The IPv6 Transition

I'm not kidding. For example, Android doesn't support stateful DHCPv6. And DHCPv6 doesn't have the _basic_ feature of DHCPv4: hostnames. You can't easily use it to do a quick survey of your network.

Then you have that @#&(^(&!@^ that is ULA.

With IPv4 we have a very useful pattern: you create an "internal" network that is stable and predictable. It's routed to the outside world through NAT. If the external connection goes down, the internal network is unaffected.

With IPv6 you're supposed to have ULA and the global routed addresses in parallel. So now the external connection goes down, and the router withdraws the prefix from the router advertisement. Half of the hosts lose their external addresses, but keep the ULAs. Half of the hosts don't implement prefix withdrawal, and keep both their ULAs and the normal addresses. Congrats, now these hosts can't talk to each other due to the ULA addresses being less preferred.

And of course, IPv6 hasn't improved on the PMTU. So if you're running an Internet service, you need to use something like 1400 MTU to make sure some of the misconfigured tunneled clients don't get shafted. There's now an RFC that makes it useful: https://datatracker.ietf.org/doc/html/rfc9268 , but it's Experimental and it'll need ~20 years to be deployed anyways.

IPv6, a story of recursive utter failure at all levels...

Just skip DHCPV6, just use SLAAC. Plus I've never seen DHCP hostnames work.

Now I just ping ff02::1 multicast to see what devices are on my network. Unfortunately much software makes it a pain to use link-local addresses but they're really convenient as they normally don't change across networks.

> Half of the hosts don't implement prefix withdrawal, and keep both their ULAs and the normal addresses. Congrats, now these hosts can't talk to each other due to the ULA addresses being less preferred.

I've had similar issues with crappy devices not relinquishing DHCPv4 IPs properly. Always fun trying to figure out why your laptop is dropped off your network after 20 minutes because it honors DHCP.

The lack of proper prefix widthdrawl sucks. Though it's something software should be able to handle by preferring ULA addresses when communicating locally.

Here's how a part of my IPv4 network looks in my router's control panel: https://imgur.com/a/xZDUfqw , I can easily set up permanent local IPv4 addresses for the fixed infrastructure, and I can easily see which hosts are alive.

Yes, it's not 100% perfect, but it works most of the time just fine. Even with crappy IoT devices.

Here's how it looks for IPv6 and SLAAC: https://imgur.com/a/DiUNqTC - good luck trying to make sense of it.