RE: Thoughts about issues 10/19: changing address vs. paths, and so on...

During the meeting today, Francis pointed out another possibly
option not really covered by 1-4.

Option 5: "Peers decide the source addresses independently"

   Host A                           Host B
   ------                           -------

   List_A = (decided by A) -->

                                <-- List_B = (decided by B)

   dst = List_B[1]                  dst = List_A[1]
   src = f_A(List_A, List_B,        src = f_B(List_B, List_A,
             local preferences,               local preferences,
             local info about                 local info about
             connectivity,                    connectivity,
             whatever)                        whatever)

Pros and cons:
+ Reasonably simple
- No guarantee A-to-B and B-to-A traffic choose the same traffic 
  pair (which complicates things with stateful packet filters)
- Host A can't move the "upstream" traffic to some other interface
  without co-operation from B (if we have partial connectivity). 
  For instance, if Host A has one IPv4 interface and one IPv6 interface, 
  A can't move the traffic to the IPv6 interface unless it somehow 
  convinces B to reorder List_B: how does this happen? (And if the
  answer is that List_B depends on List_A which depends on List B,
  how does this work?)
- The same thing also applies to failures in the middle: even
  if both parties' addresses and preferences stay the same,
  somehow they must reorder either List_A, List_B, or both.

(Hmm, I think that any option that is fully symmetric will have 
these problems.. but there are certainly options that are 
less asymmetric than option 3.)

Best regards,
Pasi