Ole,
I just discovered that my previous email didn't have, by mistake, the Softwire
ML as destination.
Since the subject is clearly of common interest, and has nothing secret, I
correct now the mistake.
Comments in line.
2012-03-06 21:28, Ole Trøan:
> Remi,
>
>> Trying to figure out what the MAP port-set algorithm is, I was confused:
>> (a) According to MAP dhcp-option-02, parameters are AFAIK:
>> - the PSID length (implicit, derived from ea-len and prefix4-len)
>> - excluded-ports
>> - offset
>> (b) According to MAP address-and-port-03 parameters are:
>> - Sharing ratio R
>> - Maximum number of contiguous ports M
>> - an apparently fixed set of excluded ports (0-4095)
>> Could you clarify what is proposed?
>
> sharing ratio can be derived from the PSID length. M can be derived from 16 -
> offset - PSID length.
> PSID length is derived from EA-bits length.
> the only specific to the algorithm that may be provisioned (it is optional)
> is the offset.
> and in theory the excluded ports.
"in theory" doesn't really clarify.
Is it a parameter?
- If yes, the MAP-address-and-port draft needs AFAIK an update
- If no, the MAP-dhcp-02 draft needs AFAIK to be modified
If I missed something, thanks for an explanation.
> my personal view, is that we should drop the optional parameters too.
Sees (*) below.
> the algorithm would still be the same though.
See (**) below
>> 2.
>> Detailed MAP examples you give have excluded ports 0-4095, offset=4, and no
>> M.
>> This is exactly what 4rd has without needing any parameter, and with a
>> trivial algorithm instead of the somewhat brain-teasing algorithm copied
>> below.
>> Could you clarify which use cases you see that would justify such complexity?
(*) So, you don't personally see any use case than would justify a
PSID-algorithm parameter.
We both agree on this.
> I think you misunderstand. what you see below is the 4rd algorithm.
??? (see below)
> please write an implementation of your version of the algorithm, and see if
> you don't end up with pretty much the same as is shown below.
(**) 4rd derives a port set from a PSID as shown in the picture below. I would
implement it with masks and shifts rather than with multiplications and
divisions and, in any case, without needing to think of any "Maximum number of
contiguous ports" and a "Sharing ratio".
: 4 :
+---+----+---------+
Ports in the CE port set |> 0|PSID|any value|
+---+----+---------+
: 16 :
Cheers,
RD
>
>> Copied of your section 4.1:
>> The port number (P) of a given PSID (K) is composed of: P = R * M * j + M *
>> K + i Where:
>> * PSID: K = 0 to R - 1
>> * Port range index: j = (4096 / M) / R to ((65536 / M) / R) - 1, if the
>> well-known port numbers (0 - 4096) are excluded.
>> * Contiguous Port index: i = 0 to M - 1"
>
> cheers,
> Ole
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