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Could you give a brief overview of your current understanding? I'm curious as to why /60 would be too limited, and how it's different from IPv4.

Probably because /64 is the smallest recommended subnet size, and a /60 has “only” 16 /64 subnets within it.

[not OP, but hey…] There’s no need for DHCP with IPv6. Clients choose the last 64 bits of an address randomly. The address space is huge — zero probability of a duplicate address.

The first 64 bits therefore identify the network. If your ISP routes a /60 to you then you get to split that into 16x /64s.

That’s probably fine, but the IETF recommendation is to dish out a /56 to small sites and give them a /48 if they ask for it. ISPs usually have multiple /32s at their disposal.

It’s not about number of available addresses or networks. The joy of IPv6 is the addresses are so wide you can bring back hierarchical addressing. No internal routing chicanery is needed.

If your site has 64 buildings then a /56 lets you assign a /62 to each, with 4x VLANs in each building eg for printers, guest net, phones, lighting, admin, with even a subnet for each business function in the building.

Some way of automatically propagating that network prefix to anything connected to the network would be nice. Otherwise we're just stuck punching in IP addresses like barbarians.

Not sure what you mean, but there's definitely no need to type addresses anywhere.

Router Advertisements propagate the subnet information (prefix, dns server, etc.) to clients in the network. Prefix delegation allows downstream routers to request subnets from upstream routers. MDNS lets network devices announce their services to the subnet.

RA: router advertisements.

The good riddance part of IPv4 DHCP is the server maintained state. The broadcast-config thing is still there. RADVD is the standard Linux daemon for this.

> The address space is huge — zero probability of a duplicate address.

Not necessarily, there could be a flawed SLAAC implementation where the programmer just hard coded the default address after getting the PD. Or other some such silliness.

Yes it breaks spec. But there's enough devices out there that break the link local configuration spec that I would not be surprised one but if someone pushed out a broken implementation of SLAAC on a commercial product.

DAD at the other end kills bad actors like this fast. But if the implementation at both ends is broken…?

IPv6 has Stateless Address Auto-Configuration (SLAAC) as preferred method for address assignment. This allows clients to generate addresses for themselves as needed. For that to work efficiently, the address space needs to be sufficiently large that collisions are unlikely even in larger networks. Because of that, it mandates a subnet size of /64.

More generally, a big difference in v6 is that you no longer have to plan subnet sizes at all. Whereas previously you'd carefully choose the next available address to minimize address waste, with v6 you can just assign the addresses in whatever way makes sense to you.

The idea is that there's SO much address space -- you should never need to consider a question like: "is /60 to /64 enough for all of my subnets?" when planning your network. Subnets should be created because they make sense from an organizational point of view. The amount of available bits shouldn't be a practical consideration.

Also, remember, NAT is highly discouraged, so you'll (maybe) eat up another subnet if you run something like Minikube on a laptop.

How useful would that book (IPv6 Address Planning) be to someone not working specifically in networking/ops? I like developing applications and i manage, of course, my home network.

I'd love a book that gives me everything i need to know about IPv6. From justifications, to things to know when working with it, implementing it, using it in my local network, etc.

I don't perhaps need or care to learn it at a super low level, but i do want a complete understanding of it for my specific use cases. Applications and home networks, i imagine. For a novice in networks, to be clear.

Thoughts?

I would guess that the first two chapters would be useful.

Honestly, if your first thought isn't "oh wow, I would love to learn how to plan out IPv6 networks", it might not be worthwhile.

For home you probably care about SLAAC, PD, the standard subnet size of /64, and possibly the Link Local differences (more out of curiosity of what those addresses show up on your machines for than needing to know to do anything with it). Also DNS is going to have AAAA records instead of A records and reverse lookups use a different zone, the changes in DNS are pretty 1:1 translational for admins though. If you want to go full on v6 you'll want to read about NAT64 so you can still reach the v4 internet from your v6 only home network. Also take a look at http://shouldiblockicmp.com/ even if you don't go down the path of v6.

For applications programming you'll want to have a feel for the above, IPv4-mapped IPv6 addresses, and review link local again to in particular note how to encode the interface in a socket call (useful for configurationless cluster communication).

Most every other detail of IPv6 changes should only matter to those that write networking stacks or make routers.

For all of the above info I'd recommend just reading the Wikipedia article on IPv6. Most of these are straightforward wrote memorization of best practices or background reasoning things so it's not "read a book" worthy if you're not trying to do this for a living IMO (coming from someone who does networking for a living).

They should have had either a smaller scope / simpler extension to IPv4 with a better backwards compat story for IPv6 only clients (some have since shown up a bit).

Or really done the reinvent - there were some interesting ideas especially for folks with lots of link handoffs (ie cell phones driving down a road etc) - can't find the write-up quickly.

Do you mean Mobile IP? https://en.wikipedia.org/wiki/Mobile_IP (part of IPv6)

I understand ISPs giving people subnets because there's an expectation that you'll be using a router. Each of your devices will have a public IPv6 address, obviating the need for NATs and CGNATs. That's neat, and that enables you to do all sorts of things like reliable p2p communication and servers.

But what doesn't make much sense for me is when you're given a subnet many IPv4 address spaces worth addresses on a single network interface on something like a server. Sure you could use that for a VPN, and I did set one up like that, but are there any more use cases? Surely there must be a good explanation why everyone is doing that?