Configuring 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, IP precedence, local precedence, and drop precedence.
Types of priorities
Priorities fall into the following types: priorities carried in packets, and priorities locally assigned for
The packet-carried priorities include 802.1p priority, DSCP precedence, IP precedence, 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 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—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—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-lp—802.1p-to-local priority mapping table.
dscp-dot1p—DSCP-to-802.1p priority mapping table, which is applicable to only IP packets.
dscp-dp—DSCP-to-drop priority mapping table, which is applicable to only IP packets.
dscp-dscp—DSCP-to-DSCP priority mapping table, which is applicable to only IP packets.
The default priority mapping tables (see
priority mapping. In most cases, they are adequate for priority mapping. If a default priority mapping
table cannot meet your requirements, you can modify the priority mapping table as required.
"Appendix B Packet
"Appendix A Default priority mapping
tables") are available for