Re: [Softwires] Problem in draft-ietf-softwire-multicast-prefix-option

<mohamed.boucadair@orange.com> Wed, 08 June 2016 14:50 UTC

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From: <mohamed.boucadair@orange.com>
To: ian Farrer <ianfarrer@gmx.com>, "softwires@ietf.org" <softwires@ietf.org>, Jacni Qin <jacni@jacni.com>, "dxhbupt@gmail.com" <dxhbupt@gmail.com>
Thread-Topic: Problem in draft-ietf-softwire-multicast-prefix-option
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Date: Wed, 8 Jun 2016 14:50:51 +0000
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Subject: Re: [Softwires] Problem in draft-ietf-softwire-multicast-prefix-option
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Hi Ian,

Please see inline.

Cheers,
Med

De : ian Farrer [mailto:ianfarrer@gmx.com]
Envoyé : mercredi 8 juin 2016 16:11
À : softwires@ietf.org; BOUCADAIR Mohamed IMT/OLN; Jacni Qin; dxhbupt@gmail.com
Cc : dhcwg-chairs@ietf.org
Objet : Problem in draft-ietf-softwire-multicast-prefix-option

Hi,

On reviewing this draft I would like to raise a problem with section 5 of the draft. The text is:

"If all the enclosed IPv4-embedded IPv6 multicast prefixes have the same scope, the first instance of the option MUST be used."

The problem is that this contravenes section 17 of RFC7227:

Option order, either the order among many DHCPv6 options or the order

   of multiple instances of the same option, SHOULD NOT be significant.

   New documents MUST NOT assume any specific option processing order.



[Med] That sentence does not assume any (preference) order. It does only provide one way to select one instance among that list. As a reminder, the server is supposed to return one instance (per scope).


I raised this with the DHC WG chairs, and they have a couple of suggestions:

1. Define an encapsulating option - as the data inside an option can be order dependent.
2. Add a “preference” (octet?) and then a client can sort them based on this preference.

Thanks,
Ian