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Re: [mif] WG Review: Multiple InterFaces (mif)

2009-04-22 16:53:41
Excerpts from Margaret Wasserman on Wed, Apr 22, 2009 10:29:07AM -0400:
Lars Eggert wrote:
On 2009-4-22, at 2:19, Christian Vogt wrote:
It seems that folks are considering two related, yet still orthogonal
topics for inclusion in the MIF charter:

- Conflicts between configuration parameters.

- Issues with address selection.

I agree that both of these are important and should be worked on (and  
with the rest of your email, basically).

The first one is what I thought MIF would be focusing on, as an INT WG  
is IMO the right venue for this.

The second one is also important, but much more tricky, because it  
ties in with transports and applications (as Keith and others have  
pointed out already). Topics that cross area boundaries are always a  
bit difficult to charter. I'm at this point not fully convinced that  
simply throwing this in with topic #1 into one WG is going to work.

I disagree with your conclusion for two reasons:

(1) As I pointed out in my previous message to Christian, address  
selection is not (today) a transport-layer or application-layer function  
in most cases.  Given that this is currently an Internet-layer function,  
I think it makes sense to analyze the issues with address selection (as  
part of the whole address/interface/router selection process)  in an  
Internet Area group.  If we find that one of the problems we have is  
that the Internet layer doesn't have the right information to make these  
decisions, then possibly some follow-on work might need to be chartered  
elsewhere.

(2) There is no way that these decisions can be made solely at the  
transport or application layer, because source (and to a lesser degree  
destination) address selection is tightly tied to the first-hop  
forwarding decision.  The outbound interface, source address and default  
router all have to be selected in a coordinate process, to avoid sending  
traffic that will be discarded on the outbound path, due to router 
filters.

So, while agree that address selection affects transport layers and  
applications, and that it might be necessary for transport layers and  
applications to have better ways of influencing it, I do not believe  
that address selection is a transport layer or applications layer  
function today, nor do I think it can be done solely at those layers in  
the future.

Margaret

The first problem (configuration conflicts) is best dealt with before
the second problem (address selection) even arises.  First I
initialize my interface, and then I use it.  They impinge on each
other but they are not tightly bound to each other -- they do not have
to be worked on in the same Working Group.  

I suggest chartering MIF to focus on problem #1, let it make progress,
and in the meantime figure out how to organize work on problem #2 in
parallel.

Scott
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