Qos Pass-Through Mode On The Series 2800 And 4100Gl Switches; General Operation - ProCurve 2626 Management And Configuration Manual

QoS Pass-Through Mode on the Series
2800 and 4100gl Switches
QoS Pass-Through mode is designed to enhance the performance of line-rate
traffic transfers through the Series 2800 and 4100gl switches. This feature
should only be used in environments where Quality of Service (QoS) is not of
major importance, but where lossless data transfers are key. This command
disables any discrimination of QoS queues for traffic, consolidating packet
buffer memory to provide line-rate flows with no loss of data.

General Operation

The port buffering design for the switch has been optimized for gigabit-to-
gigabit traffic flows. For this reason, some flows from Gigabit-to-100Base or
even 100Base-to-10Base may not perform as well as would be expected. The
QoS Pass-Through mode enhancement can provide a significant performance
improvement for high-bandwidth traffic flows through the switch, particularly
when running traffic flows from 1000Base to either 100Base or 10Base connec­
tions.
QoS Pass-Through mode is OFF by default, and must be enabled via the
"config" context of the CLI by entering the CLI command qos-passthrough-
mode, followed by write memory and rebooting the switch.
QoS Pass-Through mode, when enabled, results in the following general
changes to switch operation:
Alters the switch's default outbound priority queue scheme from four
■
queues (low, normal, medium, and high), to two queues (normal &
high).
Optimizes outbound port buffers for a two-queue scheme.
■
■ All packets received with an 802.1p priority tag of 0 to 5 (low, normal,
or medium priorities), or tagged by the switch's QOS feature, will be
serviced by the (now larger) "normal" priority queue.
■ All packets received with an 802.1p priority tag of 6 or 7 (high priority),
or tagged by the switch's QoS feature, will be serviced by the "high"
priority queue.
■ High priority packets sourced by the switch itself, such as Spanning
Tree packets, will be serviced in the "high" priority queue.

QoS Pass-Through Mode on the Series 2800 and 4100gl Switches

Port Status and Basic Configuration
10-25