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What secrets does the 240/4 range hide?
The issue of the unused IPv4 address range with the 240/4 prefix has occasionally become a topic of discussion in the developer and network engineering community. This range of 268 million addresses was reserved by IANA for "future address modes" as stated in RFC 1112. However, despite the gradual depletion of free IPv4 addresses, this reserve remains untapped, which is puzzling to experts: why are a quarter of a billion IPv4 addresses still not used when the global network is in dire need of additional resources?
In 2008, two draft proposals were submitted for the use of band 240/4. One of them, the Wilson-class-e project, was to use this range in private networks, which could help large organizations migrate to IPv6 in a dual-stack (IPv4/IPv6) architecture. This solution would allow large networks to avoid conflicts with existing private bands (1918bis), such as 10/8, which are already in active use, and would make it easier for network equipment to communicate with traffic translation over NAT.
Another project, Fuller-240space, proposed to make the range available for general use, since by 2010-2012 it was predicted that free IPv4 addresses would be completely exhausted. However, as experts noted, deploying support for addresses from the 240/4 range on millions of devices around the world would require a tremendous effort, which would divert attention from the main task - an accelerated transition to IPv6.
As a result, discussions about the fate of the 240/4 band, which flared up in 2008-2009, have practically come to naught. The problem of IPv4 address pool depletion became critical, and the network community switched to developing IPv6 transition mechanisms such as Dual-Stack Lite (RFC 6333) and NAT464 (RFC 6877), which took precedence over using the 240/4 range.
Nevertheless, despite the oblivion of official proposals, the topic periodically returns. In recent years, various studies have been conducted to determine whether it is still possible to use this range in practice. In 2022, RIPE Labs conducted tests that showed that Amazon AWS uses addresses from the 240/4 range for internal needs, indicating its partial private use.
RIPE Atlas tests using servers with addresses in the 240/4 range showed that out of 7,600 samples, only 34 were able to reach the server, all of which were on the Verizon Business network. Later, in 2024, a second measurement revealed even worse results — out of 190 nodes, only 1 was able to connect to a server in the Czech Republic, which was located on the Quantcom (AS29208) network. Extensive testing with 1000 nodes confirmed that the reachability of servers with addresses from this range is extremely low (967 responding probes reported failure to reach the server), which is due to the lack of routing support for this prefix on most network devices and routers.
The problem is that many routers, end devices, and network equipment still do not support traffic with addresses in the 240/4 range. This is because, at the software level, many devices have a rule of ignoring packets with such addresses, since they were reserved for "future use" and were not intended to work on real networks.
Network equipment, NAT systems, and other intermediate nodes such as Carrier-Grade NAT (CGN) also often block traffic with addresses from this range, which significantly limits their use at the global level. Even if individual networks, such as Quantcom in the Czech Republic, can carry traffic with such addresses, global routing remains a challenge.
Studies have shown that attempts to deploy support for the 240/4 band on a global scale will be extremely difficult and unjustified. According to the latest tests, the availability of these addresses at the global level is only 0.0452%. This means that the vast majority of hosts on the Internet will not be able to communicate with servers that use addresses from this range. The main reasons for this are routing, host-level filtering, and intermediate network hardware level blocking.
Therefore, the use of the 240/4 range as a global unified address space is unlikely. However, its private use, as tests have shown, is already taking place in limited conditions, for example, for the internal needs of large chains such as Amazon. This indicates that, despite the formal absence of reallocation of this IANA range, network operators can already use it in private networks without the risk of conflict with other unified addresses.
To sum up, it is worth noting that the global network is not ready for the mass introduction of the 240/4 band as a public unified address space. Private use of this range remains the most sensible approach, and networks wishing to use these addresses can do so under controlled conditions.
Source
The issue of the unused IPv4 address range with the 240/4 prefix has occasionally become a topic of discussion in the developer and network engineering community. This range of 268 million addresses was reserved by IANA for "future address modes" as stated in RFC 1112. However, despite the gradual depletion of free IPv4 addresses, this reserve remains untapped, which is puzzling to experts: why are a quarter of a billion IPv4 addresses still not used when the global network is in dire need of additional resources?
In 2008, two draft proposals were submitted for the use of band 240/4. One of them, the Wilson-class-e project, was to use this range in private networks, which could help large organizations migrate to IPv6 in a dual-stack (IPv4/IPv6) architecture. This solution would allow large networks to avoid conflicts with existing private bands (1918bis), such as 10/8, which are already in active use, and would make it easier for network equipment to communicate with traffic translation over NAT.
Another project, Fuller-240space, proposed to make the range available for general use, since by 2010-2012 it was predicted that free IPv4 addresses would be completely exhausted. However, as experts noted, deploying support for addresses from the 240/4 range on millions of devices around the world would require a tremendous effort, which would divert attention from the main task - an accelerated transition to IPv6.
As a result, discussions about the fate of the 240/4 band, which flared up in 2008-2009, have practically come to naught. The problem of IPv4 address pool depletion became critical, and the network community switched to developing IPv6 transition mechanisms such as Dual-Stack Lite (RFC 6333) and NAT464 (RFC 6877), which took precedence over using the 240/4 range.
Nevertheless, despite the oblivion of official proposals, the topic periodically returns. In recent years, various studies have been conducted to determine whether it is still possible to use this range in practice. In 2022, RIPE Labs conducted tests that showed that Amazon AWS uses addresses from the 240/4 range for internal needs, indicating its partial private use.
RIPE Atlas tests using servers with addresses in the 240/4 range showed that out of 7,600 samples, only 34 were able to reach the server, all of which were on the Verizon Business network. Later, in 2024, a second measurement revealed even worse results — out of 190 nodes, only 1 was able to connect to a server in the Czech Republic, which was located on the Quantcom (AS29208) network. Extensive testing with 1000 nodes confirmed that the reachability of servers with addresses from this range is extremely low (967 responding probes reported failure to reach the server), which is due to the lack of routing support for this prefix on most network devices and routers.
The problem is that many routers, end devices, and network equipment still do not support traffic with addresses in the 240/4 range. This is because, at the software level, many devices have a rule of ignoring packets with such addresses, since they were reserved for "future use" and were not intended to work on real networks.
Network equipment, NAT systems, and other intermediate nodes such as Carrier-Grade NAT (CGN) also often block traffic with addresses from this range, which significantly limits their use at the global level. Even if individual networks, such as Quantcom in the Czech Republic, can carry traffic with such addresses, global routing remains a challenge.
Studies have shown that attempts to deploy support for the 240/4 band on a global scale will be extremely difficult and unjustified. According to the latest tests, the availability of these addresses at the global level is only 0.0452%. This means that the vast majority of hosts on the Internet will not be able to communicate with servers that use addresses from this range. The main reasons for this are routing, host-level filtering, and intermediate network hardware level blocking.
Therefore, the use of the 240/4 range as a global unified address space is unlikely. However, its private use, as tests have shown, is already taking place in limited conditions, for example, for the internal needs of large chains such as Amazon. This indicates that, despite the formal absence of reallocation of this IANA range, network operators can already use it in private networks without the risk of conflict with other unified addresses.
To sum up, it is worth noting that the global network is not ready for the mass introduction of the 240/4 band as a public unified address space. Private use of this range remains the most sensible approach, and networks wishing to use these addresses can do so under controlled conditions.
Source
