Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers To Configure Quality of Service for Outbound Traffic

Assigning a DSCP Policy on the Basis of the DSCP in IP Packets Received from Upstream Devices

The preceding section describes how to forward a policy set by an edge (or upstream) switch. This option changes a DSCP policy in an outbound IP packet by changing its IP ToS codepoint and applying the priority associated with the new codepoint. (A DSCP policy consists of a differentiated services codepoint and an associated 802.1p priority.) You can use this option concur­ rently with the diffserv 802.1p priority option (above), as long as the DSCPs specified in the two options do not match.

To use this option to configure a change in policy:

1.Identify a DSCP used to set a policy in packets received from an upstream or edge switch.

2.Create a new policy by using qos dscp-map < codepoint > priority < 0 - 7 > to configure an 802.1p priority for the codepoint you will use to overwrite the DSCP the packet carries from upstream. (For more on this topic, refer to “Differentiated Services Codepoint (DSCP) Mapping” on page 15-51.)

3.Use qos type-of-service diff-services < incoming-DSCP> dscp < outgoing- DSCP > to change the policy on packets coming from the edge or upstream switch with the specified incoming DSCP.

(Figure 15-12on page 15-27illustrates this scenario.)

Syntax: qos type-of-service diff-services

Enables ToS diff-services.

qos type-of-service diff-services < current-codepoint> dscp

<new-codepoint >

Configures the switch to select an incoming IP packet carry­ ing the <current-codepoint > and then use the <new-codepoint>to assign a new, previously configured DSCP policy to the packet. The policy overwrites the <current-codepoint>with the

<new-codepoint> and assigns the 802.1p priority specified by the policy. (Use the qos dscp-mapcommand to define the priority for the DSCPs—page15-51.)

no qos type-of-service

Disables all ToS classifier operation. Current ToS DSCP policies and priorities remain in the configuration and will become available if you re-enable ToS diff-services.

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