Quality of Service (QoS): Managing Bandwidth More Effectively

Preparation for Configuring QoS

For more on how QoS operates with the preceding traffic types, see ‘‘Precedence Criteria for QoS Classifiers’’, on page 6-11.)

2.Select the QoS option you want to use. Table 6-7lists the traffic types (QoS classifiers) and the QoS options you can use for prioritizing or setting a policy on these traffic types:

Table 6-7. Applying QoS Options to Traffic Types Defined by QoS Classifiers

QoS Options for Prioritizing Outbound Traffic

 

 

QoS Classifiers

 

 

 

 

UDP/

IP

IP-ToS

IP-

VLAN

Source

 

 

TCP

Device

Precedence

DiffServ

-ID

-Port

Option 1:

Prioritize traffic by sending specific packet types

Yes

Yes

Yes 1

Yes

Yes

Yes

Configure

(determined by QoS classifier) to different

 

 

 

 

 

 

802.1p

outbound port queues on the switch.

 

 

 

 

 

 

Priority

Rely on VLAN-tagged ports to carry packet

 

 

 

 

 

 

Rules Only

priority as an 802.1p value to downstream

 

 

 

 

 

 

 

devices.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Option 2:

Prioritize traffic by sending specific packet types

Yes

Yes

No

Yes

Yes

Yes

Configure

(determined by QoS classifier) to different

 

 

 

 

 

 

ToS DSCP

outbound port queues on the switch.

 

 

 

 

 

 

Policies

Propagate a service policy by reconfiguring the

 

 

 

 

 

 

with

DSCP in outbound IP packets according to

 

 

 

 

 

 

802.1p

packet type. The packet is placed in an outbound

 

 

 

 

 

 

Priorities

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 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.

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