My problem with IPv6 is that my ISP (Xfinity) won't give me a static prefix, so every now and again it changes.

Unlike IPv4, my LAN addresses include the prefix, so every time they change it, all my LAN addresses change.

Combined with the lack of DHCP6 support in many devices, this means reverse DNS lookups from IP to hostname can't be done, making identifying devices by their IP essentially impossible.

I think you’re conflating multiple things there. There’s nothing magical about IPv4 that gives your LAN addresses stability when your ISP changes your IP prefix. That’s provided by your router doing network address translation. You send a packet from your address which is 192.168.0.42 (a local address), and your router changes the bytes in the packet so that it comes from X.Y.Z.W (your router’s public address). If you really wanted it to your router could do the same thing for IPv6.

IPv6 also has local addresses, but a lot more of them. Anything starting with fd00::/8 is a local address with 40 bits available as the network number. So you can set up your local network with the prefix fdXX:XXXX:XXXX::/48 (where the Xs are chosen randomly) as the prefix and still have 16 bits left over for different subnets if you want. These addresses do not change when your ISP changes your public prefix.

And if you want to add reverse dns for SLAAC addresses then just have your router listen for ICMPv6 Neighbor Announcement addresses and use them to update your DNS server as appropriate. Or configure your servers to use stable addresses based on their MAC address rather than random addresses (which are better for privacy), and then just configure the DNS as you add and remove servers.

> Unlike IPv4, my LAN addresses include the prefix, so every time they change it, all my LAN addresses change.

Yes, a topic of active discussion at the IETF. See perhaps BCP RFC 9096, "Improving the Reaction of Customer Edge Routers to IPv6 Renumbering Events":

* https://datatracker.ietf.org/doc/html/rfc9096

And informational RFC 8978, "Reaction of IPv6 Stateless Address Autoconfiguration (SLAAC) to Flash-Renumbering Events":

* https://datatracker.ietf.org/doc/html/rfc8978

A few drafts, like "Improving the Robustness of Stateless Address Autoconfiguration (SLAAC) to Flash Renumbering Events":

* https://datatracker.ietf.org/doc/html/draft-ietf-6man-slaac-...

Using ULA seems to be what a lot of folks recommend:

* https://en.wikipedia.org/wiki/Unique_local_address

you should advertise a local prefix (anything in fd00::/8) in your network and it should just work. no need to use the isp-provided prefix for lan.

My ISP will route as many /64s to me as I want (I think I get a /48 by default, I guess if I want more than 64k subnets I’d have to justify it)

So I don’t have the changing ip issue. I do however have an issue if I want to change ISP as it’s a whole mess of rules to update rather than a couple of dns entries and two dst nat rule (one per public IP)

I believe the idea in v6 if you have multiple prefixes on the same network - including a local fc00::/7 one for local services. Layers and layers of things to break.

Use a ULA (unique local address) for everything internal that you want shorter. It's just like rfc1918 addresses except you don't need NAT.

Well.. that's because with ipv6 you're not technically on a lan everything is exposed by default unless you set it all up differently.

Is reverse dns even a thing outside of irc and forgetting to give command line tools the "don’t be slow" flag?