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Cisco 500 Series

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Configuring Global Settings

The Global Settings page contains information for enabling Trust on the device. Packets entering a QoS domain are classified at the edge of the QoS domain.

To define the Trust configuration:

  1. Click Quality of Service > QoS Advanced Mode > Global Settings.
  2. Select the Trust Mode while the device is in Advanced mode. If a packet CoS level and DSCP tag are mapped to separate queues, the Trust mode determines the queue to which the packet is assigned:
    • CoS/802.1p—Traffic is mapped to queues based on the VPT field in the VLAN tag, or based on the per-port default CoS/802.1p value (if there is no VLAN tag on the incoming packet), the actual mapping of the VPT to queue can be configured in the mapping CoS/802.1p to Queue page.
    • DSCP—All IP traffic is mapped to queues based on the DSCP field in the IP header. The actual mapping of the DSCP to queue can be configured in the DSCP to Queue page. If traffic is not IP traffic, it is mapped to the best effort queue.
    • CoS/802.1p-DSCP—Select to use Trust CoS mode for non-IP traffic and Trust DSCP for IP traffic.
  3. Select the default Advanced mode QoS trust mode (either trusted or untrusted) for interfaces in the Default Mode Status field. This provides basic QoS functionality on Advanced QoS, so that you can trust CoS/DSCP on Advanced QoS by default (without having to create a policy).

    In QoS Advanced Mode, when the Default Mode Status is set to Not Trusted, the Default CoS values configured on the interface are used for prioritizing the traffic arriving on the interface. See the Quality of Service > QoS Advanced Mode > Global Settings page for details.

    If you have a policy on an interface then the Default Mode is irrelevant, the action is according to the policy configuration and unmatched traffic is dropped.
  4. Select Override Ingress DSCP to override the original DSCP values in the incoming packets with the new values according to the DSCP Override Table. When Override Ingress DSCP is enabled, the device uses the new DSCP values for egress queueing. It also replaces the original DSCP values in the packets with the new DSCP values.

    5. NOTE     The frame is mapped to an egress queue using the new, rewritten value, and not by the original DSCP value.

  5. If Override Ingress DSCP was enabled, click DSCP Override Table to reconfigure DSCP. See the DSCP Override Table page for details.