3com 5500-ei pwr Instrução De Instalação

 

1-8 

Local precedence is a locally significant precedence that the device assigns to a packet. A 

local precedence value corresponds to one of the eight hardware output queues. Packets 

with the highest local precedence are processed preferentially. As local precedence is 

used only for internal queuing, a packet does not carry it after leaving the queue.  

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.  

 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 

Table 1-5 802.1p priority-to-local precedence mapping table 

0 2 

1 0 

2 1 

3 3 

4 4 

5 5 

6 6