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RE: Comments on draft-yourtchenko-colitti-nd-reduce-multicast

"Hemant Singh (shemant)" <shemant@cisco.com> Fri, 21 February 2014 18:57 UTC

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From: "Hemant Singh (shemant)" <shemant@cisco.com>
To: Ole Troan <otroan@employees.org>
Subject: RE: Comments on draft-yourtchenko-colitti-nd-reduce-multicast
Thread-Topic: Comments on draft-yourtchenko-colitti-nd-reduce-multicast
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Date: Fri, 21 Feb 2014 18:56:55 +0000
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References: <5305AF13.5060201@acm.org> <75B6FA9F576969419E42BECB86CB1B89115F99A9@xmb-rcd-x06.cisco.com> <2730F679-46FC-416E-8DBB-D74676E637CA@employees.org>
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Cc: Erik Nordmark <nordmark@acm.org>, "Andrew Yourtchenko (ayourtch)" <ayourtch@cisco.com>, 6man WG <ipv6@ietf.org>
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Ole,

-----Original Message-----
From: Ole Troan [mailto:otroan@employees.org] 
Sent: Friday, February 21, 2014 12:32 PM
To: Hemant Singh (shemant)
Cc: Erik Nordmark; 6man WG; Lorenzo Colitti; Andrew Yourtchenko (ayourtch)
Subject: Re: Comments on draft-yourtchenko-colitti-nd-reduce-multicast

>RFC4861:
>   Note, however, that a Prefix Information option
>   with the on-link flag set to zero conveys no information concerning
>   on-link determination and MUST NOT be interpreted to mean that
>   addresses covered by the prefix are off-link.  

The RA has the A-bit set and the L-bit cleared.  So as per the specification text above the L-bit is zero and the host does not get any on/off--link determination from the L-bit for the addresses covered by the prefix in the PIO.   The host configures its ipv6 address from the PIO in the RA using SLAAC.  Now the host has to send a packet out an interface and the packet destination in the host's Neighbor Cache.  The packet destination also matches the host's prefix to a /64.  So what does the host do?  

Issue 

(a) an address resolution NS (assuming the destination is on-link) due to SLAAC operation.

or

(b) send the packet to the default router(s).  The L-bit has conveyed no on- or off-link information.  So doesn't the host resort to (a) above.  If the host choses to go to operation (b) what signaled to the host that the destination is off-link?   If the host picked (a), why is that?

If you can't determine one concrete choice from the two above, we have an ambiguity. 

Hemant

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