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C
14
HAPTER
Q
S
UALITY OF
ERVICE
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.
14-1
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