SmartSwitch Router User Reference Manual 293Chapter 21: QoS Configuration GuidePrecedence for Layer-3 FlowsA precedence from 1 - 7 is associated with each field in a flow. The SSR uses theprecedence value associated with the fields to break ties if packets match more than oneflow. The highest precedence is 1 and the lowest is 7. Here is the default precedence of thefields:• IP: destination port (1), destination IP address (2), source port (3), source IP address (4),TOS (5), interface (6), protocol (7)• IPX: destination network (1), source network (2), destination node (3), source node (4),destination port (5), source port (6), interface (7)Use the qos precedence ip and qos precedence ipx commands to change the defaultprecedence.SSR Queuing PoliciesYou can use one of two queuing policies on the SSR:• Strict priority: Assures the higher priorities of throughput but at the expense of lowerpriorities. For example, during heavy loads, low-priority traffic can be dropped topreserve throughput of control-priority traffic, and so on.• Weighted fair queuing: Distributes priority throughput among the four priorities(control, high, medium, and low) based on percentages.You can set the queuing policy on a per-port basis. The default queuing policy is strictpriority.Traffic Prioritization for Layer-2 FlowsQoS policies applied to layer-2 flows allow you to assign priorities based on source anddestination MAC addresses. A QoS policy set for a layer-2 flow allows you to classify thepriority of traffic from:• A specific source MAC address to a specific destination MAC address (use only whenthe port is in flow bridging mode)• Any source MAC address to a specific destination MAC addressBefore applying a QoS policy to a layer-2 flow, you must first determine whether a port isin address-bridging mode or flow-bridging mode. If a port operates in address-bridgingmode (default), you can specify the priority based on the destination MAC address and aVLAN ID. You can also specify a list of ports to apply the policy.
