On Dec 21, 2008, at 12:53 PM, William Herrin wrote:
On Sun, Dec 21, 2008 at 10:29 AM, John G. Scudder <[email protected]>
wrote:
On Dec 21, 2008, at 10:26 AM, William Herrin wrote:
Not so. Cisco fast switching implemented a cache coupled with the
router's FIB. The FIB was constructed in part from the BGP RIB,
but it
was its own full database.
Seems like an unimportant difference in terms of system dynamics
but maybe
I'm missing your point.
Hi John,
The point is that the methodology is incorrect. They're not coupled.
Practically speaking, this is not correct, all the more so in an
architecture where there is a highly notional separation between the
different data structures in question.
The BGP RIB-level activity implies nothing about the fast switching
cache-level activity and vice versa. If you want to understand the
operational characteristics of caching, you'd be looking in the wrong
place.
We have real-world operational experience that says otherwise.
Looking at cache to RIB, best case you glean no useful information.
Worst case you find correlations that imply a false causation matrix,
contaminating any decisions you make with the information.
Think of it like a boxcar on a railroad. If you want to understand the
behavior of the boxcar, you don't look at its relationship to the
engine. You look at its relationship to the car in front, the car
behind and track below.
To extend the analogy, do you mean to assert that the engine has no
relevance to the behavior of the boxcar?
--John
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