Some thoughts about "path failover"

 
Hi,

I was thinking about various multihoming scenarios in MOBIKE, 
and here are some ideas for starting a discussion...

First, it seems that there are two kinds of events that might
cause something to occur:

1) Either party notices a change in its own network interfaces
   For instance, L2 carrier is lost, default router stops 
   responding to ARP, new link appears, IP address changes, etc.

2) There seems to be a problem with the currently used path;
   e.g. lack of packets, or perhaps an ICMP message.

In case 1, it's quite clear who should handle the problem. This
case doesn't even require address lists: the party that notices
something can simply send an update message saying "my new
address is X".

Case 2 is more complicated, since it does not tell where the
problem is. Presumably both ends can detect the problem, and
will eventually do so. But which end should do something about
it? And if both ends are multihomed, which of the remaining
paths should be used?

These two cases seem to also require quite different messages 
from the protocol. Case 1 is just "my new address is X"
message: reasonably simple to implement, especially at the
receiving end.

Case 2 seems to require some kind of address lists, but this
might not be enough. For instance, it might make sense to
distinguish "primary path" (or "primary address") from "current
path" (that is used for traffic now), since we might want to
switch back to the primary path when it becomes available again.

One option which might simplify case 2 is that the parties
would agree in the beginning which of them (only one) is 
responsible for this "path failover" functionality... or
are there some failure cases I haven't considered?

Best regards,
Pasi