Re: [RRG] Routers in DFZ

[Peter Sherbin <pesherb@yahoo.com>]

Here is a good comment on the recent RRG discussion about routers in DFZ and
relationship between number of prefixes and the processing power. Details are below
and here is the essence:

> 	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.

In particular it provides a theoretical limit that can be added to the Problem
Statement draft-narten-radir-problem-statement-00.txt

Thanks,

Peter


--- bmanning@vacation.karoshi.com wrote:

>  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	
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