QoS between two catalysts 3750

Unanswered Question
Nov 12th, 2009

we are running a transparent 2Mbit L2 link between two sites with a catalyst 3750 on each (connected to a fast ethernet port)

we want to implement qos to priorize 320Mbit for EF and 600 Mbit for AF3.

the EF packets are already marked; the packet for the AF3 have to be marked first.

Has anyone done already a similiar setup?

I have this problem too.
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Giuseppe Larosa Sat, 11/14/2009 - 02:12

Hello Frank,

if you are using bridging over a WAN link and no L3 device is involved you can try to take advantage of SRR queueing in C3750

>> In shaped mode, the egress queues are guaranteed a percentage of the bandwidth, and they are rate-limited to that amount. Shaped traffic does not use more than the allocated bandwidth even if the link is idle. Shaping provides a more even flow of traffic over time and reduces the peaks and valleys of bursty traffic. With shaping, the absolute value of each weight is used to compute the bandwidth available for the queues.



the shaped mode should be the one that fits your needs.

you need to configure appropriate marking on ingress interfaces


with routers you could use hierarchical QoS shaping all traffic to 2 Mbps and invoking a child policy with a scheduler.

with C3750 switches you may be able to find only an approximate solution

Hope to help


FRANK SCHADE Sun, 11/15/2009 - 07:32

Hi Giuseppe,

thanks for your answer. It confirms the results of my "studies" that the 3750 is not the most flexible platform for QoS.




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