> Le 28 juin 2015 à 22:00, Brian E Carpenter <[email protected]> a > écrit : > > On 29/06/2015 01:09, Pierre Pfister wrote: >> Hello, >> >>> Le 28 juin 2015 à 10:58, Gert Doering <[email protected]> a écrit : >>> >>> Hi, >>> >>> On Sat, Jun 27, 2015 at 11:48:43PM +0200, Pierre Pfister wrote: >>>> Relaxing the « administrator » may be confusing, as Brian said. >>>> So I guess the MUST could become a SHOULD, which imply it requires >>>> implementers to fully understand the drawbacks >>>> of using non-64 prefix lengths. For instance, /127 could be automatically >>>> used (no need for administrator) if a link >>>> is auto-detected as point-to-point. >>> >>> A MUST is perfectly right here. You can't have implementation A decide >>> "let's use a /64 here" while implementation B goes for "/127"… >> >> You actually can have implementations with different prefix length. >> This is handled by the prefix assignment algorithm. > > Yes, you need that ability in the protocol, but it won't work in practice > to pick an oddball like /80 unless all the host stacks on the link can > handle a shorter IID like 48 (whether it's a LAN or a pt2pt). RFC 7421.
Which is why /64 SHOULD be preferred. We also have this: "In any case, a router MUST support a mechanism suitable to distribute addresses from the considered prefix to clients on the link. Otherwise it MUST NOT create or adopt it, i.e. a router assigning an IPv4 prefix MUST support the L-capability and a router assigning an IPv6 prefix not suitable for Stateless Address Autoconfiguration MUST support the H-capability as defined in Section 10 <https://tools.ietf.org/html/draft-ietf-homenet-hncp-06#section-10>. " So a router will not advertise a /80 on a typical link unless it implements stageful DHCPv6. > >> You may have multiple routers with multiple prefix lengths, but one single >> prefix is ultimately chosen and used by all routers connected to the link. > > So will it work if one router on a pt2pt expects to use a /127 and the other > one can only support /64? The current document does not specify how to configure a pt2pt link. This could be specified later really easily, in a backward compatible way. Also, in general, why and how would a router assign a /64 to a pt2pt link ? I mean, considering pt2pt link, we can assume both ends of the link know the nature of the link… and are therefore able to not do weird things such as assigning a /64 on a pt2pt link. - Pierre > > Brian > >> >> - Pierre >> >>> >>> The sentence is also clearly allowing alternatives: if I tell my router >>> "hey, I want to use /127s on point-to-point links", this is "unless >>> configured >>> otherwise by an administrator", so the MUST is not getting in the way then. >>> >>> Gert Doering >>> -- NetMaster >>> -- >>> have you enabled IPv6 on something today...? >>> >>> SpaceNet AG Vorstand: Sebastian v. Bomhard >>> Joseph-Dollinger-Bogen 14 Aufsichtsratsvors.: A. Grundner-Culemann >>> D-80807 Muenchen HRB: 136055 (AG Muenchen) >>> Tel: +49 (0)89/32356-444 USt-IdNr.: DE813185279 >>> >>> _______________________________________________ >>> homenet mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/homenet >> >> _______________________________________________ >> homenet mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/homenet >> . >> > > _______________________________________________ > homenet mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/homenet
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