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Port Status and Basic Configuration
QoS Pass-Through Mode
■ Any 802.1p tagging on a received packet, or any tag added to a
received frame by the switch via its QoS configuration, will be
preserved as it is transmitted from the switch.
Note As stated earlier, use of this QoS-Passthrough-Mode feature generally assumes
that QoS tagged packets are not being sent through the switch (that is, QoS is
not important). Due to the reduced queue allocation, the receipt of high-
priority (level 6 and 7) packets may in fact suffer packet drops depending on
the traffic load of lower-priority packets.
Priority Mapping With Typical and Optimized QoS Pass-Through
Mode
The switch supports 802.1p VLAN tagging, which is used in conjunction with
the outbound port priority queues to prioritize outbound traffic.
An 802.1Q VLAN tagged packet carries an 802.1p priority setting (0-7). If the
switch receives a tagged packet, it is placed into the appropriate queue based
on the frame's 802.1p priority setting. The mapping with QoS Pass-Through
Mode set to “typical” and “optimized” is as follows:
802.1p Priority
Setting
Prioritization Queue Placement
QoS Pass-Through Mode
set to “Typical”
(4 Queues)
QoS Pass-Through Mode
set to “Optimized”
(2 Queues)
1 1 (low) 2 (normal)
2 1 (low) 2 (normal)
0 or Unspecified 2 (normal) 2 (normal)
3 2 (normal) 2 (normal)
4 3 (medium) 2 (normal)
5 3 (medium) 2 (normal)
6 4 (high) 4 (high)
7 4 (high) 4 (high)