HP 5400ZL - Manual (Page 236)

Quality of Service: Managing Bandwidth More Effectively
QoS Traffic Marking
QoS Traffic Marking
As described in “QoS Operation” on page 6-9, when you apply or reconfigure
QoS actions for selected packets, QoS supports different types of traffic
marking in globally-configured QoS settings and classifier-based per-port or
per-VLAN QoS policies.
Globally-Configured Traffic Marking
If a packet matches one of the globally-configured packet classifiers, QoS
applies one of the following types of traffic marking to the outbound packet:
■ Layer 2 802.1p prioritization: Controls the outbound port-queue prior­
ity for traffic leaving the switch, and (if traffic exits through a VLAN-tagged
port) sends the priority setting with the individual packets to downstream
devices.
■ Layer 3 DSCP marking: Enables the switch to set, change, and honor
prioritization policies by using the Differentiated Services (diff-serv) bits
in the IPv4 ToS byte and IPv6 Traffic Class byte of packet headers.
Layer 2 802.1p Prioritization
By setting a new 802.1p priority value, QoS allows you to control the priority
of outbound packets moving through the switch. The Layer 2 802.1p priority
setting in a packet header determines the outbound port queue to which the
packet is sent.
By default, a Series 3500yl switch has four queues; Series 5400zl switches and
the Series 8212zl switch have eight outbound traffic queues (0 through 7). A
lower-numbered queue has a lower outbound priority; a higher-numbered
queue has a higher outbound priority. Packets are transmitted from the switch
port on the basis of their queue assignment and whether any higher queues
are empty. (To increase bandwidth, you can reconfigure the switch to use four
or two outbound queues; see “QoS Queue Configuration” on page 6-95 for
more information.)
Configuring a new 802.1p priority value allows you to set the outbound priority
queue to which a packet is sent. For example, you can configure an 802.1p
priority of 0 through 7 for an outbound packet. When the packet is sent to a
port, the QoS priority determines the outbound queue to which the packet is
assigned as shown in Table 6-2.
6-14