In our high level overview of QoS we stated that configuring QoS can be complicated. Cisco developed NBAR as the QoS 'autopilot' as one solution to this problem.
More recently, Cisco has developed something called AutoQoS, which also configures QoS settings for you. You can use AutoQoS to a)create policies based on real-time traffic flowing through your router or switch, or b) create predefined voice over IP (VoIP) policies for VoIP traffic flowing through your IOS device.
AutoQoS runs on Cisco IOS routers series 2600 through 7200, and it runs on most Cisco routers with IOS version 12.2(15)T and later. AutoQoS requires that Cisco Express Forwarding (CEF) is enabled. You enable CEF in global configuration mode using the 'ip cef' command.
You will also need 'bandwidth' statements on your interfaces because AutoQoS uses the bandwidth statements when configuring bandwidth limitations for protocols it will be prioritizing. We discuss the 'bandwidth' command here.
If you change your bandwidth statements after configuring AutoQoS, you must rerun AutoQoS. You configure AutoQoS at the interface level, not global level.
Here is how you activate AutoQoS:
cell_pe1(config)# interface Serial0/0 cell_pe1(config-if)# auto qos voip
The above commands will turn on AutoQoS on the serial interface 0/0 for VoIP traffic. You will be surprised by the number of changes this makes to your 'show running-config'. You will find:
a) an access control list defines traffic,
b) a class-map that classifies the traffic into classes (know which traffic to put into each class by the access control list that it matched, the DSCP bit that it matched, or the NBAR protocol that it matched),
c) a policy-map that assigns priorities to the classes, and
d) application of the policy-map to the interface, which affects the traffic.
Here are some associated links on the Cisco Web Site: