Cabletron Systems SmartSwitch Router, User'S Reference Manual

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SmartSwitch Router User Reference Manual 285
Chapter 19: QoS Configuration Guide
SSR Queuing Policies
You can use one of two queuing policies on the SSR:
• Strict priority : Assures the higher priorities of throughput but at the expense of lower
priorities. For example, during heavy loads, low-priority traffic can be dropped to
preserve 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 strict
priority.
Traffic Prioritization for Layer-2 Flows
QoS policies applied to layer-2 flows allow you to assign priorities based on source and
destination MAC addresses. A QoS policy set for a layer-2 flow allows you to classify the
priority of traffic from:
• A specific source MAC address to a specific destination MAC address (use only when
the port is in flow bridging mode)
• Any source MAC address to a specific destination MAC address
Before applying a QoS policy to a layer-2 flow, you must first determine whether a port is
in address-bridging mode or flow-bridging mode. If a port operates in address-bridging
mode (default), you can specify the priority based on the destination MAC address and a
VLAN ID. You can also specify a list of ports to apply the policy.
If a port operates in flow-bridging mode, the user can be more specific and configure
priorities for frames that match both a source AND a destination MAC address and a
VLAN ID. You can also specify a list of ports to apply the policy.
The VLAN ID in the QoS configuration must match the VLAN ID assigned to the list of
ports to which the QoS policy is applied. In a layer-2 only configuration, each port has
only one VLAN ID associated with it and the QoS policy should have the same VLAN ID.
When different VLANs are assigned to the same port using different protocol VLANs, the
layer-2 QoS policy must match the VLAN ID of the protocol VLAN.
Note: In flow mode, you can also ignore the source MAC address and configure the
priority based on the destination MAC address only.
Configuring Layer-2 QoS
When applying QoS to a layer-2 flow, priority can be assigned as follows: