Re: [DNA-BOF] Do we need a separate DAD Problem Statement? (was Re:About Charter, DAD, and SEND)

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

Hi Bernard,

Bernard Aboba wrote:
>>I agree that here may be a problem.  However, I also think that we
>>will need to change the TCP algorithms somewhat due to intermittend
>>connectivity anyway.
> 
> 
> This is not an intermittent connectivity problem -- the link is up, it is
> just that the host might be using the wrong address.
> 
> One way to deal with this might be to clear the ARP/ND cache on a "linkup"
> event.  That way, the linklocal packets would not be sent unless the
> destination were onlink.  Packets destined to the default gateway would
> not be sent unless the host were on the same subnet. However, this is not
> "optimistic" in that it will only allow sending of traffic after
> reachability can be demonstrated -- phase 1 of DNA.  If reachability
> cannot be demonstrated, then there is little point in sending traffic --
> the host knows it is on the wrong subnet and needs to obtain a CoA.
> 

I think this is a really interesting issue (ND/ARP cache validity
on the link).  If we're to make best use of wireless link resources,
it may be useful to keep ND or transmission state as 'Latent',
rather than flush ND, until router information (in ND, indicated
by an isRouter flag) is confirmed through DNA.  This would prevent
ARP/ND storms or delays due to backoff timers, in the case where
IP information is unchanged.

Even if the ND cache or transmission state is latent, packets could
still be sent for DNA purposes of course, but we'd have to examine
whether other traffic would be paused, sent or discarded (for example,
if it takes a long time to do DNA, then VoIP packets are better
dropped).

This could prevent loss of entire windows in TCP, since the IP
send buffers would be tied to the transmission (or at least ND) state.

Greg