3-13 Priority Mapping ConfigurationWhen configuring priority mapping, go to these sections for information you are interested in:z Priority Mapping Overviewz Priority Mapping Configuration Tasksz Configuring Priority Mappingz Displaying and Maintaining Priority Mappingz Priority Mapping Configuration ExamplesPriority Mapping OverviewIntroduction to Priority MappingThe priorities of a packet determine its transmission priority. There are two types of priority: prioritiescarried 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 thenetwork.The locally assigned priorities have only local significance. They are assigned by the device forscheduling only. These priorities include the local precedence and drop precedence, as follows.z 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 bepreferentially scheduled.z Drop precedence is used for making packet drop decisions. Packets with the highest dropprecedence are dropped preferentially.When a packet enters the device from a port, the device assigns a set of QoS priority parameters to thepacket based on a certain priority and sometimes may modify its priority, according to certain rulesdepending on device status. This process is called priority mapping. The priority based on which prioritymapping is performed depends on the priority trust mode configured on the port (see section PriorityTrust Mode on a Port. The set of QoS priority parameters decides the scheduling priority and forwardingpriority of the packet.Priority Mapping TablesPriority mapping is implemented with priority mapping tables. The device provides various types ofpriority mapping tables, or rather, priority mappings. By looking up a priority mapping table, the devicedecides which priority value is to assign to a packet for subsequent packet processing.z dot1p-dp: 802.1p-to-drop priority mapping table.z dot1p-lp: 802.1p-to-local priority mapping table.z dscp-dot1p: DSCP-to-802.1p priority mapping table, which is applicable to only IP packets.z dscp-dp: DSCP-to-drop priority mapping table, which is applicable to only IP packets.z dscp-dscp: DSCP-to-DSCP priority mapping table, which is applicable to only IP packets.
