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Chapter 14: Quality of Service
The commands described in this section are used to configure Quality of Service
(QoS) classification criteria and service policies. Differentiated Services (DiffServ)
provides policy-based management mechanisms used for prioritizing network
resources to meet the requirements of specific traffic types on a per hop basis.
Each packet is classified upon entry into the network based on access lists, IP
Precedence, DSCP values, or VLAN lists. Using access lists allows you select traffic
based on Layer 2, Layer 3, or Layer 4 information contained in each packet. Based
on configured network policies, different kinds of traffic can be marked for different
kinds of forwarding.
All switches or routers that access the Internet rely on class information to provide
the same forwarding treatment to packets in the same class. Class information can
be assigned by end hosts, or switches or routers along the path. Priority can then be
assigned based on a general policy, or a detailed examination of the packet.
However, note that detailed examination of packets should take place close to the
network edge so that core switches and routers are not overloaded.
Switches and routers along the path can use class information to prioritize the
resources allocated to different traffic classes. The manner in which an individual
device handles traffic in the DiffServ architecture is called per-hop behavior. All
devices along a path should be configured in a consistent manner to construct a
consistent end-to-end QoS solution.
Notes: 1. You can configure up to 16 rules per Class Map. You can also include
multiple classes in a Policy Map.
2.
You should create a Class Map before creating a Policy Map. Otherwise, you
will not be able to select a Class Map from the Policy Rule Settings screen
(see page 14-6).
Configuring Quality of Service Parameters
To create a service policy for a specific category or ingress traffic, follow these steps:
1. Use the “Class Map” to designate a class name for a specific category of traffic.
2. Edit the rules for each class to specify a type of traffic based on an access list, a
DSCP or IP Precedence value, or a VLAN.
3. Use the “Policy Map” to designate a policy name for a specific manner in which
ingress traffic will be handled.
4. Add one or more classes to the Policy Map. Assign policy rules to each class by
“setting” the QoS value to be assigned to the matching traffic class. The policy
rule can also be configured to monitor the average flow and burst rate, and drop
any traffic that exceeds the specified rate, or just reduce the DSCP service level
for traffic exceeding the specified rate.
5. Use the “Service Policy” to assign a policy map to a specific interface.
14-1