> That's actually "once all routers and end devices are updated to support them". As the classic spamsolutions.txt says, "requires immediate total cooperation f

> That's actually "once all routers and end devices are updated to support them". As the classic spamsolutions.txt says, "requires immediate total cooperation from everybody at once". This point cannot be emphasized enough. To quote Hyrum's Law [0]: > With a sufficient number of users of an API, it does not matter what you promise in the contract: all observable behaviors of your system will be depended on by somebody. And for networking this means that, even if the NRO decreed that all reserved/testing IPv4 blocks [1] would be publicly routable and turned over to the RIRs for allocation, those blocks would be effectively unusable. It doesn't matter how many RFCs you produce saying "you must assume these addresses will be someday used", networking hardware and software has ossified around specific expectations pertaining to what addresses are valid and invalid, what protocols are acceptable, etc. A great example of this is TLS 1.3: due to protocol ossification, the spec had to be rewritten to be more similar to TLS 1.2 because network middleboxes kept assuming it was a threat and blocking the connections [2]. This is also the reason SCTP has yet to gain widespread adoption, and why any new layer 4 protocol is likely doomed to fail: networking hardware hates anything that deviates from the acceptable traffic patterns which have been hard-coded in, RFCs be damned. Imagine if previously unused IPv4 blocks started getting allocated. You'd be cut off from most of the internet, and most of the internet would be cut off from you. It wouldn't be enough, of course - even if all 2^32 addresses were publicly routable, that's still not even enough for 1 IP per person, you'd still have to rely on NAT, and all the problems it causes. (This is also why I think suggestions like "organizations like Apple who have a /8 but barely use it should just give up those extra IPv4s" are misguided and really understate of the scale of the problem - it's just putting a band-aid on an open fracture that cut your femoral artery.) [0]: https://www.hyrumslaw.com/ https://www.hyrumslaw.com/ [1]: https://en.wikipedia.org/wiki/Reserved_IP_addresses#IPv4 https://en.wikipedia.org/wiki/Reserved_IP_addresses#IPv4 [2]: https://blog.cloudflare.com/why-tls-1-3-isnt-in-browsers-yet/ https://blog.cloudflare.com/why-tls-1-3-isnt-in-browsers-yet...