Dell PowerConnect M8024 User Manual page 642

Mapping Table Configuration
Each port in the switch can be configured to trust one of the packet fields (802.1p, IP Precedence, or IP
DSCP), or to not trust any packet's priority designation (untrusted mode). If the port is set to a trusted
mode, it uses a mapping table appropriate for the trusted field being used. This mapping table indicates
the CoS queue to which the packet should be forwarded on the appropriate egress port(s). Of course, the
trusted field must exist in the packet for the mapping table to be of any use, so there are default actions
performed when this is not the case. These actions involve directing the packet to a specific CoS level
configured for the ingress port as a whole, based on the existing port default priority as mapped to a
traffic class by the current 802.1p mapping table.
Alternatively, when a port is configured as untrusted, it does not trust any incoming packet priority
designation and uses the port default priority value instead. All packets arriving at the ingress of an
untrusted port are directed to a specific CoS queue on the appropriate egress port(s), in accordance with
the configured default priority of the ingress port. This process is also used for cases where a trusted port
mapping is unable to be honored, such as when a non-IP packet arrives at a port configured to trust the
IP DSCP value.
Use the Mapping Table Configuration page to define how class of service is assigned to a packet.
To display the page, click Quality of Service > Class of Service > Mapping Table Configuration in the
tree view.
The Trust Mode selected on the Mapping Table Configuration page affects how the page displays and
the fields accessible from the page. There are three trust modes available from here:
• Untrusted (None)
• CoS(802.1P)
• IP DSCP
CoS(802.1P) is the default mode, so this is the page that displays when Mapping Table Configuration is
selected from the Class of Service menu page.
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Configuring Quality of Service