On Feb 25, 2013, at 16:28 , Lorenzo Colitti <lore...@google.com> wrote: > On Tue, Feb 26, 2013 at 4:21 AM, james woodyatt <j...@apple.com> wrote: >> As a result, it means that Automatic Prefix Management here is basically >> unable to do it statelessly, i.e. by randomly generating subnet numbers from >> an identifier space of conventional size and testing for collision before >> using them. > > Why do you say this? Assuming the ISP(s) providing service to the home assign > enough space to number all the links (e.g., /60, /56, or /48), then what's > the problem?
p1. I don't believe it's reasonable to assume that service providers will always provide a short enough prefix to number all the links in a subscriber's network, or that those that currently do will continue to do so into the foreseeable future, or that they will even give notice prior to reducing the space delegated to a subscriber. p2. In a decent sized subscriber network, with several subnets in place, a /56 delegation means a small but significant changes that a randomly selected subnet identifier will collide with an existing one, whenever a router joins the network. With a /60, the odds climb quite a bit, and in some networks it will be 15/16. (Do not make the mistake of assuming that router joins and leaves will be infrequent events. Plan for them happening several times per second, or you will be sorry later.) p3. All this pain can be traded away for the reasonably well-understood pain of NAT66 and a single ULA prefix with a constant 16-bit subnet identifier space, where collisions will be rare and stateless prefix autoconfiguration will settle quickly basically every time. I personally don't think that's a good trade, but if routed home networks are ever to become the normal setup, then I'm very skeptical that my opinion will turn out to be the majority one. I think if we want to avoid the temptation of subscribers to deploy NAT66 to preserve the stability of their 16-bit subnet identifier space in the face of service providers "enhancing their choices" with a variety of plans with varying policies for prefix delegation, then we have to do it with a stateful subnet manager in the network, near the border gateways. -- james woodyatt <j...@apple.com> core os networking _______________________________________________ homenet mailing list homenet@ietf.org https://www.ietf.org/mailman/listinfo/homenet
