QoS for CEM traffic

Unanswered Question
Jul 7th, 2008

I have two 3750ME switches connecting two ends of a LES100. On each switch, i have 3845 routers with the NM-CEM-4SER modules, plus direct to switch internet traffic. My complete setup is as shown in the attached PDF.

My problem is that with the default QoS settings, i have lots of drops in the Txqueue of the switches.

The CEM's send traffic as EF, which is trusted throughout the switch setup. Other traffic that comes into the switch is marked down to best effort. Thus, most of the traffic the switches handle is EF,(about 70%, 20MB for now). How do i tune the QoS parameters on the switch to handle this amount and more of EF traffic?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
jsivulka Fri, 07/11/2008 - 06:45

Regaring the QOS, I think we should implement this on the 3750 . It is worth advising you to first upgrade the IOS on this device. The following URL will help you:


As you are unable to specify the "bandwidth/priority" on 3750 cli, you will need to use the Queuing and Scheduling (SRR) section from the config guide. So basically you enable the expidite queue for the CEM traffic egreesing the 3750. However I believe you cannot classify the traffic via acl to assign it to queues, so you will need to mark it.

pkanyion Sat, 07/12/2008 - 09:37

I would suggest that you apply CBWFQ + LLQ as scheduling strategy, enabling you to contineously forward EF traffic, ignoring any best effort traffic, as long as EF traffic is available. Also apply WRED to take care of congestion.


This Discussion