[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <4ED7C698.40003@hp.com>
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
Powered by blists - more mailing lists