Hacker News Reader

Comment by 4ad | Hacker News Reader

> Their default is to give a /60, which seems appropriately overkill.

A /60 is pathetically small, with SLAAC you have 16 (!!) subnets for your whole network. With people having multiple computers and multiple phones, this is not enough even for a normal household of 3 people. If you are a IT person, with multiple computers and VMs, forget it.

The recommended size of block that every ISP should give is /48 (RFC 6177). Good ISPs will give you a /48, some lesser ISPs will give you a /56. Comcast and crappy ISPs will give you a /60.

View on HN

How does a household with 3 people need 14 subnets?

I agree a /60 is stingy, but "not enough even for a normal household of 3 people" sounds like massive hyperbole. Even as a tech enthusiast filling that would be some work, unless you insist I use a /64 for point-to-point links.

> Even as a tech enthusiast filling that would be some work

Have you ever used VMs on a laptop? How many virtual networks do you need? Only one? With only one you only need one extra bit bit for routing, so you could give a /63 instead of a /64 to your laptop, except that IPv6 allocation is supposed to be done in nibbles (and you need to overprovison anyway, what if tomorrow you need two networks?), so the next logical step is a /60, which means your ISP should give you at least a /56. Personally, I use much more than one virtual network on my laptops, so I would need a /60 anyway (if I want to keep all the nice properties of IPv6, that is).

As long as you want to keep everything nice with IPv6, the block you need is /64-(4*n), where n is the level of routing you plan to do.

> unless you insist I use a /64 for point-to-point links.

Each p2p link on IPv6 uses a /64 (even though it's only assigned an /127).

> How does a household with 3 people need 14 subnets?

In the IoT era (where S stands for security), if you don't put each IoT device in its own VLAN, you are in for a surprise.

> Have you ever used VMs on a laptop? How many virtual networks do you need?

Very few, to the point of "if it's more than one, the other ones aren't intended be reachable and thus don't need public space".

> Each p2p link on IPv6 uses a /64 (even though it's only assigned an /127).

No, it doesn't, since my routers don't need to do SLAAC between each other, but can happily live with static IPs.

> In the IoT era (where S stands for security), if you don't put each IoT device in its own VLAN, you are in for a surprise.

Never felt the need to put each device in it's own subnet, sensible firewalling seems enough. I tend to avoid devices that really want to talk to the internet though, so most of the time it's "you don't get to talk to the internet"-subnet. But ok, if you love connected stuff and want to split it in very fine ways, that'd be a bunch of subnets.

So yes, as I said /56 would be nice and should be the default but /60 is likely to be enough for the vast majority of users.

Seems pretty huge to me. I could give just about every person on the planet (call it 8 billion or 2^33) each their own personal IPv4 (2^32) worth of IPs.

I've got a larger then normal home router with 6 ports. I can have a /64 for each, and still have a bunch left over if I want to split up wireless into more secure, medium secure, less secure, and least secure networks.

I'm all for more address space, but I'm at a loss as to why a normal even a sophisticated home user needs more than a /60.

I wouldn't turn down a /48, but realistically I've got 30 or so IPs in use. Sure recently I added an IP for a wristwatch, TV, and a stereo. Clearly cheaper devices are getting Wifi. It's becoming more common in appliances, thermostats, door locks, electrical outlets, light bulbs etc. But 2^64 pennies is quite a bit, and I doubt anything will be consuming more than one IP per $0.01 of cost anytime soon.

That's not how IPv6 works. In IPv6 the lower 64 bits are essentially random, and the most significant 64 bits are used for routing. Each additional level of routing must use up one bit, except because of over-provisioning concerns, and to keep everything nice, you are supposed to use a nibble (4 bits).

A /64 can't be subnetted any more (one host, NO VMs!).

A /60 can support one level of extra routing.

A /56 can support two levels of extra routing.

If you plan to run VMs on your laptop, you need a /60 on your laptop, which means you need a /56 from your ISP. If you want to keep everything nice and future proof, that is, if you want to fuck up with special configurations, you can use your /60 from your ISP, and give a /62 to your laptop, then each laptop can have 4 networks for VMs. But that is limiting and a PITA to set-up.

> A /64 can't be subnetted any more (one host, NO VMs!).

Why not directly bind all VMs to laptop's NIC? This way, they can get IP from the same /64 subnet. On firewall, only enable public access to those VMs that are needed.

I do have a home lab, but every VM is directly bridged to NIC and gets its IP from home router. So a single /64 is sufficient for me.

Sometimes it's fine to do that, other times it isn't. If you plan to test network topology, firewalls, you can't do that. If you plan to run untrusted VMs, you also can't do that.

I'd use a unique local address network (/32) for this

https://tools.ietf.org/html/rfc4193

That's fine for some scenarios, but in general for my use cases, I wouldn't, because most often I want my VMs to be accessible from the Internet.

At this point I'd argue your case is a bit special and you may need special arrangements. If it is that critical for you to have a gazillion of IoT devices and untrusted VMs accessible from the internet via IPv6, get a /48 tunnel from he.net

To be fair, his special case just works on IPv4, but not on IPv6. So it’s a regression in functionality without the right prefix size.

Comcast business users can get a /56 by requesting it in their dhcpv6 settings.

I have Business. I request a /56. It gives me a /60. I try to partition that out into subnets, but prefix-delegation (PD) fails at that point.

Sounds like a router configuration issue. I have no issue getting a /56 and handing out /64's on a Comcast Business line.

Do you have a static v4 block as well?

On a business account you get a /56 and on MetroE you get a /48 or more. Given the huge majority of consumers only ever use a /64, giving a /60 seems reasonable.

Reply on news.ycombinator.com