HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 420

Configuration Guidelines and Limitations Chapter 31 Configuring QoS Send feedback to [email protected] The system provides two predefined class maps for matching broadcast or multicast traffic. These class maps are convenient for creating separate policy maps for unicast and multicast traffic. The predefined class maps are as follows: • class-all-flood The class-all-flood class map matches all broadcast, multicast and unknown unicast traffic (across all CoS values). • class-ip-multicast The class-ip-multicast class map matches all IP multicast traffic. Policy options configured in this class map apply to traffic across all Ethernet CoS values. If you configure this class as a no-drop class, the priority flow control capability is applied across all Ethernet CoS values. In this configuration, pause will be applied to unicast and multicast traffic. If you enable optimized multicast for the above classes, all multicast traffic mapped to the class across all CoS values will be optimized. Note Only one of these predefined classes can be configured in the system QoS policy. Policy for Fibre Channel Interfaces The egress queues are not configurable for native Fibre Channel interfaces. Two queues are available as follows: • A strict priority queue to serve high-priority control traffic. • A queue to serve all data traffic and low-priority control traffic. QoS for Traffic Directed to the CPU The switch automatically applies QoS policies to traffic that is directed to the CPU to ensure that the CPU is not flooded with packets. Control traffic, such as BPDU frames, is given higher priority to ensure delivery. Configuration Guidelines and Limitations Switch resources (such as buffers, virtual output queues, and egress queues) are partitioned based on the default and user-defined system classes. The switch software automatically adjusts the resource allocation to accommodate the configured system classes. To maintain optimal switch performance, follow these guidelines when configuring system classes and policies: • If less than four Ethernet classes are defined, up to two of these classes can be configured as no-drop classes. If more than four Ethernet classes are defined, only one of these classes can be configured as a no-drop class. The default drop class is counted as an Ethernet class. • If priority flow control is enabled on an Ethernet interface, pause will never be applied to traffic with a drop system class. PFC does not apply pause to drop classes and the link-level pause feature is never enabled on an interface with PFC. 31-6 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide OL-16597-01