Re: [DNA] [Announce] DNA solution framework I-D

[Greg Daley <greg.daley@eng.monash.edu.au>]

Hi Jim,

Bound, Jim wrote:
> Hi Greg,
> 
> Once I know I have changed links at L2 and prefixes I had received I can
> be pretty sure the RA is from a new link and if it is completely
> different prefix. This would work for initial deployment too IMO.  My
> fear is for years IETF has tried to define such IDs and have not been
> successful or have been deployed well in the market when experimental.  

I think that the complete prefix list (CPL) idea is good to have
in a draft now.  It makes sense to use that information when
it can be built.

When arriving on a new link after the first RA reception,
we still need a means to distinguish between the
next RA from a different router on the same link, and
rapid transition (ping-pong) between different subnets.

The cpl draft has a couple of different ways to do this,
but really provides best performance when the interval
between link changes is > 12 seconds.

I'd like to see something which doesn't explicitly require
link-layer hints to do this.

If we need to revisit some of the other ideas and see
the rusted carcases of what not to do, then your or
others' experience will be very valuable.

> Other options are an ICMP message type to verify a new link or a new
> router RA link advertisement for MNs only.

I think that the big thing which was discovered when Bernard
looked into DNAv4 is that MIPv4 advertisements don't work
because they're not available everywhere.

We'd have to balance the cost of an facility not being present
(and relying on it, for example, if we had to send a different
message than an RS or an RA), as opposed to providing
enhancements to router and neighbour discovery, which are
almost universal.

The absence of our optimization then needs to have good
fallback cases.

using incomplete prefix lists may be good enough, if we take
into account the chance that there will be disjoint advertised
prefixes on a particular link (low?), and do binding signalling
even if we're only 95% likely to have received RAs from all routers.

If the incomplete information is not seen to be good enough,
LinkID's may be.  They're included in otherwise vanilla RAs as
options and have good failure cases if we move from a link containing 
them to one without (or the other way around), and complement the 
presence of prefix advertisements (but don't need them).

If they're not needed though, they're not needed.

> But if I were to look at IDs I would try to think about how AAA could be
> used per link.
> 
> We should have the discussion for sure but with the caveat if we are
> sitting here in 3 months and no good ID consensus is happening then use
> that as hint it may be stalling us for forward progress.

That's a very good idea.

Hopefully it won't take much effort to look into the
ideas, but if we're still blocked in 3 months (or less), I
think we'd be fairly unwise to not take your advice.

Greg