Re: [Roll] Something to ADD

[Richard Kelsey <richard.kelsey at ember.com>]

   From: JP Vasseur <jvasseur at cisco.com>
   Date: Tue, 10 Nov 2009 12:43:37 +0100

   We need to clarify that when a node jumps to a better parent (higher  
   rank), it can of course jump at any time since there is no risk of  
   loops, but it must also poison up (send a no-DIO) to the previous  
   parent.

JP,

Unfortunately, it isn't that simple.  The problem is that
some nodes may be caching DIO data while others are not.
If a node jumps to a new parent, whether up or down, the
issue is whether or not this causes the moving node's DIO
to be cached by a different ancestor.

 - If the DIO is still cached by the same ancestor,
   then the moving node just has to send a new DIO
   to its new parent and all will be well.

 - If the DIO is now cached by a different ancestor,
   then the moving node needs to send a no-DIO before
   moving and it and all its descendants must send
   new DIOs after the move.

Not only is the second case potentially quite costly, but
there is currently no way for a node to know which case
applies to a given move.

                         -Richard Kelsey