Information About Marking Network Traffic - Cisco Catalyst 4500 Series Configuration Manual

Configuring QoS
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Information About Marking Network Traffic

To mark network traffic, you should understand the following concepts:
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Purpose of Marking Network Traffic
Traffic marking is used to identify certain traffic types for unique handling, effectively partitioning
network traffic into different categories.
After the network traffic is organized into classes by traffic classification, traffic marking allows you to
mark (that is, set or change) a value (attribute) for the traffic belonging to a specific class. For instance,
you may want to change the class of service (CoS) value from 2 to 1 in one class, or you may want to
change the differentiated services code point (DSCP) value from 3 to 2 in another class. In this module,
these values are referred to as attributes or marking fields.
Attributes that can be set and modified include the following:
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Benefits of Marking Network Traffic
Traffic marking allows you to fine-tune the attributes for traffic on your network. This increased
granularity helps isolate traffic that requires special handling, and thus, helps to achieve optimal
application performance.
Traffic marking allows you to determine how traffic will be treated, based on how the attributes for the
network traffic are set. It allows you to segment network traffic into multiple priority levels or classes of
service based on those attributes, as follows:
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Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
40-18
"Multi-attribute Marking Support" section on page 40-21
"Hardware Capabilities for Marking" section on page 40-22
"Configuring the Policy Map Marking Action" section on page 40-22
"Marking Statistics" section on page 40-24
"Purpose of Marking Network Traffic" section on page 40-18
"Benefits of Marking Network Traffic" section on page 40-18
"Two Methods for Marking Traffic Attributes" section on page 40-19
CoS value of a tagged Ethernet frame
DSCP/Precedence value in the Type of Service (ToS) byte of IPv4.
QoS group identifier (ID)
DSCP /Precedence value in the traffic class byte of IPv6
Traffic marking is often used to set the IP precedence or IP DSCP values for traffic entering a
network. Networking devices within your network can then use the newly marked IP precedence
values to determine how traffic should be treated. For example, voice traffic can be marked with a
particular IP precedence or DSCP and strict priority can then be configured to put all packets of that
marking into that queue. In this case, the marking was used to identify traffic for strict priority
queue.
Traffic marking can be used to identify traffic for any class-based QoS feature (any feature available
in policy map class configuration mode, although some restrictions exist).
Traffic marking can be used to assign traffic to a QoS group within a switch. The switch can use the
QoS groups to determine how to prioritize traffic for transmission. The QoS group value is usually
used for one of the two following reasons:
Chapter 40 Configuring Quality of Service
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