Re: [16NG] Re: Review of the ipv6-over-ipv6cs draft

["JinHyeock Choi" <[e-mail]>]

Dear Pekka

Thanks for your helpful review. Kindly find my in-line comments.

> > DNA for example. For DNA, a host relies on prefixes which were received
> > within 3 * Maximum of MaxRtrAdvInterval.
>
> Such behaviour would be incorrect, as RFC2461 says:
>
>       AdvDefaultLifetime
>                      The value to be placed in the Router Lifetime field
>                      of Router Advertisements sent from the interface,
>                      in seconds.  MUST be either zero or between
>                      MaxRtrAdvInterval and 9000 seconds.  A value of
>                      zero indicates that the router is not to be used as
>                      a default router.
>
>                      Default: 3 * MaxRtrAdvInterval
>
> So it is legitimate to have:
>
>  3*MaxRtrAdvInterval < AdvDefaultLifetime < 9000
>
> If what you say is true, DNA specification is incorrect.

I'm not sure why that's incorrect.

First take notice that it is NOT MaxRtrAdvInterval BUT Maximum of
MaxRtrAdvInterval. (This distinction is sometimes confusing, at least
to me.) According to RFC 2461, Maximum of MaxRtrAdvInterval is 30 min
but MaxRtrAdvInterval may differ from router to router.

        MaxRtrAdvInterval
                     The maximum time allowed between sending
                     unsolicited multicast Router Advertisements from
                     the interface, in seconds.  MUST be no less than 4
                     seconds and no greater than 1800 seconds.

Second a host simply stops using for DNA operation a prefix which was
not received within 3 * Maximum of MaxRtrAdvInterval but can keep
using the prefix as of RFC 2461.

This 3 * Maximum of MaxRtrAdvInterval rule is to remove the stale
prefix information quickly  because prefix lifetime can be quite long,
days or even weeks, for DNA operation.

> >> Even if a default route would be lost while in suspend, I don't see
> >> this as an issue as immediately when the host gets woken up, the
> >> default route could be re-obtained by a) specific RA (if wake up call
> >> was sent by the AR -- at the same time or 20ms later) or b) a RS (if
> >> host decided to wake up).  Later you also said that when a host gets
> >> paged it needs to establish the link, implying that in fact there is
> >> some delay before link can be used after paging.
> >
> > Well... If the AR is configured to send periodic RAs at regular
> > intervals (MaxRtrAdvInterval), the AR would end up paging the host and
> > waking it up to deliver an RA which is essentially not very useful
> > to the host.
>
> If this approach were to be chosen, MaxRtrAdvInterval would be set to
> something like 1800 seconds, but for example BS could filter out 80%
> of messages, so an RA would only be sent to MS every 8000 seconds.
> From the perspective of MS, filtering out RAs is indistinguishable
> from it packets getting lost in the network, so this would require no
> host modifications.

As you wrote above, assume MaxRtrAdvInterval is set to 1800 secs
(which happens to be also the Maximum of MaxRtrAdvInterval) and BS
filters out to deliver RA every 8000 secs.

Then after 5400 secs, from the lack of RAs within 3 * Maximum of
MaxRtrAdvInterval, hosts can deduce that it has missed at least 3 RAs
and stop using advertised prefix for DNA operation.

If MaxRtrAdvInterval is very close to Maximum of Max RtrAdvInterval,
filtering out some RAs may give hosts the wrong impression that there
is something wrong on the router/link.

Thanks for your kind consideration.

Best Regards

JinHyeock

_______________________________________________
16NG mailing list
[e-mail]
https://www1.ietf.org/mailman/listinfo/16ng