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Date: Thu, 01 Dec 2011 10:25:28 -0800 From: Rick Jones <rick.jones2@...com> To: Stephen Hemminger <shemminger@...tta.com> CC: David Laight <David.Laight@...LAB.COM>, Hagen Paul Pfeifer <hagen@...u.net>, Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org Subject: Re: [PATCH v3 net-next 2/2] netem: add cell concept to simulate special MAC behavior On 12/01/2011 08:57 AM, Stephen Hemminger wrote: > On Thu, 1 Dec 2011 16:38:51 -0000 > "David Laight"<David.Laight@...LAB.COM> wrote: > >> >>> One idea to do small delays at higher speed is to insert >>> dummy pad frames into the device. >>> It would mean generating garbage, but would allow for >>> highly accurate fine grain delay. >> >> Not a good idea. >> They would have to be sent to a known MAC address >> otherwise all the ethernet switches would forward them >> on all output ports. >> >> David >> >> > > Yes it would have to be a constant destination, not sure if there > is a discard value in Ethernet protocol spec. Aren't there special addresses that aren't supposed to be forwarded by (intelligent) switches? IIRC LLDP uses such things. Though the IEEE may take a dim view of using it for such a purpose, and knuth only knows what switch bugs would be uncovered that way... http://standards.ieee.org/develop/regauth/grpmac/public.html http://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol rick jones -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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