Re: [pcp] PCP Server Selection - Address Family Selection

[Simon Perreault <[e-mail]>]

Le 2014-04-27 20:52, Dan Wing a écrit :
> 
> On Apr 26, 2014, at 2:37 PM, Sebastian Kiesel <[e-mail]> wrote:
> 
>> On Fri, Apr 25, 2014 at 06:42:53PM -0700, Dan Wing wrote:
>>>
>>> On Apr 25, 2014, at 7:57 AM, Simon Perreault <[e-mail]> wrote:
>>>
>>>> Le 2014-04-25 10:51, Sebastian Kiesel a écrit :
>>>>> draft-ietf-pcp-server-selection-02  says in Section 3:
>>>>>
>>>>>  1.  If the PCP client can use both address families when
>>>>>      communicating to a particular PCP server, the PCP client SHOULD
>>>>>      select the source address of the PCP request to be of the same IP
>>>>>      address family as its requested PCP mapping (i.e., the address
>>>>>      family of the Requested External IP Address).
>>>>>
>>>>>
>>>>> What is the reason for saying it SHOULD use the same familiy as the
>>>>> requested EXTERNAL IP address?  I think it would make more sense to use
>>>>> the same familiy as the INTERNAL address (if there is a difference at
>>>>> all).
>>>>
>>>> +1
>>>>
>>>> I stated this in my review.
>>>
>>> The intent of the wording is to avoid NAT64 (or NAT46) where NAT44 or
>>> no NAT was necessary at all. 
>>
>> reasonable goal, but does text about that belong here?
>>
>> this text is about PCP messages, and I think they should use the
>> same address family as the actual user data flow on their side of
>> the NAT.
> 
> If that avoids IP address family translation, sounds good to me.  Or is there some other value or purpose?

I understand what you want, but the text doesn't get you what you want.
I want something different, but we can both get what we want with
appropriate text.

First, "sending over IPvX" doesn't imply that the internal address is
IPvX, because of THIRD_PARTY. What you want is: "the client SHOULD pick
an internal address of the same family as that of the mapping's external
address."

Second, what I want is to avoid THIRD_PARTY. So that's why you need to
send the request using the chosen internal address as source for the PCP
request. (This is actually stricter than just using the same address
family, in case you have multiple addresses of that address family.)

Summarizing:

"If a PCP client has access to internal addresses of multiple families,
then it SHOULD choose the mapping's internal address such that it is of
the same family as that of the mapping's external address. This is done
to avoid address family translation when possible.

The PCP client SHOULD use the mapping's internal address as source for
the PCP request. This is done to avoid using the THIRD_PARTY option when
possible."

Simon
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