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

 
Pasi,

A few questions below..

> 
> 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]
>
I am assuming that this changes later on when the current path fails.
Right ?

>    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

Are you assuming that you always choose the first element (which is preferred) ?
If A wants to move the traffic to IPv6 interface, why can't it just send the
traffic to the IPv6 address in the B list ? I am confused as to why this
is not possible.

>   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.)
> 
Yes, if we want either end to control how the traffic flows, then
we need assymetric behavior. 

-mohan


> Best regards,
> Pasi
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