Re: [v6ops] new draft: draft-yc-v6ops-solicited-ra-unicast

[Mark Smith <[e-mail]>]

Hi Erik,

On 24 July 2015 at 02:26, Erik Nordmark <[e-mail]> wrote:
> On 7/23/15 2:37 AM, Mark Smith wrote:
>>

<snip>

>>> If not, then the implementation needs to multicast the RA.
>>>
>> I was wondering if instead the implementation could trigger an ND/NS
>> transaction for the RS source address at that point, and then unicast
>> the RA when that completes.
>
> That would only address the lack of SLLAO case; not the unspecified source
> address case.

True. I think the only option to unicast responses for unspecified
source address cases would be link-layer unicast option.

> I don't know how common these cases are in existing implementations.
> The unspecified source would appear if the host is doing DAD in parallel
> with sending the RS.

I did some capturing/research related to this draft, Windows XP was
issuing unspecified source RSes at boot, then using link-local sourced
RSes, although the later versions of Windows I looked at didn't.

> I don't know when a host would omit the SLLAO in the RS.
>

I think it would be fairly common at the moment. The Linux user
interface oriented Network Manager utility
(https://wiki.gnome.org/Projects/NetworkManager), used by at least
Fedora, is sending RSes without the SLLAO, as it uses the libndp.org
library, which only seems to currently support building a minimal
generic RS without the SLLAO option, and there doesn't seem to be an
obvious library call to add an SLLAO to the generic RS.

>>

<snip>

>
> I think there is text earlier to say to not create an NCE for 0::0 nor if
> there is no SLLAO (unless the link-layer has no addresses).
>

I've done some more searching of RFC4861, and haven't seemed to find
anything that specifically prohibits creating an NCE via a ND/NS
transaction for a RS without an SLLAO.

Thinking about it more, triggering an ND/NS to resolve the source
address of the RS if there is no SLLAO may not be all that beneficial,
as it effectively substitutes a multicast ND for a multicast RA. There
might be some other benefits from having router(s) having proactively
resolve a host's link-local RS source address that make trading a
multicast RA for a multicast ND worth while.

Regards,
Mark.

> Regards,
>    Erik
>
>>
>> Performing an NS/ND to resolve the source address of the RS without a
>> SLLO would seem consistent with the corresponding RS SLLO handling -
>> to load the Neighbor Cache with entries for nodes that have sent RSes.
>>
>>
>> Regards,
>> Mark.
>>
>>>     Erik
>>>
>>>> https://www.ietf.org/mail-archive/web/v6ops/current/msg22464.html
>>>>
>>>>
>>>>
>>>>
>>>> https://www.ietf.org/mail-archive/web/v6ops/current/msg22464.html
>>>>
>>>>> But I would not say it's sufficient, if only from an "explicit
>>>>> clarity" standpoint.  I think explicit mention of RAs and the other
>>>>> discussion is helpful for implementors not inclined to dig to great
>>>>> depths or just seeking explicit confirmation.
>>>>>
>>>>
>>>>
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>