Configuring Priority Mapping; Overview; Introduction To Priorities; Priority Maps - HP MSR4080 Configuration Manual

Configuring priority mapping

Overview

When a packet arrives, a device assigns a set of QoS priority parameters to the packet based on either
a 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 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:
802.1p priority.
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• DSCP.
EXP.
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IP precedence.
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Local precedence.
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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, IP precedence, and EXP. 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. These priorities include the local precedence, drop priority, and user priority, as follows:
Local precedence—Used for queuing. A local precedence value corresponds to an output queue. A
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packet with higher local precedence is assigned to a higher priority output queue to be
preferentially scheduled.
User priority—Precedence that the device automatically extracts from a priority field of the packet
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according to its forwarding path. It is a parameter for determining the scheduling priority and
forwarding priority of the packet. The user priority represents:
The 802.1p priority for Layer 2 packets.
The IP precedence for Layer 3 packets.
The EXP for MPLS packets.

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.
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