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

[Ole Troan <[e-mail]>]

Remi,

[...]

> 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 |
> +-------------+--------+---+---+----------------+------+-----+---+

putting the IPv4 address / port information at the end of the interface identifier will allow for > /64 support.
what's the L?

you suggest that the first subnet of an allocation should be used for this purpose.
the first subnet is convenient to use for e.g. manual addressing (since it allows the :: short hand).
I do wonder if this has to be provisioned. e.g. some deployments may use the first subnet for the link between
CE and PE. (i.e. a /56 - 1 using the PD exclude option is used).

> 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. 

or rather IEEE?
I am not convinced that "V" is needed.
you could even use the IANA OUI if pretty printing was required.

> 
> (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 |
> +--------------------------+----+---------------+------------+---+

this is a big change for encapsulation, where prior to this encapsulation means sending to a single destination.
if we also allow for a BR subnet prefix of /128 I'm OK with this (I think).

> 
> Note that if double-translation CEs are notified to use U instead of V, the last octet becomes 0 per RFC  6052.

how would a CE know if it was single or double translating?

e.g we could do:

<--------- 64 ------------><--- 24 ------><----- 32 -------><--8 >
+-------------+--------+---+--------------------+------+-----+---+
| IPv6 prefix |CE index| S | 00-00-5E    |  IPv4 address  | PSID |
+-------------+--------+---+---+----------------+------+-----+---+

we also need to handle the case where IPv6 prefix + CE index > 64. I suggest we then just put as much as the interface identifier that will fit.

cheers,
Ole