1. Implementing Quality of Service (QoS)
Classification and Marking

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Module 4
Markings
Trust Boundaries
NBAR
Class-Based Marking
Pre-Classification
QPPB
Classifying and Marking on Catalyst Switches
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Overview
Classification and marking is critical on the Catalyst switches since it should take place as close to the source as possible
Mapping between Layer 2 and Layer 3 is critical
Multilayer switches understand CoS and IP Precedence and DSCP
Remember: only trunk links can see CoS markings; QoS must be enabled globally
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3560 Examples
Enable QoS Globally
Switch(config)# mls qos
Configuring the trust state on an interface
Switch(config-if)# mls qos trust cos
Classify based on CoS – if there is no CoS value – use the port default which is set to 0 by default
Switch(config-if)# mls qos trust dscp
Classify using DSCP – if the switch is marked with a CoS value; the switch maps the CoS value to a DSCP value using the CoS-to-DSCP map
Switch(config-if)# mls qos trust ip-precedence
Classify using IP Prec– if the switch is marked with a CoS value; the switch maps the CoS value to a DSCP value using the CoS-to-DSCP map
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3560 CoS-to-DSCP Map
Configuring the CoS-to-DSCP map
CoS Value
DSCP Value 1 8 2 16 3 24 4 32 5 40 6 48 7 56
mls qos map cos-dscp dscp1...dscp8
show mls qos maps cos-dscp
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6. 3560 IP Precedence to DSCP Map
Configuring the IP Precedence to DSCP map
mls qos map ip-prec-dscp dscp1...dscp8
show mls qos maps ip-prec-dscp
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3560 Policed-DSCP Map
Configuring the Policed-DSCP map
mls qos map policed-dscp dscp-list to mark-down-dscp
show mls qos maps policed-dscp
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3560 DSCP-to-CoS Map
Configuring the DSCP-to-CoS map
mls qos map dscp-cos dscp-list to cos
show mls qos maps dscp-to-cos
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9. 3560 DSCP-to-DSCP Mutation Map
Configuring the DSCP-DSCP map
mls qos map dscp-mutation
dscp-mutation-name in-dscp to out-dscp
interface interface-id
mls qos trust dscp
mls qos dscp-mutation dscp-mutation-name
show mls qos maps dscp-mutation
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10. Configuring the CoS Value for an Int
Default is 0
mls qos cos {default-cos | override}
show mls qos interface
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11. Configuring Trust with Security
Have the switch trust…but only a phone!
interface interface-id
cdp enable
mls qos trust cos OR mls qos trust dscp
mls qos trust device cisco-phone
show mls qos interface
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12. Have the Phone Override the PC
The IP Phone can overwrite the markings sent by the PC
interface interface-id
switchport priority extend cos cos_value
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DSCP Transparency
Just pass the DSCP settings through
no mls qos rewrite ip dscp
show mls qos interface
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14. Classification and Marking
We will cover VLAN-based QoS in Policing
MQC approach to marking is supported based on access lists for classification (if required)
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