Originally, IPv5 was just IPv4 protocol with 64 bit addressing (instead of IPv4 s 32 bit addressing), but eventually the think-tanks from the Networking world realised that 64 bit addressing does not represent enough benefit considering the cost of transition from IPv4 to IPv5 even though increased address space was the only change. Also, limitations of IPv4 were becoming more visible, so there would eventually be a need to transition to IPv6 with 128 bit addressing and many compatibility breaking improvements to the core IPv4 protocol, which would trigger another costly transition from IPv5 to IPv6. So, the IPv5 was never really standardized, and instead the Internet Protocol migrated directly to the planned IPv6 (128 bit address along with backward compatibility breaking significant improvements from better security through mandatory support for IPsec to better routing and auto-configuration).

Version 5 of IP was assigned to an experimental protocol called ST2 (Internet Stream Protocol, version 2), which is described in RFC 1819.

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