I don't have a LAN's DNS server or a DHCPv6. BTW, I have had an IPv6-only home network for 10 years, with NAT64 and 464XLAT.
You still haven't solved my puzzle or even understood what's happening. The current source address selection rules result in hosts prefering a GUA address pair over ULA. This _will_ result in broken connectivity when GUA addresses change.
There is currently no standards-compliant way to solve my challenge, except getting an ASN, an IPv6 assignment, and announcing it through your uplinks. Which I've also done in my home network, btw.
There's an in-progress RFC to change this, by preferring ULA-ULA address pairs over GUA-GUA. So it might be usable some time in the 2030-s ( https://www.ietf.org/archive/id/draft-ietf-6man-rfc6724-upda... ).
And no, this is not a theoretic problem. It affects protocols like SIP or even mDNS that exchange the IP addresses. They will consistently prefer unstable GUAs over ULAs.
[–] simoncion 4 hours ago
[–] cyberax 3 hours ago
mDNS exists. As does SIP and SMB.
I first discovered the ULA/GUA issue when my TimeMachine backup dropped mid-session when I was testing Internet connection failover. Apple later fixed it by allowing multiple SMB sessions in parallel and preferring IPv4 connections. I have a pure IPv6-only network, as I said.
The same issue happens with SIP, as phones send their own addresses during the media connection negotiation.
(I have another funny story about SIP: Asterisk used to send a Cartesian product of available codecs and IP addresses, so if you had IPv6 privacy addresses on, it eventually accumulated enough of them to overflow the MTU, causing connections to silently drop)
[–] simoncion 3 hours ago
Check out my research on this issue. [0] The results might surprise you.
Yeah, that's why you think that this is a "puzzle".
Though, it does invalidate every complaint you've made about IP source address priority. The only ways you'll get multiple addresses for a given host are to either hard-code them, or use DNS [0]. Given that you're not using DNS, then you either have automation to update all those hard-coded configs, or you do it all by hand. Either way, you're deliberately recording addresses that you don't control for your LAN hosts, and considering it a "puzzle" when you have trouble reaching those LAN hosts when your upstream provider changes their address.
[0] Given that every resolver I've ever used pulls data from '/etc/hosts', I'm considering that to be part of DNS for the purposes of this conversation. I'm also considering Avahi and friends to be DNS. [1]
[1] And if you've talked to any long-term Avahi user, you've certainly heard about its habit of -on daemon or host restart- erroneously considering host name of the machine it's running on to be "in use" and appending a "-N" to the end of it. The remarkable eagerness of Avahi to engage this collision-avoidance mechanism makes it entirely unsuitable for discovery of LAN hosts whose hostname is actually important. This fact breaks my heart, but Avahi has been doing this shit for a very, very long time, so it's probably never going to get fixed.