Re: [Softwires] Proposed Unified Address Mapping for encapsulation and double-translation

[Jacni Qin <[e-mail]>]

hi,

Inline please,

On 10/6/2011 10:37 AM, Rémi Després wrote:
> ...
>
>> 2. Still for the destination address format, I suggest to embed PSID 
>> as well in the lower 64 bits (as in the following).
>
> <--------- 64 ------------>< 8 ><----   32 ----><--- 16 ----><8 >
> +--------------------------+----+---------------+------------+---+
> |     BR subnet prefix     | V  |  IPv4 address | PSID |  0  | L |
> +--------------------------+----+---------------+------------+---+
>
> The reported informal agreement we had in Beijing didn't explicitly 
> cover destination addresses, and I just reported what we said, but 
> this is AFAIK the implicit direction to go to.
> Yet, there is a point to be taken into account:
> - It concerns use cases where IPv6 prefixes are assigned without any 
> relationship with IPv4 prefixes and where different sharing ratios are 
> implicitly expressed by different IPv6 prefix lengths (they aren't the 
> only use cases, but are the only ones where a flat IPv6 routing plan 
> can be used with differentiated sharing ratios).
> - For this, a BR or CE that transmits to a CE destination doesn't know 
> the exact PSID length of this CE. It only knows the maximum possible 
> length of this PSID, but this is enough for the right CE to be reached 
> (ref draft-despres-softwire-4rd-addmapping-01 sec 7.)
>
> Thus, for more generality, the format for a Destination CE would 
> rather be:
>
> <--------- 64 ------------>< 8 ><----   32 ----><--- 16 ----><8 >
> +--------------------------+----+---------------+--------+---+---+
> |     BR subnet prefix     | V  |  IPv4 address |Max PSID| 0 | L |
> +--------------------------+----+---------------+--------+---+---+
>
> If the PSID length is known, then the Max PSID is the exact PSID, but 
> this isn't the only case.
>
I understand the "Max" PSID, based on which there will be no problem 
being routed to the destination. While I'm rethinking of it from the 
implementation perspective, the IID part the IPv6 address destined to a 
given CE should be a fixed value (the same as the IID of the "4rd 
interface" for example). Then the variable "max" PSID derived from dst. 
ports may get a problem.


Cheers,
Jacni