It’s probably not a big deal and NAT etc. is no protection but it gave me the heebie jeebies.
Bad generalization. I'm sure policy about this differs a lot, but my consumer ISP definitely reassigns my home's v4 address periodically. I don't track it closely, but it seems that when my ONT power cycles more often than not it pulls a new v4 address.
Now, basing my privacy/security on this would be bad, but to GP's point, if I was using a static v6 block, not only would this address never change, each device in my LAN would have an extra identifier attached to it. External hosts wouldn't merely be able to identify "my house", but traffic from "my phone", "my kid's switch", and "my spouse's phone" would all have distinct addresses.
Of course, my ISP doesn't do v6 at all, so there's no dilemma :')
But it does seem like it would be far more likely de facto for an ISP to not randomly rotate v6 networks, except maybe to discourage hosting on consumer connections?
This is not true.
IPv6 stack allocates at least 3 addresses:
- Link-local - "Permanent" Address derived from the subnet and MAC - Temporary address that changes several times per day
The default address for new connections is always the temporary address. So IP-based tracking from outside your network will be no better than it was before from one day to the next—the /64 will be the only constant here, just as your router's WAN IPv4 is for v4 connections.
My understanding is v6 has two different autoconf schemes, DHCPv6 and a more "native" solution. Do these both always result in interfaces having multiple (routable) addresses?
Most of my IPv6 experience has been setting it up on aforementioned VPS, and being rewarded with slow OS updates, since NetBSD's default CDN, Fastly, blackholes PMTUD, so I had to drop the MTU on the interface just to get v6 TCP connections to work at all[0]. And for point-to-point networking in an overlay VPN, where I just discovered that Chromium has an 11-year outstanding "bug" where it refuses to perform AAAA lookups if you don't have public IPv6 routing.
[0] I could switch mirrors, but the bandwidth drop isn't quite bad enough for me to bother...
> My understanding is v6 has two different autoconf schemes, DHCPv6 and a more "native" solution. Do these both always result in interfaces having multiple (routable) addresses?
The answer to that is "yes," but only insofar as DHCP is _not_ the norm for IPv6 networks. If you're planning to use DHCP to assign network addresses in an IPv6 range, you would run it in addition to using automatic configuration, and DHCPv6 would be responsible only for the "permanent" IPv6 address. Automatically-configured addresses (via RA with SLAAC or whatever) would still create the temporary address that you'd use for outbound internet connectivity, and the DHCP address hangs around for your use in DNS and for hosting "permanent" services like a webserver or whatever.
You've hit on one of the subtler problems of IPv6 being that it requires more things being let through the edge firewall[0], but given a stateful IPv6 firewall on the client side, the onus is on the hosting service's admin to ensure that works correctly (AFAIK).
Also, v6 supports "privacy extensions", essentially randomizing the host portion of the address and periodically rotating it, so it is not accurate to say your address would never change.