From: Daniel Ginsburg (dginsburg@mail.ru)
Date: Fri Jul 30 2004 - 11:11:44 GMT-3
As far as I know timeout parameter affects only how long router waits
for reply before printing '.' instead of '!'.
I ran ping with default timeout, with 0 timeout and with timeout 100.
All three completed in approximately same time. My conclusion is that
rate of packets dictated only by round-trip time.
Please note that 50% is upper bound. It can be significantly less is
case of LFN (long fat pipe).
On Fri, Jul 30, 2004 at 03:56:58PM +0200, Richard Gallagher wrote:
> What about setting the timeout to zero? Then we don't ever hang around
> and wait for a response. We just send as fast as the router can.
>
> On Fri, 2004-07-30 at 15:29, Daniel Ginsburg wrote:
> > On Thu, Jul 29, 2004 at 10:50:38AM -0400, ccie2be wrote:
> > > Hey Richard,
> > >
> > > I don't dispute or disagree with what you're saying but how do know that 4
> > > simultaneous pings with a packet size of 1500 will load the channel to over
> > > 80%? How do you know what load exactly that will put on the channel? If
> > > you don't know exactly what load that puts on the channel, how do you know
> > > that that is NOT, for example, a 65% load or 75 % load?
> > >
> >
> > Unlike many other ping implementations which send 1 echo request per
> > interval cisco's one sends next echo request as soon it receives echo
> > reply or waits for timeout if request or reply is lost. So average
> > bandwidth utilization in one direction with one 'ping a.b.c.d size X'
> > will never exceed 50%.
> >
> > Let me illustrate this with the diagram
> >
> > ---
> > ^ BW
> > |
> > | (1) (3) (5)
> > |----- ----- -----
> > |
> > | (2) (4)
> > ----------------------------------------->
> > Time
> >
> > (1) router transmits ping request
> > (2) router waits for ping reply
> > (3) router transmits next ping request
> > (4) router waits for next ping reply
> > etc.
> >
> > So router uses the link almost[1] exactly half of the time. Please note
> > that this 50% figure almost[1] doesn't depend on size of echo
> > request/reply.
> >
> > [1] I'm saying almost because router needs to ponder a very short period
> > of time before replying to echo request. This period of time may be
> > negligible or not depending on speed of the link.
> >
> > Two simultaneous pings will theoreticaly saturate the link. Run four to
> > make sure ;)
>
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-- dg
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