Legacy IPv4 addresses refer to the range of IPv4 addresses that were allocated in the early days of the internet, before the establishment of the current system of Regional Internet Registries (RIRs). These addresses are a significant part of the internet’s foundational infrastructure, making up around 35% of all IPv4 addresses. Initially, large quantities of IPv4 addresses were generously allocated to organizations by the Internet Assigned Numbers Authority (IANA) in the 1980s, resulting in some entities possessing millions of IPs that today are either not visible on the internet or remain unused.
The term “legacy” is used because these addresses were distributed before the RIR system was put in place. The RIR system, which began with RIPE NCC in 1992, took over the responsibility of managing IP addresses and maintaining records within their respective regions. Organizations that obtained their IP addresses before the establishment of this system, particularly before 1997, are considered holders of legacy IP addresses.
Due to the exhaustion of IPv4 addresses, which has been a pressing concern given the internet’s growth, RIRs like RIPE and ARIN have been actively seeking to reclaim unused legacy IP address space. This effort includes contacting holders of these addresses to encourage the return of unused or unadvertised IPs. In exchange, organizations are offered various benefits through agreements like the Legacy Registration Services Agreement (Legacy RSA) proposed by ARIN. This agreement provides benefits such as rights retention, reduced fees, and future fee waivers to organizations that return unused IP address space.
The legal status of legacy IPv4 address blocks has been a topic of discussion. In 2012, the General Counsel of the U.S. National Science Foundation (NSF) clarified that legacy IPv4 address holders own their number blocks, undermining claims that entities like ARIN hold authority over these addresses without a specific agreement. This clarification has implications for the emerging IPv4 address market, as it affirms the ownership rights of legacy address holders over their IP blocks.
In summary, legacy IPv4 addresses are those allocated in the early stages of the internet’s development, before the RIR system was established. These addresses represent a significant portion of the finite IPv4 space and are crucial for addressing the current shortage of available addresses. Efforts to manage these addresses include reclaiming unused space and legal clarifications regarding ownership and authority over these legacy blocks.