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Is there a reason why adoption has been so abysmally slow? Like surely all the big players have updated their networking equipment by now, and surely every piece of enterprise-grade kit sold in the last 20 years has supported v6. The only arguments I've ever heard against ipv6 that made any sense are that: 1: it's hard to remember addresses, which is mayyyyybe valid for homelab enthusiast types, but for medium scale…
IPv6 is a recursive WTF. It might _look_ like a conservative expansion of IPv4, but it's really not. A lot of operational experience and practices from IPv4 don't apply to IPv6. For example, in IPv4 each host has one local net address, and the gateway uses NAT to let it speak with the Internet. Simple and clean. In IPv6 each host has multiple global addresses. But if your global connection goes down, these addresses…
It's not significantly worse on v6 compared to v4. Yes, in theory, you can send v4 packets without DF and helpful routers will fragment for you. In practice, nobody wants that: end points don't like reassembling and may drop fragments; routers have limited cpu budget off the fast path and segment too big is off the fast path, so too big may be dropped rather than be fragmented and with DF, an ICMP may not always be sent, and some routers are configured in ways where they can't ever send an ICMP.
PMTUd blackholes suck just as much on v4 and v6. 6rd tunnels maybe make it a bit easier to hit if you advertise mtu 1500 and are really mtu 1480 because of a tunnel, but there's plenty of derpy networks out there for v4 as well.