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Quality of Service
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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 or 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 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 be
assigned based on a general policy, or a detailed examination of the packet.
Detailed examination of the packet needs to take place closer 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 an
end-to-end QoS solution.
Notes: 1. When creating Class Maps and Policy Maps do not use the character ‘&’ in
either name.
2. Currently you may only configure one rule per Class Map.
3. The ingress rate for a Policy Map must be set before setting the egress rate.
4. You must create a Class Map before creating a Policy Map.
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 list of DSCP or IP Precedence values, or a list of VLANs.
3. Use the Policy Map to assign a policy name for a specific manner in which
ingress traffic will be handled.
4. Assign policy rules to each class by "setting" the QoS value for 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.