Re: [RRG] More discussion please: mapping churn

["William Herrin" <bill@herrin.us>]

On Sun, Mar 30, 2008 at 10:03 PM, Tony Li <tony.li@tony.li> wrote:
>  There hasn't been much discussion on the mapping churn rate.  There have
>  been a few good questions, but not much back and forth.  Do folks have an
>  opinion or should I just propose some text?

Hi Tony,

I think there may be four relevant numbers:

Maximum per-machine RIB-style update rate, that is map updates which
are conveyed by the machine but not used in the machine's forwarding
plane

Maximum per-machine FIB update rate for TCAM-based FIBs

Maximum per-machine FIB update rate for hardware-accelerated trie-based FIBs

Maximum per-machine FIB update rate for non-accelerated trie-based
FIBs (read: generic x86 server)


I have trouble imagining a system that doesn't have to contend with
some or all of these limits. No matter how cleverly we structure it,
our system will still be composed of individual machines.

Call me crazy, but I think we pretty much understand how RIBs and FIBs
work within the scope of an individual machine and we know what we can
expect with hardware available today. We can punch BGP routes into
Quagga unbound from server route table and see where it chokes to get
a decent estimate of the maximum per-machine RIB update rate. Similar
strategies should work for the other three. Whether the knowledge
source is a map or a route doesn't make much of a difference at the
individual-machine level. Or am I wrong?


I don't think there is a useful way to pre-assess system-wide maximums
aside from asking proposal authors to specify how tightly bound the
system-wide maximum is to the heaviest-loaded machine maximum and then
justify that analysis.

Regards,
Bill Herrin

-- 
William D. Herrin ................ herrin@dirtside.com bill@herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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