Priority mapping tables, Priority trust mode on a port, Priority mapping procedure – H3C Technologies H3C S5120 Series Switches User Manual
Page 356: Priority, Trust mode on a port
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Priority Mapping Tables
Priority mapping is implemented with priority mapping tables. The device provides various types of
priority mapping tables, or rather, priority mappings. By looking up a priority mapping table, the device
decides which priority value is to assign to a packet for subsequent packet processing.
z
dot1p-dot1p: 802.1p-to-802.1p priority mapping table.
z
dot1p-dscp: 802.1p-to-DSCP 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-dscp: DSCP-to-DSCP priority mapping table, which is applicable to only IP packets.
z
dscp-lp: DSCP-to-local priority mapping table, which is applicable to only IP packets.
The default priority mapping tables (as shown in
Appendix A Default Priority Mapping Tables
) are
available for priority mapping. Generally, they are sufficient 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. For the
priority mapping purpose, port priority was introduced so that you can use it for priority mapping in
addition to priority fields carried in packets. There are three priority trust modes on H3C S5120-SI series
switches:
z
dot1p: Uses the 802.1p priority carried in packets for priority mapping.
z
dscp: Uses the DSCP carried in packets for priority mapping.
z
undo qos trust: Uses the port priority as the 802.1p priority for priority mapping. The port priority is
user configurable.
The priority mapping procedure varies with the priority modes, as described in the next section
Priority Mapping Procedure
Upon 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