Enterprise QoS Solution Reference Network Design Guide

Chapter 2 Campus QoS Design
Figure 2-13 Access Layer Catalyst 3550 QoS Design Options
Version 3.3
Enable QoS
Globally
Figure 2-14 Distribution Layer Catalyst 3550 QoS Design
Enable QoS
Globally
Catalyst 3550—QoS Considerations and Design
An important point to remember about the Catalyst 3550 is that QoS is disabled by default and must be
enabled globally for configured policies to become effective. While QoS is disabled, all frames/packets
are passed through the switch unaltered (which is equivalent to a trust CoS and trust DSCP state on all
ports). When QoS is globally enabled however, all DSCP and CoS values are (by default) set to 0 (which
is equivalent to an untrusted state on all ports). The example below shows how to verify if QoS has been
enabled or not and also how it can be globally enabled.
Example 2-14 Enabling QoS Globally on the Catalyst 3550
CAT3550#show mls qos
QoS is disabled ! By default QoS is disabled
CAT3550#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
CAT3550(config)#mls qos ! Enables QoS globally for the Cat3550
CAT3550(config)#exit
CAT3550#
CAT3550#show mls qos
QoS is enabled ! Verifies that QoS is enabled globally
CAT3550#
Trusted-Endpoint
Model
AutoQoS–VoIP
Model
PC + SoftPhone +
Scavenger Model
Untrusted Server +
Scavenger Model
IP Phone + PC +
Scavenger (Basic) Model
IP Phone + PC +
Scavenger (Adv) Model
Access-Edges
Trust-DSCP
1P3Q1T
Queuing
1P3Q1T
Queuing
1P3Q1T
Queuing
1P3Q1T
Queuing
1P3Q1T
Queuing
1P3Q1T
Queuing
Interswitch Links
1P3Q2T
Queuing + WRED
Trust-DSCP
Uplinks to
Distribution Layer
Enterprise QoS Solution Reference Network Design Guide
1P3Q2T Queuing +
WRED
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