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New Member

QoS problem in a 3550


We have a problem with a 3560 switch when we use the function 'mls qos trust dscp'.

When we enable this trust command on the interface we reduce the traffic flow to about 4,5 Mbit/s. Regardless if the interface id 10, 100 or gigabit.

If we remove the command we get full wire speed. If we use 'trust cos' we also get full wire speed.

If the command is there and we turn off 'mls qos' globally we get wire speed again.

It doesn't seam to matter of the links are trunks, tunnels or accessports nor if the equipment I connected directly or via a network.

/Regards Rikard

Cisco Employee

Re: QoS problem in a 3550

What is the IOS that you running on the switch. You might be hitting CSCsc96037.


Configuring Quality of Service on a CAT3560 or CAT3750 running any IOS can cause certain TCP

applications such as NFS to run slower.

Try upgrading it to the latest IOS and see if that helps.

-amit singh

New Member

Re: QoS problem in a 3550


No luck with the upgrade.

We have done some test with Chariot, and none of the test gets over 4 Mbit, so it seams to be more then NFS.

/Regards RIkard

Cisco Employee

Re: QoS problem in a 3550

Hi Rikard,

Are you using auto-qos on the switch or defining your policies manually. What happens if you remove the QOS config and enable the auto-qos only on the switch.

After doing some more research, I see a few more bug hits but anyone of those doesnot come close to the problem you have. Have you opened a TAC case for this behaviour? Please open a Service request with TAC and see if they can findout something on it.


-amit singh

New Member

Re: QoS problem in a 3550


We have configured QoS manually, and don't want to use auto-qos. (it we not work so well with the design)

A TAC case will be the next step.

Thanks Rikard

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