Quality of Service (QoS): Managing Bandwidth More Effectively

Preparation for Configuring QoS

2.Select the QoS option you want to use. Table 5-6lists 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

QoS Options for Prioritizing Outbound Traffic

QoS Classifiers

 

 

 

 

 

 

 

 

IP-ToS

IP-

Source

 

 

Precedence

DiffServ

-Port

Option 1:

Prioritize traffic by sending specific packet

Yes1

Yes

Yes

Configure80

types (determined by QoS classifier) to

 

 

 

2.1p Priority

different outbound port queues on the

 

 

 

Rules Only

switch.

 

 

 

 

Rely on VLAN-tagged ports to carry packet

 

 

 

 

priority as an 802.1p value to downstream

 

 

 

 

devices.

 

 

 

 

 

 

 

 

Option 2:

Prioritize traffic by sending specific packet

No

Yes

Yes

Configure

types (determined by QoS classifier) to

 

 

 

ToS DSCP

different outbound port queues on the

 

 

 

Policies

switch.

 

 

 

with 802.1p

Propagate a service policy by reconfiguring

 

 

 

Priorities

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.

1In this mode the configuration is fixed. You cannot change the automatic priority assignment when using IP-ToS Precedence as a QoS classifier.

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.

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