Re: [Softwires] 4rd-addmapping - Possible independence of the IPv6 addressing plan from IPv4 prefixes

[Maoke <[e-mail]>]

Remi,

thanks for the further explanation. let me remove the cleared part and make
the message shorter. :P

2011/10/21 Rémi Després <[e-mail]>

>
>
>
>>   (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
>