Guidelines for Configuring QoS over 802.3ad Link Aggregation Groups
When you configure QoS over 802.3ad LAGs, be sure to consider the following behaviors:
- QoS profiles cannot be attached to Ethernet ports if the port is a member of a LAG. In typical QoS configurations, the Ethernet interface is considered the root of the interface hierarchy. When you configure QoS for 802.3ad link aggregation, the LAG interface is considered the root of the interface hierarchy.
- You cannot configure hierarchical QoS for IP configured directly over a LAG interface.
- You cannot obtain QoS information or statistics for IP interfaces stacked over a LAG interface using any of the show commands for QoS. Instead, the show qos scheduler-hierarchy command is designed to find the interface hierarchy rooted at the specified interface and report all scheduler nodes and queues managed by those interfaces. The typical defaults in QoS profiles such as ethernet-default and atm-default specify the "ip queue traffic-class best-effort" rule, so those queues are reported in the interface hierarchy. The lag-default QoS profile does not specify this rule by default.
- Do not attach QoS profiles to IP or VLAN subinterfaces in a LAG that contain downreferences (that is, rules for S-VLAN or Ethernet nodes or queues). QoS profiles attached at subinterfaces above a LAG that also include downreference create an asymmetric scheduler hierarchy. For example, one Ethernet port might be shaped and not another.
Also, if the QoS profile specifies only Ethernet, then the traffic sent to the subinterface might be only partially affected by the QoS profile, or not at all. The traffic can be allocated to another port entirely.