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catalyst 3750 and UDP traffic policing ?

 
 
RJ45
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      05-08-2004
Hello,
I noticed that traffic policing with C3750 (EMI) works only with
TCP Streams and not UDP streams.
anyone got the same result ?

thanks

Rick

 
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Walter Roberson
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      05-08-2004
In article <(E-Mail Removed)>,
RJ45 <(E-Mail Removed)> wrote:
:I noticed that traffic policing with C3750 (EMI) works only with
:TCP Streams and not UDP streams.
:anyone got the same result ?

If I remember correctly, traffic policing works in part by dropping
packets and expecting the other end to "notice" and start transport-level
decongestion procedures. TCP has decongestion procedures based upon
timeouts and window-sizes. UDP has no decongestion procedures: for
UDP you can't inherently tell the difference between the packet never having
been sent or it having been lost or it having been dropped for rate
control reasons. So UDP doesn't inherently know enough to slow down.

--
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Andrey Tarasov
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      05-08-2004
Hello, Walter!
You wrote on 8 May 2004 18:23:18 GMT:

WR> :I noticed that traffic policing with C3750 (EMI) works only
WR> with :TCP Streams and not UDP streams.
WR> :anyone got the same result ?

WR> If I remember correctly, traffic policing works in part by
WR> dropping packets and expecting the other end to "notice" and
WR> start transport-level decongestion procedures.

That would be Random Early Discard, or Random Early Detection which is
politically correct form of the former one

With best regards,
Andrey.

 
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Andrey Tarasov
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      05-08-2004
Hello, RJ45!
You wrote on Sat, 8 May 2004 18:00:16 +0000 (UTC):

R> Hello,
R> I noticed that traffic policing with C3750 (EMI) works only
R> with
R> TCP Streams and not UDP streams.
R> anyone got the same result ?

Normally TCP traffic is overpoliced so you might get very different results for
TCP and UDP even with policer working properly. How did you do the test and what
was the results?

With best regards,
Andrey.

 
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RJ45
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      05-11-2004

I did the test with iperf.
with TCP streams I got good results, with UDP
streams traffic is not shaped, is not policed.
if I configure a policy rule of 10Mbit/s
with TCP streams it works, with UDP streams it goes 100MBit/s
without policing it at 10Mbit/s.

my tests are 2 100Mbit/s machines connected to 2 different Layer 3 IP
ports of the switch.

Maybe traffic policy cannot work with UDP streams as Walter explained?

thanks

Rick

On 2004-05-08, Andrey Tarasov <(E-Mail Removed)> wrote:
> Hello, RJ45!
> You wrote on Sat, 8 May 2004 18:00:16 +0000 (UTC):
>
> R> Hello,
> R> I noticed that traffic policing with C3750 (EMI) works only
> R> with
> R> TCP Streams and not UDP streams.
> R> anyone got the same result ?
>
> Normally TCP traffic is overpoliced so you might get very different results for
> TCP and UDP even with policer working properly. How did you do the test and what
> was the results?
>
> With best regards,
> Andrey.
>

 
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Andrey Tarasov
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      05-13-2004
Hello, RJ45!
You wrote on Tue, 11 May 2004 13:14:02 +0000 (UTC):


R> I did the test with iperf.
R> with TCP streams I got good results, with UDP streams traffic
R> is not shaped, is not policed.
R> if I configure a policy rule of 10Mbit/s with TCP streams it
R> works, with UDP streams it goes 100MBit/s without policing it
R> at 10Mbit/s.

R> my tests are 2 100Mbit/s machines connected to 2 different
R> Layer 3 IP ports of the switch.

Can you post a config?

R> Maybe traffic policy cannot work with UDP streams as Walter
R> explained?

What Walter mentioned is called RED - random early detect. That doesn't work
with UDP streams indeed, because those streams are not sensitive to packet drops
and don't throttle.
Policer does the same thing to all traffic - either UDP or TCP - it drops (or
mark) the packets violating configured transmit rate.

With best regards,
Andrey.

 
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