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Comment by tsimionescu | Hacker News Reader

The only reason for that "rule" is SLAAC.

I think SLAAC's /64 limit functions as a "trojan horse" forcing ISPs to give everyone at least 64 bits of address space. Most would allocate /112-/128 per customer if it were slightly easier.

Designing the internet with lots of unused space at the edges will probably be useful in 100 years.

Regardless of the /64 limit, I expect DHCPv6 will win out in the consumer side (with ISPs giving customers pre-configured wifi routers with DHCPv6 already configured). SLAAC is both very complicated, and its privacy extensions are anyway not something ISPs have been friendly to even if it weren't such an extra hassle.

> and its privacy extensions are anyway not something ISPs have been friendly to

That is an argument for forcing ISPs to support SLAAC, so it's difficult to bill a customer based on the number of devices in their home. ISP-friendly often means user-hostile.

If ISPs can deploy device-counting DHCPv6, then router manufacturers will respond with IPv6 NAT, and then the IPv6 landscape will be as shitty as IPv4.

Device counting has always been possible with IPv4 routers, and yet I don't know of a single ISP which does this.

To be clear, I'm talking of ISP-provided (usually wifi) routers, which at least in my country are extremely common. Those could receive an IPv6 prefix and do DHCPv6 inside your own network.

The concept of an IPv4 NAT router exists today because people in the '90s wanted to connect multiple devices without permission from their ISP. SLAAC lets you extend a network without permission using ND Proxy, whereas DHCPv6 IA_NA can only be extended using NAT.

So I think SLAAC is good because ND Proxy is less evil than NAT.

> whereas DHCPv6 IA_NA can only be extended using NAT.

Pedantically, it doesn’t force that but it can, right?

Actually it's primarily due to NDP and EUI-64. Eliminating ARP is a very good thing for reasons of scalability, reliability and security.

NDP doesn't impose any restrictions on IP addresses, it uses special prefixes anyway.

EUI-64 is a part of SLAAC, not NDP.

Finally, NDP is not really any more secure at least than ARP (at least not if you don't implement SEND as well, which I'm not sure if anyone does, at least in consumer networks). Not sure about reliability or scalability either.

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