Summary 247
The configuration applies dot1q subinterfaces to each Gigabit Ethernet interface separately
to achieve load balancing without using port channeling.
The QoS mapping configuration consists of prioritizing IP precedence values 4 and 5 with
50 percent of the effective bandwidth of interfaces Gigabit Ethernet 1, 3, and 4. By default,
Cisco IP Phones assign an IP precedence value of 5, which maps to queue class 2, to voice
traffic (thus the reasoning for using a higher WRR weight for this queue class).
Furthermore, interface Gigabit Ethernet 1 connected to the core switch applies a rate-limiting
configuration. The rate limiting limits all egress traffic flowing to the core to 100 Mbps.
Summary
The Catalyst 4000 IOS Family of switches provides for a wide range of QoS features. The
switch bases classification, marking, policing, and output scheduling on not only DSCP
values but also CoS values. The fine granularity of QoS features and configuration options
allow for these switches to reside in either the core, distribution, or access layer of the
campus network topology. You can summarize QoS feature support on the Catalyst 4000
IOS Family of switches discussed in the first part of the chapter as follows:
• At the time of publication, the Catalyst 4000 IOS Family of switches includes the
Catalyst Supervisor Engines III and IV in a Catalyst 4000 or 4500 series chassis.
• Support exists for classification, reclassification, marking, and output scheduling.
• QoS packet processing occurs in hardware to achieve line-rate performance.
• 1022 ingress and 1022 egress policers applied as aggregate or individual policers are
supported.
• Each interfaces uses four transmit queues for output scheduling.
• Sharing and traffic shaping are configurable per transmit queue.
The Catalyst 2948G-L3 and 4908G-L3 and the Catalyst 4000 Layer 3 services module,
WS-X4232-L3, act only as QoS forwarding switches. For QoS features such as trusting and
marking, these switches rely solely on externally connected switches or routers. You can
summarize the QoS feature support on these switches discussed in the second part of this
chapter as follows:
• Support exists for classification and output scheduling.
• Classification is determined by IP precedence only.
• Output scheduling uses WRR to differentiate service.
• Rate limiting is configurable per interface on ingress or egress.
• Traffic shaping is configurable per interface on egress only.
• Port-channel interfaces do not support any QoS features.
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