Chapter 42 Configuring PFC QoS
Common QoS Scenarios
This is the QoS classification scheme for the traffic arriving on an access layer port:
•Voice traffic: DSCP 46 (highest priority)
•Voice signaling traffic: DSCP 24 (medium priority)
•PC SAP traffic: DSCP 25 (medium priority)
•All other PC traffic: DSCP 0 (best effort)
This classification strategy provides a way to support three different classes of service on the network:
•High priority for voice traffic
•Medium priority for voice signaling and important application traffic
•Low priority for the remaining traffic
You can alter this model to fit other network environments.
PFC QoS can trust received priorities or assign new priorities by applying a QoS policy to the traffic. You configure a QoS policy using the Modular QoS CLI (MQC). In the access switches, the traffic is identified using ACLs, which differentiate the various traffic types entering the port. Once identified, a QoS policy marks the traffic with the appropriate DSCP value. These assigned DSCP values will be trusted when the traffic enters the distribution and core routers.
The port on the access router where the phone and PC are attached has been configured for a voice VLAN (VLAN 110), which is used to separate the phone traffic (subnet 10.1.110.0/24) from the PC traffic (10.1.10.0/24). The voice VLAN subnet uniquely identifies the voice traffic. The UDP and TCP port numbers identify the different applications.
This is the access port access control list (ACL) configuration:
Identify the Voice Traffic from an IP Phone (VVLAN)
ip
permit udp 10.1.110.0 0.0.0.255 any range 16384 32767
Identify the Voice Signaling Traffic from an IP Phone (VVLAN)
ip
permit udp 10.1.110.0 0.0.0.255 any range 2000 2002
Identify the SAP Traffic from the PC (DVLAN)
ip access-list extended CLASSIFY-PC-SAP
permit tcp 10.1.10.0 0.0.0.255 any range 3200 3203 permit tcp 10.1.10.0 0.0.0.255 any eq 3600 any
ip
The next step in configuring the QoS policy is to define the class maps. These class maps associate the identifying ACLs with the QoS actions that you want to perform (marking, in this case). This is the syntax for the class maps:
class-map match-all CLASSIFY-VOICE
match
match
match
match
| Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX |
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