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5-12
Quality of Service (QoS): Managing Bandwidth More Effectively
Preparation for Configuring QoS
2. Select the QoS option you want to use. Table 5-6 lists the traffic types (QoS
classifiers) and the QoS options you can use for prioritizing or setting a
policy on these traffic types:
Table 5-6. Applying QoS Options to Traffic Types Defined by QoS Classifiers
3. If you want 802.1p priority settings to be included in outbound packets,
ensure that tagged VLANs are configured on the appropriate downstream
links.
4. Determine the actual QoS configuration changes you will need to make
on each QoS-capable device in your network in order to implement the
desired policy. Also, if you want downstream devices to read and use
DSCPs in IP packets from the switch, configure them to do so by enabling
ToS Differentiated Service mode and making sure the same DSCP policies
are configured.
QoS Options for Prioritizing Outbound Traffic QoS Classifiers
IP-ToS
Precedence
IP-
DiffServ
Source
-Port
Option 1:
Configure80
2.1p Priority
Rules Only
Prioritize traffic by sending specific packet
types (determined by QoS classifier) to
different outbound port queues on the
switch.
Rely on VLAN-tagged ports to carry packet
priority as an 802.1p value to downstream
devices.
Yes
1
Yes Yes
Option 2:
Configure
ToS DSCP
Policies
with 802.1p
Priorities
Prioritize traffic by sending specific packet
types (determined by QoS classifier) to
different outbound port queues on the
switch.
Propagate a service policy by reconfiguring
the DSCP in outbound IP packets according
to packet type. The packet is placed in an
outbound port queue according to the
802.1p priority configured for that DSCP
policy. (The policy assumes that
downstream devices can be configured to
recognize the DSCP in IP packets and
implement the service policy it indicates.)
Use VLAN-tagged ports to include packet
priority as an 802.1p value to downstream
devices.
No Yes Yes
1
In this mode the configuration is fixed. You cannot change the automatic priority assignment
when using IP-ToS Precedence as a QoS classifier.