On 08/10/2014 20:50, Pierre Pfister wrote: > Hello Brian > > Please find my answer inline. > > Le 8 oct. 2014 à 02:32, Brian E Carpenter <brian.e.carpen...@gmail.com> a > écrit : > >> On 08/10/2014 12:14, James Woodyatt wrote: >> >> (quoting draft-ietf-homenet-prefix-assignment-00) >> >>> prefix. If no ULA prefix can be found in stable storage, it MUST be >>> randomly generated, or generated from hardware specific values. >> That sentence is not OK. It should be: >> >> If no ULA prefix can be found in stable storage, it MUST be generated >> as specified in [RFC4193]. > > The point was to have a pseudo-random algorithm that always generates the > same ULA. > Stable storage can be used, but on most crappy home routers, writing on the > SSD too much will kill it in a few thousands writes.
There is nothing in RFC 4193 that prevents saving the generated ULA in stable storage for future use; so I think you need to be clearer that when a ULA is generated, it SHOULD be stored for future use (until the next factory reset). I don't see why that generates more than a very few writes to SSD. > [RFC4193] states: > 3.2.1. Locally Assigned Global IDs > > Locally assigned Global IDs MUST be generated with a pseudo-random > algorithm consistent with [RANDOM]. > > If remembering the ULA prefix and using it again and again (using stable > storage) is OK, I don’t see why we would need cryptographic pseudo-randomness > here. > And actually that’s even worse. Why would a cryptographic pseudo-random > function would be used with a *known* seed. > The ULA doesn’t need to be secret. It just needs to be random enough to avoid > collisions. Well, yes, but randomness is randomness, i.e. all values are equally likely. It's really the same thing. I think the assumption was that any box capable of generating a ULA would already have something better than rand() built in for other reasons. > My point here is that if we conform to RFC4193, we lose the stability of the > generated ULA, and IMHO we win nothing. But if you deviate from the standard you need to say so explicitly. "This procedure deviates from [RFC4193] because...". > Correct me if I’m wrong, but I think using hardware specific values as seed > is perfectly fine with the collision-avoidance requirement. I would expect so, and I'm not against what you propose, it just needs to be clearly documented. Brian > Cheers, > > Pierre > >>> The requirements keywords in this section make for a pretty serious interop >>> clash with Thread networks <http://threadgroup.org/>, which generate their >>> own ULA prefix based on a method defined by its current conventions. >> I sincerely hope that method conforms to RFC4193. >> >> Brian >> >> _______________________________________________ >> homenet mailing list >> homenet@ietf.org >> https://www.ietf.org/mailman/listinfo/homenet > > _______________________________________________ homenet mailing list homenet@ietf.org https://www.ietf.org/mailman/listinfo/homenet