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Comment by Hobadee | Hacker News Reader

> > - My ISP gives me a /64, what am I supposed to do with that anyways?

> What are you supposed to do with a /8? Do you have several million computers?

Except you can subnet an IPv4 /8. You can't subnet an IPv6 /64. For whatever stupid reason, and despite having 18 quintillion available addresses in a /64, you can't actually do anything useful with it other than yeet a bunch of devices on the same LAN segment.

(At least on pfSense, and when I looked into it some, that's apparently IPv6 design for some reason)

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Your ISP gives you a IPv4 /32 which you don’t have a prayer of subnetting, you have to NAT.

With a IPv6 /64 you can (1) NAT, or (2) better, subnet it and use DHCPv6.

The only thing significant about /64 is that’s the smallest unit for SLAAC.

Android only supports slaac.

Strangely it supports DHCPv6 as a server but not as a client.

It's not strange. It's Google's plan to push ISPs into supporting SLAAC and giving you at least /64 instead of giving you a single /128 address.

It is not a bad thing actually.

> The only thing significant about /64 is that’s the smallest unit for SLAAC.

...which means you can't subnet it because you have to assume SLAAC might happen since that's the only thing ipv6 requires. Ergo, an ISP only giving you a /64 means you have to nat if you want subnets, and if you have to nat why wouldn't you use ipv4 instead where it's so much simpler?

I haven't looked at pfsense UI, but you can happily hand out a prefix to a device, which can then hand out its own prefixes. I do it with my k8s clusters, which means the node themseves have enough IPs addresses to launch their own routable k8s clusters.

Thats why its recommended that ISPs give /56 by default (and up to /48 if requested). This way you can do plenty of effortless subnetting. If your ISP is only giving you /64 even after you requested a larger subnet he is doing IPv6 WRONG.

You can totally subnet from /64, you just can't use SLAAC. The packet header doesn't care about your address allocation scheme.

At the same time SLAAC is the reason your ISP doesn't give you a /128.

Of course you can subnet ipv6, in fact I run several ipv6 subnets at home. You have to delegate a different prefix to each subnet.

They said that you can't subnet a /64, not that you can't subnet in IPv6. And while technically you can subnet even a /64, it's not supported by SLAAC, which means that, for example, you can't get an Android phone to work with auto-assigned addresses in a /80 IPv6 network.

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