[bit_logic]

This whole discussion reminds me of the beautiful design of UTF-8. They used the lower bits to be ASCII which made backwards compatibility so much easier. It also reminds me of the failure of Intels Itanium and the success of AMD x64. Engineers often want to abandon backwards compatibility to make a new "beautiful" design, but it's the design that has full backwards compatibility that's actual impressive.

[x0x0]

It reminds me of python 3. Basically, a huge chunk of people (in my case, scientific programming) get an enormous mess and nothing at all of value until... 3.6 maybe (the infix matrix mult operator). Stunningly, people weren't enthused about this deal.

[krupan]

So well said! Those are great comparisons.

[liquidpele]

It would maybe be okay at the router to break some things, but ffs even in software I have to choose? Why do I need both ping and ping6 this is stupid!! They really screwed up by making it a breaking change to the OS and not just internet routing.

[Dagger2]

They didn't screw up. They made it a breaking change to OSs because it had to be a breaking change to OSs. If anyone screwed up here, it was the people who made v4, not the ones that made v6.

For ping, I think it originally had different binaries because ICMPv4 and ICMPv6 are different protocols, but Linux has had a dual-stack `ping` binary for a very long time now. You can just use `ping` for either address family.

[elcritch]

The whole ping vs ping6 seems more likely than lazy developers.