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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 3 QoS in an AVVID-Enabled Campus Network
Selecting a Distribution-Layer Switch
Modifying the CoS-to-DSCP Mapping
There are 8 CoS labels and 64 possible DSCP labels. To trust the CoS markings, the default
CoS-to-DSCP mapping table must be modified to equate CoS 3 (VoIP control traffic) to AF31, CoS 5
(VoIP bearer traffic) to EF, and CoS 4 to AF41.
Step 1
The default CoS-to-DSCP mapping is as follows:
3550G-Dist#show mls qos maps
Cos-dscp map:
cos: 0 1 2 3 4 5 6 7
--------------------------------
dscp: 0 8 16
24 32 40 48 56
Change the default CoS-to-DSCP mapping so that CoS 5 = EF and CoS 3 = AF31 and CoS 4 = AF41.
3550G-Dist(config)#mls qos map cos-dscp 0 8 16
26 34 46 48 56
Enabling Priority Queuing
To enable priority queuing, do the following:
Step 1
Specify the interface range.
3550G-Dist(config)#interface range g 0/1 - 12
Step 2
Specify the priority queue.
3550G-Dist(config-if-range)#priority-queue out
Step 3
Move the CoS 5 traffic to queue 4, which is the priority queue for the Catalyst 3500 family.
3550G-Dist(config-if-range)#wrr-queue cos-map 4 5
Configuring ACLs
There are times when classification of traffic by the access-layer switch is required. The Catalyst 3550
has a powerful set of features that allow us to classify traffic as it enters the network. The following
configuration illustrates how to classify VoIP bearer and control traffic with the Catalyst 3550 as it
enters the network.
Step 1
Create ACLs to identify the traffic.
3550G-Dist(config)#ip access-list extended GOLD-DATA
3550G-Dist(config-ext-nacl)#remark Match IP Address of the application server
3550G-Dist(config-ext-nacl)#permit ip any host 192.168.100.1
3550G-Dist(config-ext-nacl)#permit ip host 192.168.100.1 any
3550G-Dist(config)#ip access-list extended VOICE
3550G-Dist(config-ext-nacl)#remark Match the UDP ports that VoIP Uses for Bearer Traffic
3550G-Dist(config-ext-nacl)#permit udp any any range 16384 32767
3550G-Dist(config)#ip access-list extended VOICE-CONTROL
3550G-Dist(config-ext-nacl)#remark Match VoIP Control Traffic
3550G-Dist(config-ext-nacl)#remark SCCP