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Priority mapping configuration
This chapter includes these sections:
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Priority mapping configuration task list
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Displaying and maintaining priority mapping
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Priority mapping configuration examples
Priority mapping overview
Introduction to priority mapping
When a packet enters a device, the device assigns a set of QoS priority parameters to the packet based
on a certain priority field carried in the packet or the port priority of the incoming port, depending on
your configuration. This process is called priority mapping. During this process, the device may modify
the priority of the packet depending on device status. The set of QoS priority parameters decides the
scheduling priority and forwarding priority of the packet.
Priority mapping is implemented with priority mapping tables and involves priorities such as 802.1p
priority, DSCP, EXP, IP precedence, local precedence, and drop precedence.
Introduction to priorities
Priorities fall into the following types: priorities carried in packets and priorities locally assigned for
scheduling only.
The packet carried priorities include 802.1p priority, DSCP precedence, IP precedence, EXP, and so on.
These priorities have global significance and affect the forwarding priority of packets across the network.
For more information about these priorities, see the chapter “Appendix B Introduction to packet
precedences.”
The locally assigned priorities have only local significance. They are assigned by the device for
scheduling only. These priorities include the local precedence and drop precedence.
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Local precedence is used for queuing. The S5120-SI switches map eight local precedence values to
four output queues as shown in Table 3. For more information about queue scheduling, see the
chapter “Congestion management configuration.”
Table 3
Local precedence and queue map
Local precedence
Queue ID
0, 1
0
2, 3
1
4, 5
2
6, 7
3