5-15
Quality of Service: Managing Bandwidth More Effectively
QoS Traffic Marking
Classifier-Based Traffic Marking
Classifier-based per-port or per-VLAN QoS policies support the following
traffic-marking actions. Note that in addition to globally-configured QoS
traffic marking (802.1p and DSCP prioritization), classifier-based QoS policies
also support IP precedence and rate-limiting.
■ 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 in packet headers to downstream devices.
■ Layer 3 IP precedence-bit marking: Enables the switch to set, change,
and honor prioritization policies by using the IP precedence bits in the
ToS byte of IPv4 packet headers and Traffic Class byte of IPv6 headers.
■ Layer 3 DSCP marking: Enables the switch to set, change, and honor
prioritization policies by using the Differentiated Services (diffserv) bits
in the ToS byte of IPv4 headers and Traffic Class byte of IPv6 headers.
■ Rate-limiting: Enables a port or VLAN interface to allow only the spec-
ified amount of bandwidth to be used for inbound traffic. When traffic
exceeds the configured limit, it is dropped.
For information on how to configure and use classifier-based QoS policies,
see “Advanced Classifier-Based QoS” on page 5-71.
Override of
Global QoS
Settings
After you apply a classifier-based QoS policy on a port or VLAN interface:
■ The 802.1p (CoS) priority and DSCP codepoint marking applied to classi-
fied packets override any 802.1p and DSCP codepoint values that are
globally-configured using the QoS commands, described in “Globally-
Configured QoS” on page 5-16.
■ The rate-limit applied to classified packets overrides any globally config-
ured rate-limit globally-configured with the commands described in the
“Port Traffic Controls” chapter in the Management and Configuration
Guide.
For more information on how classifier-based traffic marking overrides glob-
ally-configured traffic marking, see “Override of Global QoS Settings” on page
5-82.
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