Enhancements in Release F.04.08

Configuring Port-Based Priority for Incoming Packets

Configuring Port-Based Priority for Incoming Packets

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Assigning a priority level to traffic on the basis

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of incoming port

 

 

 

 

 

 

 

 

 

When network congestion occurs, it is important to move traffic on the basis of relative importance. However, without prioritization:

■Traffic from less important sources can consume bandwidth and slow down or halt delivery of more important traffic.

■Most traffic from all ports is forwarded as normal priority, and competes for bandwidth with all other normal-priority traffic, regardless of its relative importance.

Traffic received in tagged VLAN packets carries a specific 802.1p priority level (0 - 7) that the switch recognizes and uses to assign packet priority at the outbound port. With the default port-based priority, the switch handles traffic received in untagged packets as "Normal" (priority level = 0).

You can assign a priority level to inbound, untagged VLAN packets. (The switch does not alter the priority level of 802.1p tagged VLAN packets it receives.) Thus, for example, high-priority tagged VLAN traffic received on a port retains its priority in the switch. However, you have the option of configuring the port to assign a priority level to untagged VLAN traffic the port receives.

The Role of 802.1Q VLAN Tagging

An 802.1Q-tagged VLAN packet carries the packet’s VLAN assignment and the 802.1p priority setting (0 - 7). (By contrast, an untagged packet does not have a tag and does not carry a priority setting.) Generally, the switch preserves and uses a packet’s priority setting to determine which outbound queue the packet belongs in on the outbound port. If the outbound port is a tagged member of the VLAN, the packet carries its original priority to the next, downstream device. If the outbound port is not configured as a tagged member of the VLAN, then the tag is stripped from the packet, which then exits from the switch without a priority setting.

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