Managing Switches

Configuring Switch Features

the “normal” outbound port queues. However, with a CoS policy operating in your network, you can determine the outbound priority queue to which a packet is sent.

Policy Options for Extending Traffic Priority Control to OutboundPackets Traveling to Downstream Devices.

If an outbound packet is in an 802.1Q tagged VLAN environment, that is, if the packet is assigned to a tagged VLAN on the outbound port, then the packet carries an 802.1p priority setting that was configured in the switch. This priority setting can range from 0 to 7, and can be used by downstream devices that have up to eight queues. While packets within a switch move only at high or normal priority, they still can carry the 802.1p priority that can be used by downstream devices that have more than two priority levels. Also, if the packet enters the switch with an 802.1p priority setting, CoS can override this setting if configured appropriately.

N o t e

 

If you are not using multiple tagged VLANs in your network, you can still use

 

 

the tagged VLAN feature available in HP Procurve switches by configuring the

 

 

default VLAN as a tagged VLAN.

 

 

 

Priority Settings for Outbound Packets. You can configure a CoS

 

 

 

 

priority of 0 through 7 for an outbound packet. When the packet is sent to a

 

 

port, the CoS priority determines which outbound queue the packet uses.

 

 

Table 13-3. CoS Priority

 

 

 

 

 

 

 

 

QoS Setting

Outbound Port Queue

Operation

 

 

 

 

 

 

0*-3

normal

Packets in this queue leave the port after the

 

 

 

 

high-priority queue is emptied.

 

 

 

 

 

 

4-7

high priority

Packets in this queue leave the port first.

 

 

 

 

 

* Note that in compliance with the 802.1p standard, “0” is ranked as “normal” and is a higher priority than “1” and “2”.

If a packet is not in an 802.1Q tagged VLAN environment, the above settings control only to which outbound queue the packet goes, and no 802.1p priority is added to the packet. However, if the packet is in an 802.1Q tagged VLAN environment, then the above setting is also added to the packet as an 802.1p priority that can be used by downstream devices and applications, as shown in the Priority Mapping Table. For each priority policy setting this table shows:

■The corresponding outbound port queue a packet will use when exiting from any switch covered by the policy

■The corresponding 802.1p priority setting the packet will carry when it leaves the switch

13-13