Priority Mapping Tables; Priority Trust Mode On A Port; Priority Mapping Procedure - H3C S5120-SI Configuration Manual

Drop precedence is used for making packet drop decisions. Packets with the highest drop
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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 is to assign to a packet for subsequent packet processing. The
switch provides the following priority mapping tables:
dot1p-dot1p—802.1p-to-802.1p priority mapping table.
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dot1p-dscp—802.1p-to-DSCP priority mapping table.
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dot1p-lp—802.1p-to-local priority mapping table.
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• dscp-dot1p—DSCP-to-802.1p priority mapping table, applicable to only IP packets.
dscp-dscp—DSCP-to-DSCP priority mapping table, applicable to only IP packets.
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dscp-lp—DSCP-to-local priority mapping table, applicable to only IP packets.
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The default priority mapping tables (see the chapter "Appendix A Default priority mapping tables") are
available for 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.

Priority trust mode on a port

The priority trust mode on a port decides which priority is used for priority mapping table lookup. Port
priority was introduced so that you can use it for priority mapping in addition to priority fields carried in
packets. The H3C S5120-SI Switch Series provide the following priority trust modes:
dot1p: Uses the 802.1p priority carried in packets for priority mapping.
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• dscp: Uses the DSCP carried in packets for priority mapping.
undo qos trust: Uses the port priority as the 802.1p priority for priority mapping. The port priority is
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user configurable.
The priority mapping procedure varies with the priority modes. For more information, see
mapping procedure.

Priority mapping procedure

On receiving an Ethernet packet on a port, the switch marks the scheduling priorities (local precedence
and drop precedence) for the Ethernet packet according to the priority trust mode of the receiving port
and the 802.1q tagging status of the packet, as shown in Figure 5.
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Priority