H3C Technologies H3C S10500 Series Switches - Manual (Page 33)

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Priority mapping configuration
NOTE:
Both bridge mode (Layer 2) and route mode (Layer 3) Ethernet ports and subinterfaces support the priority
mapping function. The term
interface in this chapter collectively refers to these types of ports. You can use
the port link-mode command to set an Ethernet port to operate in bridge or route mode (see Layer
2—LAN Switching Configuration Guide).
Priority mapping overview
Introduction to priority mapping
When a packet enters a device, depending on your configuration, the device assigns a set of QoS
priority parameters to the packet based on either a certain priority field carried in the packet or 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 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.”
The locally assigned priorities only have local significance. They are assigned by the device for
scheduling only. These priorities include the local precedence and drop precedence, as follows.
• Local precedence is used for queuing. 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.
• Drop precedence is used for making packet drop decisions. Packets with the highest drop
precedence are dropped preferentially.
Priority mapping tables
Priority mapping is implemented with priority mapping tables. By looking up a priority mapping table,
the device decides which priority value to assign to a packet for subsequent packet processing. The
switch provides the following priority mapping tables:
• dot1p-dp: 802.1p-to-drop priority mapping table.
• dot1p-exp: 802.1p-to-EXP priority mapping table.