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10 Quality of Service
This chapter describes the following tasks required to apply QoS policies:
◆ Class Map – Creates a map which identifies a specific class of traffic.
◆ Policy Map – Sets the boundary parameters used for monitoring inbound
traffic, and the action to take for conforming and non-conforming traffic.
◆ Binding to a Port – Applies a policy map to an ingress port.
Overview
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, VLAN lists, CoS values, or source ports. 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.
Note:
You can configure up to 16 rules per class map. You can also include multiple
classes in a policy map.
Note:
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 260).
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