Incorrect QoS Configuration Caused Network Traffic Outage

Issue

QoS implementation caused an outage when trying to restrict the bandwidth with QoS profile for a particular class.

Details

The example below shows an incorrectly configured profile which is attached to the QoS interface.

In this example scenario, a 10Gb interface is used and the screenshot above shows a QoS profile configured with Egress Max of 100Mbps. The Egress Max under the Profile section configures the maximum egress bandwidth for all classes of traffic passing through the 10Gb interface.

This would most likely cause heavy congestion, and an outage behavior would be reported by the users.

Resolution

When configuring a QoS profile, the Egress Max should be carefully set, taking the overall bandwidth of the interface into consideration. The intended goal is to restrict class 7 traffic with an Egress Max of 100 and Egress Guaranteed of 10, while all other traffic would take the remaining interface bandwidth.

The screenshot below shows a correct configuration with the Egress Max of the profile set to 10000Mbps, and class7 traffic configured with Egress Max of 100 and Egress Guaranteed of 10:

The QoS interface settings should also be configured with the correct value for Egress Max.

Note: Only desired classes can be defined in the QoS profile. The rest of the traffic would default to class 4.

owner: fkhan