RE: [DNA] Model: how to treat "link down" events

[Mohan.Parthasarathy@nokia.com]

>> Erik,
>> 
>> Is the following scenario possible ?
>> 
>> 1) Host receives a link down event. Does not do anything.
>> 2) Host attaches to the new link. Link UP event happens
>>    slightly late or the event has not propagated completely
>>    through the system. Meanwhile you are able to send and
>>    receive packets. This is not good because you are not
>>    in the optimistic state yet and you are on the new link.
>
>We can't come up with any reliable DNA procedure in such a 
>case. One would more or less end up ignoring the 'link up' 
>event and just rely on the content of the RAs as suggested in 
>5 in CPL; but as stated that approach isn't robust; if a host 
>moves too often it can conclude that the union of prefixes 
>from multiple links are in fact the prefixes assigned to a single link.
>
>And the two authors of CPL and Thomas agree that we can drop 
>that section.
>
>So for a reliably DNA we do have to assume that the link up 
>event notifications are delivered in order relative to packets 
>arriving from the network interface.
>
The above case may not be an abnormal case. The "Link UP" event
needs to be processed even though it has been generated by
the lower layer. This may take some time. It is not atomic in
the sense that when the event happens,  no packets are allowed
till the event is processed. Do you think that this case is
a pathological case ?

>Note that draft-pentland-dna-protocol* can do slightly (as in 
>epsilon) better than CPL, since the DNA procedure can tie the 
>received RA to the RS one way or another. But this doesn't 
>help tell whether the prefixes received in periodic, 
>unsolicited RAs belong to one link or another when there is no 
>'link up' event notification.
>
But see my other mail. My concern is what happens before the
RS is sent and you are not receiving any RAs but some
neighbor solicitations on the new link.

-mohan

>    Erik
>