/mcpQuality of Service for Voice over IP
Packet Classification
5
QoSVoIP.mif
In general, CAR is more useful for data packets than for voice packets. For example, all data traffic
coming in on an Ethernet interface at less than 1 Mbps can be placed into IP Precedence Class 3, and
any traffic exceeding the 1 Mbps rate can go into Class 1 or be dropped. Other nodes in the network can
then treat the exceeding or nonconforming traffic marked with lower IP Precedence differently. All
voice traffic should conform to the specified rate if it has been provisioned correctly.
The following configuration example shows how to use CAR to classify and mark VoIP packets:
Policy-Based Routing Classification and Marking Example
Policy-based routing (PBR) is another older feature that allows traffic to be routed based on source port
or access list. It also can be used to classify and mark packets. A simple configuration example follows:
Modular QoS Command-Line Interface Classification and Marking Example
The recommended classification and marking method is the Modular QoS Command-Line Interface
(Mod QoS CLI, or MQC) feature, a template-based configuration method that separates the
classification from the policy, allowing multiple QoS features to be configured together for multiple
classes. You use a class map to classify traffic based on various match criteria and a policy map to
Configuration Example 2: Classification and Marking Using CAR
access-list 100 permit udp any any range 16384 32767
access-list 100 permit tcp any any eq 1720
!
interface Ethernet0/0
ip address 10.10.10.1 255.255.255.0
rate-limit input
access-group 100 1000000 8000 8000 conform-action
set-prec-continue 5 exceed-action set-prec-continue 5
In this example, any traffic that matches access list 100 will be set with
IP Precedence 5—meaning that the three most significant bits of the IP
ToS byte are set to 101. Access list 100 here matches the common UDP
ports used by VoIP and the H.323 signaling traffic to TCP port 1720.
Configuration Example 3: Classification and Marking Using PBR
access-list 100 permit udp any any range 16384 32767
access-list 100 permit tcp any any eq 1720
!
route-map classify_mark
match ip address 100
set ip precedence 5
!
interface Ethernet0/0
ip address 10.10.10.1 255.255.255.0
ip policy route-map classify_mark
In this example, any traffic that matches access list 100 will be set with
IP Precedence 5—meaning that the three most significant bits of the IP
ToS byte are set to 101. Access list 100 here matches the common UDP
ports used by VoIP and H.323 signaling traffic to TCP port 1720.