Date: Sat, 14 Dec 2002 18:07:33 -0800 (PST) From: Bsd Neophyte <bsdneophyte@yahoo.com> To: Greg 'groggy' Lehey <grog@FreeBSD.org> Cc: FreeBSD Questions <questions@FreeBSD.org> Subject: Re: Hubs and switches (was: uninformed qstn...) Message-ID: <20021215020733.46093.qmail@web20106.mail.yahoo.com> In-Reply-To: <20021215012545.GB144@wantadilla.lemis.com>
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--- Greg 'groggy' Lehey <grog@FreeBSD.org> wrote: > I'm not sure you meant to write what you did, but I'm not 100% I > understand. But yes, latency isn't an issue. Even if it is, switches > still win. My point is that generic switches are not faster than hubs, because of the added latency associated with the store-and-forward method. Cisco 2900's have the ability to do both types of switching. > I tried a test here between two machines on my network. In each case, > the data went via the Cisco 2900 switch and then either via a hub or a > second switch. The remote machine has a 10 Mb/s interface. Here are > the results (average ping time): > > Switch, normal ping: 0.756 ms > Hub, normal ping: 0.744 ms > > Switch, 1500 bytes: 4.251 ms > Hub, 1500 bytes: 4.004 ms > > Switch, 1500 bytes, load: 4.244 ms > Hub, 1500 bytes, load: 4.513 ms > > The "load" was a single concurrent tar over the network. I must say > I'm impressed how little degradation there was, but it's clear that > the latency savings on a hub are more than offset by its performance > under load. I would offer the rebuttal that when you look at costs, having a hub deal with 12-16 nodes would more than suffice. For example, a new catalyst 2912, depending on options, will run you between $2000-$5200, while a 12 port fast ethernet hub will run you about $200-$300. BTW, I don't know if your switch is configured for cut-through switching or store-and-forward. If it is set for store-and-forward, I'd suggest you change it to cut-through. I'm sure you can pick these up refurb'ed cheaper on ebay, but I wouldn't recommend buying anything that doesn't qualify for a smartnet agreement. I suppose if there isn't a big price difference between a generic switch and a hub, the switch would seem to be a better bet. You can add other switches or hubs to each port and keep the collision domain confined, unlike a hub which will add to it. > As I say, there were three machines involved in this test. The > collision light was on almost continually: Both my cisco istructors are probably frowning on me if they knew I wasn't cursing hubs, but with all those collisions, did you take a huge performance hit that would warant spending at least an additional $1800. On a separate note. I love your book. __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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