Re: [Softwires] MAP & 4rd-U - Preserving freedom of subnet-prefixes (V octet)

Ole Trøan <otroan@employees.org> Mon, 06 February 2012 08:33 UTC

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Cc: Softwires WG <softwires@ietf.org>, Yong Cui <cuiyong@tsinghua.edu.cn>, Ralph Droms <rdroms@cisco.com>
Subject: Re: [Softwires] MAP & 4rd-U - Preserving freedom of subnet-prefixes (V octet)
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Remi,

>>>> what happens with 4rd-U if the End-user IPv6 prefix is e.g a /96?
>>>> and the V-bits are not adhered to?
>>> 
>>> If the End-user doesn't support 4rd-U, nothing to be said. 
>>> If 4rd-U is enabled, any prefix longer than /64 that matches a Mapping rule MUST have the V octet.
>>> 
>>> If any you have a case where this isn't sufficient, I will look at it.
>> 
>> MAP is more flexible with regards to not depending on the V octet.
> 
> (a) Which flexibility? To do what? 

supports arbitrary end-user IPv6 prefix length, without regard for 'magic bits' in the interface-id.

> (b) Do you negate that:
> - with MAP as is, an IPv6 site may have to change its assignment of subnet prefixes to support MAP

only if the first subnet in the end-user IPv6 prefix is used by another internal router, that isn't going to act as a MAP CE.

> - This is never needed with 4rd-U, thanks to the V octet.

renumbering is in any case going to happen in the home, and we have to design our protocols to deal with it.

can we just agree to disagree on the V-octet, and not spend any more working group time on it? it would be good if you wrote up a more detailed analysis in a separate draft, so the considerations are kept somewhere.

cheers,
Ole