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List:       ipng
Subject:    Re: RFC6085 update to rfc2464bis
From:       Bob Hinden <bob.hinden () gmail ! com>
Date:       2017-01-13 0:36:51
Message-ID: 7EF1DB66-565A-4107-A5C2-EB4387CC9707 () gmail ! com
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Ole,

> On Jan 11, 2017, at 1:48 AM, otroan@employees.org wrote:
> 
> Bob, Jinmei,
> 
> As one of the authors of RFC6085 let me try to clarify how it would typically be \
>                 used.
> Scenario: Wireless AP that already knows the L2 unicast address of all stations on \
> a link. Some APs try to improve on IPv6 multicast on wireless by sending the RAs as \
> L2 unicast to each individual station. The AP then runs through it's list of L2 \
> unicast addresses and sends the multicast RA with the given L2 unicast mapping. 
> 2464bis says:
> An IPv6 multicast packet may also be mapped to a unicast Ethernet
> Link layer address as defined in Section 6.
> 
> An IPv6 node receiving an IPv6 packet with a multicast destination
> address and an Ethernet link-layer unicast address must not drop the
> packet as a result using of this form of address mapping.
> 
> 
> As Jinmei also says, referring to section 6 is then wrong. That implies that the \
> 6085 address mapping uses address resolution. Which is not the case. 
> 6085 is indeed very underspecified in stating how the mapping is done, from 6085:
> The determination of the unicast Ethernet link-layer
> address and the construction of the outgoing IPv6 packet are out of
> scope for this document.
> 
> 
> Either do (Jinmei): 
> An IPv6 multicast packet may also be mapped to a unicast Ethernet
> Link layer address as described in RFC6085.
> 
> Or something like:
> An IPv6 packet with a multicast destination address may also be mapped to an 
> Ethernet link-layer unicast address [RFC6085].
> E.g. when it is clear that only one address is relevant on the link and that the
> mapping between an IPv6 multicast destination address and an Ethernet link-layer
> unicast address is already known.

I agree with Jinmei and your comments that referring to Section 6 is not correct.  \
Adding the reference to RFC6085 is good, but as you note above, it doesn't describe \
how to do this mapping.  The text you suggest may be the best we can do.  It's not \
exactly an algorithmic mapping, as the node doing it needs to know something about \
the environment it is running in.  I guess this is the down side of using "Ethernet" \
on a variety of media that isn't a real multicast domain.  

Any other suggestions?

Bob


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