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by hampereddustbin 1321 days ago
Doesen't /64 mean that you can't create additional subnets within your ISP given range? I thought /56 was the smallest allocation an ISP could make for a residential allocation.

I think it's great that the smallest subnet size is designed to be as large as to never run out of addresses in any conceivable application, no more wasting precious time manually assigning addresses and thinking about subnet economics
3 comments
aaronax 1321 days ago
> Doesen't /64 mean that you can't create additional subnets within your ISP given range?

Effectively yes.

> I thought /56 was the smallest allocation an ISP could make for a residential allocation.

They can and often do make /64 allocations. There is an RFC (I think, might just be RIPE guidance or something) that recommends that ISPs issue larger to each customer. Many don't (as it is just a recommendation). Ideally they would allow a customer's router to request a larger allocation like /60 or /56 via a prefix delegation message.

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jeroenhd 1321 days ago
/56 is the smallest they're supposed to allocate for customers, but I've read stories about ISPs providing people with /128s on their CPEs...

A /64 can actually cause problems if you're chaining routers together. In IPv4 that'd give you double NAT which is obviously terrible and not recommended, but in IPv6 that's a fine use case that shouldn't cause any trouble as long as you have the ability to create sufficient subnets. With a /64, you're stuck doing weird stuff with DHCPv6 to get the subnets to work regardless.

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aidenn0 1321 days ago
You don't need double-NAT with ipv4 to chain routers together, just route between different private-allocation subnets. I was running a setup like that to get ethernet access to a part of the house via wifi. Changed it for ipv6 though because my isp only gives me a /64
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tsimionescu 1321 days ago
In previous threads, there were even people saying their ISPs provide them a single IPv6 address, so essentially a /128.
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staringback 1321 days ago
They may be misunderstanding how their ISP provides IPv6 address space. For example my Comcast connection assigns a single /128 to the router, then a bunch of /64s to each subnet I have set up.
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