too many variables

bmanning at bmanning at
Thu Aug 9 16:21:37 UTC 2007

 I asked this question to a couple of folks:

	"at the current churn rate/ration, at what size doe the FIB need to 
         be before it will not converge?"

 and got these answers:

--------- jabber log ---------
a fine question, has been asked many times, and afaik noone has
provided any empirically grounded answer.

a few realities hinder our ability to answer this question.

(1) there are technology factors we can't predict, e.g.,
        moore's law effects on hardware development
(2) there are economics and policy and social factors we
        can't predict, e.g., how much convegence-capable
        hardware will providers/vendors be able to afford,
        how those costs will affect consumer prices,
        how that will affect consumer uptake, network
        growth, and industry dynamics, how regulation affects
        all of the above
(3) We Don't Have Any Data from providers on the dynamics of BGP
        and IGP interactions, much less network wide convergence,
        so the research community can't provide any empirically
        grounded input into an answer

------ Forwarded Message ------

Date: Tue, 07 Aug 2007 
To: bmanning at
Subject: CPU Usage

Router		      Upstream Uptime		BGP cpu per 1 sec uptime
Cat6500/SUP720		1	>1yr		53ms/sec
C7200/NPE-G1		1	158days		15ms/sec
C7304/NSE100		4+2	177days		55ms/sec
C7200/NPE-G1		1+2	26days		 8ms/sec
C7301			1	214days		 7ms/sec
GR2000			0+1	101days		 6ms/sec

Upstream: M+N, M is # of EBGP with full route feed , N is # of IBGP
with full route feed

Provided if the CPU consumption is propotional to the routing table
size, the hard limit would be 10 times to the current size, allowing
other tasks to obtain some CPU cycles.

----- End forwarded message -----

	so, one might presume that w/o a change in algorithm, and unlimited
	memory, that the CPU would run out of cycles to compute convergence
	at ~ 10x the current size of the routing table (abt 250,000 prefixes).

	so putting a stake in the ground, BGP will stop working @ around
	2,500,000 routes - can't converge...  regardless of IPv4 or IPv6.
	unless the CPU's change or the convergence algorithm changes.


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