I have to say the hierarchical assignment is a such great way to waste address space or prefix bit. I cannot real see much benefits or use cases of it. Why may home site 3 subordinate routers? How many subnets or devices may a /48 prefix serve in this model?
Cheers, Sheng On 3 June 2013 00:39, Owen DeLong <o...@delong.com> wrote: > > On Jun 2, 2013, at 11:10 AM, Ted Lemon <ted.le...@nominum.com> wrote: > > On Jun 2, 2013, at 11:59 AM, Owen DeLong <o...@delong.com> wrote: > > You are assuming that all of the subordinate routers will act as DHCP > relays rather than doing PD. > That is certainly one possible solution, but, not necessarily ideal in > all cases. > In cases where the subordinate routers should receive delegations and > perform their own PD for their subordinate routers, having a larger bit > field can be useful for greater flexibility. > > > No, there is no use case where this is better than doing the delegations > from the router that received the initial delegation (since we're > apparently just arguing by vigorous assertion). > > > We can agree to disagree. > > One example that comes to mind is if I want greater control and I want my > most capable router with the greatest configuration flexibility to be in > charge of the addressing scheme, but, it is not the router that interfaces > with my ISP. > > Thus, providing 16 bits to the end site is, IMHO, worth while. > > > And hence, this conclusion is not supported. > > You are welcome, of course, to contradict me by stating such a use case, > but bear in mind that when you delegate prefixes for further > sub-delegation, topology changes in the homenet become impossible. So > your use case for doing this would have to enable some pretty awesome > functionality before it would be worth doing. Also make sure you think > about how it would work during a renumbering event, with sub-delegations > and sub-sub-delegations all having different lifetimes. > > > Actually, the need for the larger bit field is precisely to allow topology > changes in said deployment scenario. If the top level router hands out, for > example, /50s to its 3 subordinate routers, the subordinate routers can > support a number of different topologies without requiring any changes at > the top-level router. Additionally, a fourth subordinate router can be > added with its own underlying topology supported. > > OTOH, if there are more than 3 subordinate routers, the top level router > can delegate /51s. True, this would complicate the change from 3 to more > than 3 subordinate routers at the top level somewhat. > > (I've got nothing against delegating /48's to the home, but the reason > we did that was to maintain flexibility, not because we really expect a > typical homenet to have 65,536 subnets. At least for most reasonable > values of "we.") > > > You just said exactly what I said to begin with… It's to have a bit field > wide enough to allow flexibility in the automation of the hierarchical > assignments, not to create 65K subnets. I never asserted it was because we > needed 65K subnets. > > Owen > > > _______________________________________________ > v6ops mailing list > v6...@ietf.org > https://www.ietf.org/mailman/listinfo/v6ops > > -- Sheng Jiang 蒋胜
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