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 {elided} ------------------------------- & ------ Forwarded Message ------ Date: Tue, 07 Aug 2007 To: bmanning@karoshi.com 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. --bill