Advanced Traffic Management Guide K/KA/KB.15.15

Classifier-based policies take precedence over, and may override, globally-configured QoS settings
that apply to all traffic on the switch.
Classifier-based QoS policies provide greater control for managing network traffic. Using multiple
match criteria, you can finely select and define the classes of traffic that you want to manage.
QoS-specific policy actions determine how you can handle the selected traffic.
See the Advanced Traffic Management Guide.
Classifier-based QoS model
Classifier-based QoS configuration consists of the following general steps:
1. Classify the traffic that you want to manage by configuring a class.
2. Configure a QoS policy in which you specify the QoS actions to execute on each class of
traffic.
3. Assign the QoS policy to a port or VLAN (inbound only) interface.
NOTE: Classifier-based QoS operation supports all globally-configured packet classification
criteria (except for Source-port and Layer-3 protocol) and traffic marking functions, and provides
additional QoS actions on a per-port and per-VLAN basis.
• Classifier-based match criteria on inbound IPv4/IPv6 traffic include:
• IP source address (IPv4 and IPv6)
• IP destination address (IPv4 and IPv6)
• IP protocol (such as ICMP or SNMP)
• Layer 3 IP precedence bits
• Layer 3 DSCP codepoint
• Layer 4 TCP/UDP application port (including TCP flags)
• VLAN ID
• Classifier-based QoS policy actions on matching IPv4/IPv6 packets are as follows:
• Setting the Layer 2 802.1p priority value (class of service) in VLAN-tagged and untagged
packet headers
• Setting the Layer 3 IP precedence bits
• Setting the Layer 3 Differentiated Services Codepoint (DSCP) bits
• Rate limiting inbound traffic on port and VLAN interfaces
Override of global QoS settings
After you apply a QoS policy to an interface, the classifier-based settings configured by QoS
actions in the policy override any 802.1p CoS or DSCP codepoint values that were
globally-configured on the switch to mark packets using the QoS commands.
If you use a classifier-based QoS configuration along with globally-configured QoS commands,
the order of precedence in which 802.1p priority, IP precedence, and DSCP settings mark selected
packets is as follows, from highest (1) to lowest (9):
Table 23 Order of precedence for classifier-based QoS over global QoS
QoS featurePrecedence order
Classifier-based port-specific policy1
Classifier-based VLAN-specific policy2
Globally-configured TCP/UDP priority3
Classifier-based QoS model 255