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Configuring priority mapping
Overview
When a packet arrives, a device assigns a set of QoS priority parameters to the packet based on
either of the following:
• A priority field carried in the packet.
• The port priority of the incoming port.
This process is called priority mapping. During this process, the device can modify the priority of the
packet according to the priority mapping rules. The set of QoS priority parameters decides the
scheduling priority and forwarding priority of the packet.
Priority mapping is implemented with priority maps and involves the following priorities:
• 802.11e priority.
• 802.1p priority.
• DSCP.
• IP precedence.
• Local precedence.
Introduction to priorities
Priorities include the following types: priorities carried in packets, and priorities locally assigned for
scheduling only.
Packet-carried priorities include 802.1p priority, DSCP precedence, and I P precedence. These
priorities have global significance and affect the forwarding priority of packets across the network.
For more information about these priorities, see "Appendixes."
Locally assigned priorities only have local significance. They are assigned by the device only for
scheduling. The device supports only local precedence for locally assigned priorities. A local
precedence value corresponds to an output queue. A packet with higher local precedence is
assigned to a higher priority output queue to be preferentially scheduled.
Priority maps
The device provides various types of priority maps. By looking through a priority map, the device
decides which priority value to assign to a packet for subsequent packet processing.
The default priority maps (as shown in Appendix B Default priority maps) are available for priority
mapping. They are adequate in most cases. If a default priority map cannot meet your requirements,
you can modify the priority map as required.
Priority mapping configuration tasks
You can configure priority mapping by using any of the following methods:
• Configuring priority trust mode—In this method, you can configure a port to look up a trusted
priority type (802.1p, for example) in incoming packets in the priority maps. Then, the system
maps the trusted priority to the target priority types and values.
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