> Is there an alternative, though? Certainly some people didn't like the changes of ND vs ARP and such, but once you're changing the address length, you have t

> Is there an alternative, though? Certainly some people didn't like the changes of ND vs ARP and such, but once you're changing the address length, you have to alter the data structure on every bit of networking code, and any transition is going to be a slog. IPv4 data structures have four bytes/octets (4B) for addresses. So how do you fit 8B of addresses in 4B structures? You don't. So you have to update every network element—host (desktop, laptop, mobile, embedded), router, switch, firewall—to have a new data structure (and maybe new function/system calls, as the old ones assume the old structures). So all devices have to have updated network stacks, including long-lived ones that sometimes are not touched for a decade+. And not just pure networking code: anything that touches (e.g.) DNS as well, as A records are 4B-only as well, so you need a new record type and deploy new DNS server and resolver code everywhere. But of course if you have a 4B-only network elements/devices, they cannot talk to 8B-only devices/services, so you have to create translation mechanisms because some devices may not yet have the update 8B-capable network stack. And sometimes an 8B network is an island in a sea of 4B, so you have to have tunneling. Of course some may have both 4B and 8B, and want to talk to something has also has 4B and 8B, so now you have to have code for source/destination selection. And of course as long as IPv4 works there's little inherent motivation to go to any kind of IPng. See "TCP and UDP with Bigger Addresses (TUBA), A Simple Proposal for Internet Addressing and Routing" for part of the discussion from back in the day (1993): * https://datatracker.ietf.org/doc/html/rfc1347 https://datatracker.ietf.org/doc/html/rfc1347