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Re: [RRG] Not moving the problem to the global mapping system



Robin Whittle wrote:
Hi Brian,

You wrote, in part:

I can't say how much I agree with this. If the mapping system
degenerates into a reachability-driven routing system, we might
just as well switch to two layers of BGP immediately.

I would suggest turning this into a concrete goal, such as:

<strawman>

The update rate in the mapping system should be at least
two orders of magnitude less than the update rate in
the BGP4 system, at any point in time.

</strawman>

This might be a reasonable goal or constraint if it was assumed that
the map-encap's mapping system was as costly and problematic (with
problems like convergence time, amplification of changes due to
routers flapping, making half-baked decisions based on limited
information, unfair burden of costs etc.) as BGP is today.
>
> [snip]
>
> Ivip is a map-encap scheme which violates what I think are the
implicit assumptions behind your strawman text: that mapping changes
in the mapping distribution system are at least as burdensome - due
to intrinsic costs and probably the unfair distribution of costs -
as updates are in BGP today.  So I don't think proposals such as
Ivip should be constrained as you suggest.

Hi Robin,

I think your complaint stems from the fact that Brian did not include any metric of (non-monetary) update cost in his strawman. We must have /some/ constraint on mapping updates -- no matter how little processing a single Ivip mapping update requires, its (non-monetary) cost is still non-zero. Ivip is unique among the proposals, as you mention, in the following way: all other proposals intend to guarantee either fewer pushed mapping updates compared to BGP, or pull-only updates /by design/. It /might/ be true that the update cost in Ivip is manageable due to human or economic factors, but that is only speculation at this point, and not enforced by the design.

So all I am saying, and I believe most people on this list would agree, is that we need some objective, scientific metric by which to judge whether a design is likely to solve the problems in question without causing new ones. Something where we can do a quantitative evaluation. If, as you suggest, Ivip does not cause problems due to large update volume, such an evaluation could prove you right!

-Michael

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