User’s
Manual 125
Chapter 11: Configuring Packet Priority
Class of Service (CoS) allows you to specify which data packets have greater precedence when traffic is
buffered in the switch due to congestion. This switch supports CoS with eight priority queues for each port.
Data packets in a port’s high-priority queue will be transmitted before those in the lower-priority queues. You
can set the default priority for each interface, and configure the mapping of frame priority tags to the switch’s
priority queues.
11.1 Setting the Default Priority for Interfaces
You can specify the default port priority for each interface on the switch. All untagged packets entering the
switch are tagged with the specified default port priority, and then sorted into the appropriate priority queue
at the output port.
Follow these guidelines:
•
This switch provides four priority queues for each port. It uses Weighted Round Robin to prevent head-
of-queue blockage.
•
The default priority applies for an untagged frame received on a port set to accept all frame types (for
example, receives both untagged and tagged frames). This priority does not apply to IEEE 802.1Q
VLAN tagged frames. If the incoming frame is an IEEE 802.1Q VLAN tagged frame, the IEEE 802.1p
User Priority bits will be used.
•
If the output port is an untagged member of the associated VLAN, these frames are stripped of all VLAN
tags prior to transmission.
Command Attributes
Default Priority (CLI Only) – The priority that is assigned to untagged frames received on the specified
interface. (Range: 0 - 7, Default: 0)
Number of Egress Traffic Classes – The number of queue buffers provided for each port.
The information is displayed as “Priority for untagged traffic.”
Configuring Switch Using the Web or CLI
Web
Click Priority – Default Port Priority or Default Trunk Priority
. Modify the default priority for any interface,
then click Apply.
CLI
This example assigns a default priority of 5 to port 3.
Console(config)#
interface ethernet 1/3
Console(config-if)#
switchport priority default 5
Console(config-if)#
end
