Remi, thanks for the further explanation. let me remove the cleared part and make the message shorter. :P
2011/10/21 Rémi Després <[email protected]> > > > >> (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). >> > > Oops, another bug :-(. > The right formula for ri is: ri = m - (32 - hi) > yeah. :P i didn't discover that. The PSID is WITHIN the /60 (at its end). > to clarify: WITHIN the /60 means within the address block of the /60, not *within the first 60 bits*, (then at its end = starts from 61st bit), right? > > The IPv6 /64 prefix to be used to reach a CE contains: > 1) The Rule IPv6 prefix (that of the rule whose IPv4 prefix matches the > IPv4 destination) > 2) The IPv4 suffix (that part of the IPv4 destination that follows the IPv4 > prefix of the matching rule) > the CE IPv6 prefix = 1) + 2), right? > 3) The PSID (whose length is known iff the matching rule specifies a CE > IPv6-prefix length) > the EA bits = 2) + 3), right? > > 4) If the PSID length is unknown, the "PSID complement" that completes the > Max PSID. > 5) A 0 padding if fields 1 to 4 don't reach 64 bits > > Note 1: If a Domain-IPv6-suffix option is used, the PSID length is > necessarily known, and the PSID complement is then replaced by the Domain > IPv6 suffix found in the matching rule. (ref draft-murakami-softwire-4rd-01. > it seems to me that the draft-murakami-softwire-4rd-01 hasn't explain how do we use the "Domain IPv6 suffix", :( > Note 2: If ordinary CE IPv6 prefixes are /60s, the PSID complement has > typically 4 bits (to fit in the /64). > The only exception is if the sharing ratio needs to exceed 256, so that the > PSID length exceeds 8. Then, the PSID complement of less than 4 bits. > > 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? > > > Yes. > > The only impossibility is if the available IPv4 space is so small that no > sharing ratio can be sufficient for the number of IPv4 shared addresses to > equal the number of ordinary CE IPv6 prefixes. > sure. in this case we can help nothing. > If the above is still unclear (or bugged!), thanks for letting me know. > > Regards, > RD >
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