3-2
The default priority mapping tables (as shown in
Appendix B 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 Switch 4500G 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
.
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
Figure 3-1
.
