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

QoS Options for Prioritizing Outbound Traffic

QoS Types

 

 

 

 

 

 

IP-ToS

Source-

 

 

Precedence

Port

Option 1:

Prioritize traffic by sending specific packet

Yes 1

Yes

Configure 802.1p

types (determined by QoS type) to different

 

 

Priority Rules

outbound port queues on the switch.

 

 

Only

Rely on VLAN-tagged ports to carry packet

 

 

 

priority as an 802.1p value to downstream

 

 

 

devices.

 

 

Option 2: Configure ToS DSCP Policies with 802.1p Priorities

Prioritize traffic by sending specific packet

No

Yes

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.

 

 

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

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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