Date: Wed, 17 Mar 2004 03:32:06 -0800 From: Luigi Rizzo <luigi@iet.unipi.it> To: Karim Fodil-Lemelin <kfl@xiphos.ca> Cc: freebsd-net@freebsd.org Subject: Re: Dummynet Limitations Message-ID: <20040317033206.A23760@xorpc.icir.org> In-Reply-To: <40575A8F.8090402@xiphos.ca>; from kfl@xiphos.ca on Tue, Mar 16, 2004 at 02:50:39PM -0500 References: <40575A8F.8090402@xiphos.ca>
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On Tue, Mar 16, 2004 at 02:50:39PM -0500, Karim Fodil-Lemelin wrote: > Hi > > This code: > > <code> > if (pipe.delay > 10000) > errx(EX_DATAERR, "delay %d must be < 10000", > pipe.delay); > </code> > > in /usr/src/sbin/ipfw/ipfw.c > > Limits the pipe delay for dummynet to 10 seconds. Is there any reason > for this? Also, no such limit is imposed on the bandwidth why? > Memory (amount of mbufs/mbclusters) is obviously a limit here but I was > wondering if something else was hidden in this statement. back in 1996 when i wrote that line of code, my test machine had 16MB of RAM and i did not want to exhaust it with a poorly configured pipe. You are certainly welcome to increase it or even better make it into a sysctl variable. But keep in mind that pipe.delay is the propagation delay, and i cannot make any sense (except for simulating deep-space communications) of a larger delay, in which case, though, communication is so peculiar that almost surely you need a different test environment, not something IP-based as dummynet. Also, in such cases, you probably want to simulate things faster than realtime -- makes no sense to send a packet and wait hours for it to be delivered. cheers luigi
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