hi Remi, thanks a lot for the reply! it is very helpful and my latest understanding almost approach it. but still some minor clarifications. 2011/10/20 Rémi Després <[email protected]>
> Hi Maoke, > > Thank you for your questions concerning relationships between IPv6 and IPv4 > addressing plans. > > Here are address-planning steps that illustrate how an IPv6 addressing plan > can be kept independent from IPv4 prefixes used for IPv4 residual > deployment, even if CEs must be able to have different sharing ratios. > > (A) IPv6 considerations > (A1) Determine the maximum number N of CEs you want to support, a power of > 2 (N = 2 ^ n). > (A2) Choose the length x of IPv6 prefixes you want to assign to ordinary > customers (e.g. x = 60) > (A2) Multiply M by a margin coefficient K, a power of two (K = 2 ^ k), to > take into account that: > > here the M should be a typo of "N", right? ;-) > > - Some privileged customers may be assigned IPv6 prefixes of length x', > shorter than x, to have larger addressing spaces than ordinary customers, > both in IPv6 and IPv4. > - Due to the hierarchy of routable prefixes, many theoretically > delegatable prefixes may not be actually delegatable (ref: host density > ratio of RFC 3194). > > (B) IPv4 considerations > (B1) List all (non overlapping) IPv4 prefixes Hi that are available for > IPv4 residual deployment. > (B2) Take enough of them, among the shortest ones, to get a total space > whose size M is a power of two (M = 2 ^ m), and includes a good proportion > of the available IPv4 space (ref > www.ietf.org/mail-archive/web/softwires/current/msg02261.html). > (B3) For each IPv4 prefix Hi of length hi, choose a "Rule index" Ri of > length ri = m - hi. All these indexes must be non overlapping prefixes (e.g. > 0, 10, 110, 111 for one /10, one /11, and two /12). > > (C) After (A) and (B) > (C1) Derive the length c of the "Common prefix" C that will appear at the > beginning of all delegatable prefixes (c = n + k - m) > (C2) Take for C any prefix of length c that starts with a RIR-allocated > IPv6 prefix > (C3) For each IPv4 prefix Hi, make a rule in which it is the IPv4 prefix, > and in which the IPv6 prefix is the Common prefix C followed by the Rule > index Ri. > > I hope this can work on your favorite example(s). > If not, please let me know. > it seems you didn't mention the PSID part. my understanding is, after the above, when we have the, e.g., /60, the PSID is attached after the /60. then the CE delegated prefix (including IPv4 address suffix and PSID) may have different lengths if the sharing ratio is variant for different shared IPv4 addresses. but the c + m (or n + k, or x (right?)) , including the common prefix and the ipv4-address-related bits, is a constant for every CE-delegated network in the domain, right? on the other hand, there is a limitation. if c + m > 64, the above address planning is not deployable, but with our effort of maximum compression, we believe the undeployable case rarely happens for normal providers, right? > Note that this is by no means to say that all ISPs should plan addresses > this way (i.e. with a relationship between lengths of CE IPv6 prefixes and > sharing ratios). It is just to show that this is workable. > > sure. but i believe this will helps operators very much, considering up to now no operators have experienced that. thanks, maoke > > Regards, > RD > >
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