or default routing.

Surprising Real‑World Tests

A lab experiment showed that when a path contains a router that does not support Class E, traffic to Class E destinations is dropped, even though OSPF advertises the route.

Quantcom’s tests with RIPE Atlas probes showed roughly 50 % of end‑devices could reach Class E addresses, while BGP reachability across the Internet was only about 0.04 %.

Several autonomous systems (e.g., AT&T Europe‑ME‑AF, VEON/Beeline, Cloudflare’s Prague PoP, Akamai, Quad9) accepted the Class E prefix, but most networks filtered it.

Should You Use Class E Space?

In general, the answer is no—unless you control the entire network and cannot migrate to IPv6, Class E can be useful for large private addressing. Global adoption faces major hurdles: software incompatibility, lack of policy support from IANA/IETF, and the need to allocate the space among regional registries.

Given the difficulty of updating billions of devices, IPv6 remains the sensible path forward.