Re: ULA scope [draft-ietf-6man-rfc3484-revise-05.txt]

Arifumi Matsumoto <arifumi@nttv6.net> Fri, 16 March 2012 10:31 UTC

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Subject: Re: ULA scope [draft-ietf-6man-rfc3484-revise-05.txt]
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From: Arifumi Matsumoto <arifumi@nttv6.net>
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Date: Fri, 16 Mar 2012 19:30:07 +0900
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To: Dave Thaler <dthaler@microsoft.com>
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Dave,

On 2012/03/01, at 11:20, Dave Thaler wrote:

>> -----Original Message-----
>> From: Arifumi Matsumoto [mailto:arifumi@nttv6.net]
>> Sent: Thursday, February 23, 2012 10:14 PM
>> To: Brian E Carpenter
>> Cc: Dave Thaler; Chris Grundemann; ipv6@ietf.org; Brian Haberman; Bob
>> Hinden
>> Subject: Re: ULA scope [draft-ietf-6man-rfc3484-revise-05.txt]
>> 
>> Dave,
>> 
>> in Example section of draft-ietf-6man-rfc3484bis-00.txt, I found the response to
>> this issue of ULA scope.
>> 
>> 10.6.  Configuring ULA Preference
>> ...
>>   Since ULAs are defined to have a /48 site prefix, an implementation
>>   might choose to add such a row automatically on a machine with a ULA.
>> 
>>   It is also worth noting that ULAs are assigned global scope.  As
>>   such, the existence of one or more rows in the prefix policy table is
>>   important so that source address selection does not choose a ULA
>>   purely based on longest match:
>> 
>>   Candidate Source Addresses: 2001:db8:1::1 or fd11:1111:1111:1::1
>>   Destination Address List: ff00:1
>>   Result: 2001:db8:1::1 (prefer matching label)
>> 
>> 
>> IMO, this implicit specification causes several problems.
>> 
>> First of all, if you leave it to implementation, this creates an interoperability
>> problem. In the sense that a site administrator, an application developer, a
>> network designer, have to take care of the nodes with different address
>> selection behavior.
> 
> Are you arguing it should be mandatory, not optional?  (I'm guessing so based
> on the previous discussion of "macros" in the table.)
> 
> But still, you have to take care of nodes with different address selection behavior
> anyway if you allow heterogeneous hosts, since you'll have
> a) hosts that don't do RFC 3484
> b) hosts that do RFC 3484
> c) hosts that do 3484bis
> 
> And even within a category above, the IPv4 source address selection behavior
> will vary since that's not specified.
> 
> At best you can argue to minimize the problem as much as possible, but
> you can't make it go away.

Rather, my question was about the design choice.

Regarding the design of ULA and how to use the ULA, can we agree that 
ULA-to-ULA communication within the same /48 prefix is not always preferred
over other communications using IPv4 or IPv6 global addresses ?

>> Second,
>> when a user configures his policy table, the configured table is overwritten by
>> this implementation dependent policy injection behavior ?
>> Can the user suppress this behavior of policy injection ?
>> This issue should arise also when a policy distributing mechanism is ready.
> 
> Good questions.  Do you have suggested answers to those questions?
> I might throw out a strawman of:
> 
> Any automatic rows added by the implementation as a result of address
> acquisition MUST NOT override a row for the same prefix configured
> via other means.   That is, rows can be added but never updated
> automatically.   An implementation SHOULD provide a means for
> an administrator to disable automatic row additions.


My suggested answer for this was to use macros, which can be
added/deleted by a user, and interpreted as the actual prefix
attached to the hosts.

Best regards,

--
Arifumi Matsumoto
  NGN System Architecture Project
  NTT Service Integration Laboratories
  E-mail: arifumi@nttv6.net
  TEL +81-422-59-3334 FAX +81-422-59-6364