Comment by InfamousRece
1 month ago
At my previous place IPv6 was useable (I was getting /60 prefix rather than /64 I’m getting now) but the prefix was changing often - several times per day. This was annoying because every prefix change all addresses of my devices changed too. So in practice I always used private IPv4 addresses to connect to them. A NAT would solve this issue.
Well, delegated IPv6 prefixes are supposed[1] to be static or somewhat persistent, but some ISPs do this, yes. This is most likely a practice carried over from IPv4 where there is a small pool of addresses. Fortunately in my experience it's not too common: most ISPs that deployed IPv6 did it the right way.
Anyway, to get persistent addresses you can set up a ULA prefix (the equivalent of RFC 1918 addresses) and a simple prefix translation[3]. This is a form of NAT, but unlike the usual IPv4 NAT (actually NAPT) it doesn't deal with ports, so it's slightly less annoying problematic. There also are a few more techniques, like using mDNS and writing firewall rules that match the suffix of the client addresses, but not many CPE allows for this.
[1]: https://www.ripe.net/publications/docs/ripe-690/#53-why-pers...
[2]: https://en.wikipedia.org/wiki/Unique_local_address
[3]: https://openwrt.org/docs/guide-user/network/ipv6/ipv6.nat6
You don't need prefix translation to use a ULA prefix. You just configure both the ULA and the ISP-delegated GUA prefixes simultaneously.
Right, the ULA prefix theoretically has lower preference, so it should only be selected to reach hosts in the LAN and the GUA for everything else, but I don't know how well softwares handle this in practice.
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