[c-nsp] Traffic shaping Cisco 3550 (fwd)

[Tim Devries]

According to 

http://www.cisco.com/en/US/products/hw/switches/ps646/products_tech_note0918
6a00800feff5.shtml


To sustain the specified traffic rate, the burst should be no less than the
sum of the following equation:

Burstmin (bits) = Rate (bps) / 8000 (1/sec)  

For example, calculate the minimum burst value for sustaining a rate of 1
Mbps. The rate is defined as 1000 Kbps, so the minimum burst needed is the
sum of the following equation:

1000 (Kbps) / 8000 (1/sec) =125 (bits)  

Also here is a good link with regards to QoS Caveats

http://www.cisco.com/en/US/products/hw/switches/ps646/products_configuration
_guide_chapter09186a008007d733.html

You can shape in and out, using different policy maps (with limitations on
shaping outbound using acls).  One approach is to shape on the ingress port,
and then apply another policy map inbound on your uplink(s).

I struggled with QoS on the 3550 for a while, due to the fact that my
monitoring software (real-time 1/sec snmp) was showing the port I was
monitoring as spiking well above the threshold I had set.  Be aware that you
will not be able to see whether your policy is having any effect if you are
trying to look at the traffic statistics of the port.  This is because the
interface stats will always show the result before policing.  One way to do
it is to look at your upstream port, but you will have to try and separate
the individual customer from the aggregate which is nigh on impossible
(other than adding up all of your QoS values for all ports and ensuring that
the aggregate value conforms).

On the upside, I can at least see if a customer is consistently sending more
traffic than their shaped rate, and if so pass that information to sales, as
they would likely want to upgrade.

Thanks,

Tim


-----Original Message-----
From: Roger Wiklund [mailto:copse at xy.org] 
Sent: Thursday, January 27, 2005 10:36 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Traffic shaping Cisco 3550 (fwd)



Hi,

I´m trying to shape a port to 30mbps on a Cisco 3550.

Im using a policy map on ingress, but can I use it on egress also?

What is the correct way to shape in/out? And also, what is the optimal 
burst rate for 30mbps? I want to have as little TCP sawtooth effect as 
possible.

Thanks

/Roger

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