Once upon a time, Kenneth Porter <shiva at sewingwitch.com> said: > --On Tuesday, April 28, 2020 10:16 PM -0500 Chris Adams > <linux at cmadams.net> wrote: > >And frankly, giving you a /56 is pretty crappy, since ARIN rules say to > >give every site a /48. I'd only do a /56 for a home connection prefix > >delegation. But, that's AT&T! :) > > I'd just read about that when researching this. Maybe they decided > that since we only have about a dozen people at our site, we won't > have a lot of subnets. What do small offices DO with 256 public > subnets, anyway? I suppose eventually we'll have an IoT subnet on > every person. The idea with IPv6 is not to even necessarily think about it in terms of direct numbers, but in layers. It is not uncommon to have several layers of routers, firewalls, guest wifi networks, etc., and each layer should request a prefix delegation from its parent. So rather than 256 subnets, think about it as 8 layers (at most... but if a layer has more than 2 children, you have fewer layers available). So for example, if your Internet gateway has a desktop firewall, a guest wifi, a public DMZ, and a development lab gateway connected, and you want to allow for more things at that layer, there's 3 of your 8 bits in a /56. If the dev lab needs to fan out more, and maybe your public DMZ needs to break up for production and QA-testing networks, and you add a VPN concentrator to the desktop network... you can go through those bits fast. In IPv4, people would just NAT the crap out of everything, having to tunnel from one NATted network to another, making life really difficult. The plan is no NAT in IPv6, so allow for all potential allocations up front. Also, allocations should be larger than necessary and sparse, so that you never need another allocation (even if you grow to 1000 employees and multiple buildings on a campus). This is to hopefully prevent routing tables from exploding like IPv4 did (and also to avoid you having to renumber everything just to stay in a single block). -- Chris Adams <linux at cmadams.net>