Re: 6MAN WG Adoption Call: draft-nordmark-6man-rs-refresh-01

[Lorenzo Colitti <[e-mail]>]

On Sat, Apr 18, 2015 at 2:34 AM, Erik Nordmark <[e-mail]> wrote:

> The reason is as follows: as noted in section 8.2, in the presence of
>> hosts that do not support this specification, routers must send periodic
>> Router Advertisements, otherwise the "timely and scalable reconfiguration
>> capabilities" cannot be maintained. This mode provides no power savings
>> over the status quo.
>>
> Lorenzo,
>
> I think you must be making some unstated assumptions in coming to that
> conclusion, because it does not match my conclusion.
>
> This specification allows a host to go to sleep and turn of its radio,
> which includes not being awoken by any multicast RA, and when it wakes up
> it can send a RS to refresh the information that might have changed while
> it was asleep. That provides power savings for that host.
>

But then the "timely and scalable reconfiguration capabilities" cannot be
maintained. The network can't tell that host about any new information,
because that host won't receive it. The host will only receive it when it
wakes up next.


> The document says that the network can operate in a mode where multicast
>> RAs are suppressed if it is known that all hosts on the link support the
>> specification. However:
>>
>>  1. It is impossible to know with certainty when a legacy node has
>>     joined the network. If a legacy host's three initial Router
>>     Solicitations are missed, then that host will never again send an
>>     RA, and will never get IPv6 connectivity unless it disconnects and
>>     reconnects. In contrast, today the node will get IPv6 connectivity
>>     as soon as it receives a periodic RA.
>>
>>
> As I pointed out in some earlier email, a host which is subject to packet
> loss so that the initial RAs are lost does not see any useful service. Your
> "as soon as" is currently as bad as 30 minutes (and separate discussions
> about MaxRtrAdvInterval might increase this to 6 hours). I don't know which
> host will wait for that long. Thus I don't think you can claim that legacy
> hosts work under such packet loss conditions.
>

It depends how frequent the RAs are. In general purpose networks, they
might be more frequent. Also, any node joining may cause a solicited
multicast RA. Depending on the application, "after 10 minutes" may be a lot
better than "never".

What about points #2 and #3?