6-12
Quality of Service (QoS): Managing Bandwidth More Effectively
Preparation for Configuring QoS
Table 6-7. Applying QoS Options to Traffic Types Defined by QoS Types
3. If you want to include 802.1p priority settings 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.
5. Before configuring QoS on a switch, refer to the next section, “Planning
a QoS Configuration” for information on per-port QoS resource use.
QoS Options for Prioritizing Outbound Traffic QoS Types
IP-ToS
Precedence
Source-
Port
Option 1:
Configure 802.1p
Priority Rules
Only
Prioritize traffic by sending specific packet
types (determined by QoS type) 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
Option 2:
Configure ToS
DSCP Policies
with 802.1p
Priorities
Prioritize traffic by sending specific packet
types (determined by QoS type) 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
1
In this mode the configuration is fixed. You cannot change the automatic priority assignment
when using IP-ToS Precedence as a QoS type.
