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

[Qiong <[e-mail]>]

Hi, Remi,

Thanks for your effort. I think this is a big progress after the Interim
meeting, and this unified address format is quite clear now. Here, I have
two comments after a quick review. And I will get back to you if I have more
comments later.

1. With regard to destination address format, if I understand correctly, it
only covers hub&spoke model with a default "BR subnet prefix". Are you
intended to propose another format for mesh one ? Or just cite the "Source
address format" as the destination address in MESH situation. I think it
would be better to declare it separately for "H&S" and "MESH". This would be
more clearer for readers to understand different situations.

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 |
+--------------------------+----+---------------+------------+---+

This would make it easier for in-the-middle systems(e.g. BNG) to do prefix
mapping without packet decapsulation. And this is quite similar to the
source address format. What do you think of it?


Best wishes

Qiong


On Tue, Oct 4, 2011 at 12:22 PM, Rémi Després <[e-mail]>wrote:

> Hi all,
>
> 1.
> Here is a unified Address Mapping, for both encapsulation and
> double-translation approaches, that is PROPOSED for IPv4 residual deployment
> across IPv6-only routing domains.
>
> It results from an informal meeting among participants having different
> preferences between double-translation and encapsulation solutions (Xing Li,
> Congxiao Bao, Wojciech Dec, myself, at the end of the Beijing meeting).
>
> The idea is to have a common format that is good for both types of
> solutions.
> In particular:
> - It enriches Double translation by introducing a deterministic way to
> distinguish a translated IPv4 packet from a native IPv6 packet.
> - It enriches Encapsulation by expressing, in clear format within an IPv6
> address, an IPv4 address, an IPv4 prefix, or an IPv4 address + port-set ID.
>
>
> 2.
> (a)
> The IPv6 Source address of an IPv4 packet from a CE is:
>
> a1- If the CE has an exclusive or shared IPv4 address:
>
> <--------- 64 ------------><8 ><------ L >= 32 -------><48-L><8 >
> +-------------+--------+---+---+----------------+------+-----+---+
> | IPv6 prefix |CE index| 0 | V |  IPv4 address  | PSID |  0  | L |
> +-------------+--------+---+---+----------------+------+-----+---+
>
> a2- If the CE has an IPv4 prefix:
>
> <--------- 64 ------------><8 ><-- L < 32 --><--- 48-L -----><8 >
> +-------------+--------+---+---+-------------+---------------+---+
> | IPv6 prefix |CE index| 0 | V | IPv4 prefix |         0     | L |
> +-------------+--------+---+---+-------------+---------------+---+
>
> (b)
> V is the mark that characterizes IPv6 packets that are in reality IPv4
> packets.
> Its value differs from any permitted value of this octet in IPv6 IIDs  (ref
> RFC 4291).
>
> It is understood that, if double Translation coexists with single
> translation, concerned ISPs may notify their CEs to use the U octet of RFC
> 6052 instead of V.
>
> An unambiguous mark is fortunately possible because currently permitted
> IIDs have in their first octet either bit6 = 0 (the "u" bit"), or bit6 = 1
> and bit7= 0 (the "g" bit).
> With V having "u" = 1 (signifying Universal scope) AND "g" = 1, distinction
> is therefore deterministic.
>
> The proposed V is = 00000011.
> (With other values of this octet, other IID formats can be defined in case
> some would be useful in the future.)
>
> Note that, if and when a consensus is reached in Softwire, an extension of
> RFC 4291 will have to be submitted to 6MAN.
>
> (c)
> A Destination address from a CE to the outside IPv4 Internet is:
> <--------- 64 ------------>< 8 ><----   32 ----><--- 16 ----><8 >
> +--------------------------+----+---------------+------------+---+
> |     BR subnet prefix     | V  |  IPv4 address |      0     |32 |
> +--------------------------+----+---------------+------------+---+
>
> Note that if double-translation CEs are notified to use U instead of V, the
> last octet becomes 0 per RFC  6052.
>
>
> 3.
> All comments are most welcome.
>
> Kind regards to all,
> RD
>
>
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