On Nov 10, 2009, at 1:32 AM, [email protected] wrote:
In einer eMail vom 10.11.2009 08:04:50 Westeuropäische Normalzeit
schreibt [email protected]:
the presentation slides are at:
http://www.nanog.org/meetings/nanog44/presentations/Wednesday/Zhang_Wed_N44.pdf
Quote from these slides:
The problem: routing too flat
solution: add more hierarchies in addressing & routing
Yes, but do hierarchies right. There have been multiple hierarchical
proposals which did the hierarchical aggregation in the wrong way.
What it takes is a "sliding hierarchy" as provided by TARA so that
each router is fairly in the middle of the hierarchy and never at
the very rim.
Analogy: Imagine a city map for Istanbul, Turkey, with a Western
part containing each single street and an Eastern part being a
highly aggregated road map for entire Asia.
Or take Compact Routing studies which mentioned stretch factor
17 !!! Hierarchy is by no means a reason to enforce a path which is
longer than the shortest one! Neither when being in the middle or at
the rim ("Istanbul").
How many hierarchical levels is the right number? Who says "the less
the better" is wrong.
I have my doubts that the routing folks have a proper understanding
wrt hierarchies.
Heiner
Hi Heiner, a couple comments here.
1/ one needs to read this with the understanding of its context--the
quote you picked reflected understanding 15 years back.
the world has changes in significant ways since then
We understand much better now too.
2/ most importantly, I was calling attention to Postel's comments on
slides 7 & 8: these quotes were taken from the meeting minutes then:
- “Transport layer ID is not an issue that we
need be concerned with for now. Once we
decide what to do for IP addresses, then
transport people can easily figure out how
they may use the address.”
- “We must avoid circular dependencies;
- “we must define a substrate of the
system that can operate without DNS. ...
- “we must not depend on DNS to
bootstrap the core operation of the
system”
Personally I believe these design guidelines still hold true today.
Lixia
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