Chapter 14: Quality of Service
The commands described in this section are used to configure Quality o f Service
(QoS) classification criteria and service policies. Differentiated Services (DiffServ)
provides policy-based management mechanisms used for priori tizin g netwo rk
resources to meet the requi remen ts o f s peci fic tra ffic types on a per h op basi s.
Each packet is classified upon e ntry int o the netw ork base d on acce ss 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 differe nt
kinds of forwarding.
All switches or routers that access the Internet rely on class informa tion to pro vide
the same forwarding treatment to packets in the same c lass. C lass infor mation 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 tak e 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 prio ritize the
resources allocated to different traffic classes. The ma nner in w hich an individua l
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 constru ct 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 , foll ow these st eps:
1. Use the “Class Map” to designate a class name for a s pecific ca tegory o f traffic.
2. Edit the rules for each class to specif y a type of traffic based on an acces s 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 clas s by
“setting” the QoS value to be assigned to the ma tching traffic cl ass. The poli cy
rule can also be configured to monitor the average flow and burst rate, and drop
any traffic that exceeds the specified rate, or ju st red uce the D SCP serv ice leve l
for traffic exceeding the specified rate.
5. Use the “Service Policy” to assign a policy map t o a specific interf ace.

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