1-7
Priority trust mode
After a packet enters a switch, the switch sets the 802.1p priority and local precedence for the packet
according to its own capability and the corresponding rules.
1) For a packet carrying no 802.1q tag
When a packet carrying no 802.1q tag reaches the port of a switch, the switch uses the port priority as
the 802.1p precedence value of the received packet, searches for the local precedence corresponding
to the port priority of the receiving port in the 802.1p-to-local precedence mapping table, and assigns
the local precedence to the packet.
2) For an 802.1q tagged packet
When an 802.1q tagged packet reaches the port of a switch, you can use the
priority trust
on the
receiving port to configure the port to trust packet priority or use the
priority
command on the receiving
port to configure the port to trust port priority. By default, port priority is trusted and the priority of a port
is 0.
z
Trusting port priority
In this mode, the switch replaces the 802.1p priority of the received packet with the port priority,
searches for the local precedence corresponding to the port priority of the receiving port in the
802.1p-to-local precedence mapping table, and assigns the local precedence to the packet.
z
Trusting packet priority
In this mode, the switch searches for the local precedence corresponding to the 802.1p priority of the
packet in the 802.1p-to-local precedence mapping table and assigns the local precedence to the
packet.
Table 1-5
shows the default 802.1p priority-to-local precedence mapping table. You can modify the
default mapping tables at the CLI. For detailed configuration procedure, refer to
Configuring the
Mapping between 802.1p Priority and Local Precedence
.
Table 1-5
802.1p priority-to-local precedence mapping table
802.1p priority
Local precedence
0 2
1 0
2 1
3 3
4 4
5 5
6 6
7 7
Protocol Priority
Protocol packets generated by a switch carry their own priority. You can set a new IP precedence or
DSCP precedence for the specific type of protocol packets to implement QoS.
