6 ms·

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

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.

rnhmjoj 8mo ago
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-persistent-prefix-assignments-are-recommended https://www.ripe.net/publications/docs/ripe-690/#53-why-pers... [2]: https://en.wikipedia.org/wiki/Unique_local_address https://en.wikipedia.org/wiki/Unique_local_address [3]: https://openwrt.org/docs/guide-user/network/ipv6/ipv6.nat6 https://openwrt.org/docs/guide-user/network/ipv6/ipv6.nat6
- Dagger2 8mo ago
  You don't need prefix translation to use a ULA prefix. You just configure both the ULA and the ISP-delegated GUA prefixes simultaneously.
  - rnhmjoj 8mo ago
    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.
    - Dagger2 8mo ago
      Source address selection is usually left to the kernel, so that part should be okay. It'll pick a GUA source for a GUA destination unless you've changed the labels with `ip addrlabel`.

rnhmjoj 8mo ago

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-persistent-prefix-assignments-are-recommended https://www.ripe.net/publications/docs/ripe-690/#53-why-pers... [2]: https://en.wikipedia.org/wiki/Unique_local_address https://en.wikipedia.org/wiki/Unique_local_address [3]: https://openwrt.org/docs/guide-user/network/ipv6/ipv6.nat6 https://openwrt.org/docs/guide-user/network/ipv6/ipv6.nat6

Dagger2 8mo ago
You don't need prefix translation to use a ULA prefix. You just configure both the ULA and the ISP-delegated GUA prefixes simultaneously.
- rnhmjoj 8mo ago
  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.
  - Dagger2 8mo ago
    Source address selection is usually left to the kernel, so that part should be okay. It'll pick a GUA source for a GUA destination unless you've changed the labels with `ip addrlabel`.