Quality of Service
QoS Advanced Mode
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•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 traf fic is not IP traffic, it i s mapped to th e best effor t
queue.
•CoS/802.1p-DSCP—Select to use Trust CoS mode for non-IP traffic and
Trust DSCP for IP traffic.
STEP 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.
STEP 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.
NOTE The frame is mapped to an egress queue using the new, rewritten
value, and not by the original DSCP value.
STEP 5 If Override Ingress DSCP was enabled, click DSCP Override Table to
reconfigure DSCP. See the DSCP Override Table page for details.
Configuring Out-of-Profile DSCP Mapping
When a policer is assigned to a class maps (flows), you can specify the action to
take when the amount of traffic in the flow(s) exceeds the QoS-specified limits.
The portion of the traffic that causes the flow to exceed its QoS limit is referred to
as out-of-profile packets.