DSCP is a standards-defined method for determining packet priority through an interface, either into or out of a router.

There are three ways you can use the DSCP field:

Classifier Select a packet based on the contents of some portions of the packet header and apply behavioral policies based on service characteristic defined by the DSCP value

Marker Set the DSCP field based on the traffic profile, as determined by the defined rules

Metering Check compliance to traffic profile using filtering functions

A DSCP value can be mapped to a Class of Service (CoS). Then, for a CoS, rules can be applied to determine priority behavior for packets meeting the criteria for the entire CoS. Multiple DSCP values can be mapped to a single CoS. Rules can also be applied to individual DSCP values.

The default value of DSCP in a packet is 0, which is defined as best-effort. You can determine a higher priority for a traffic type by changing the DSCP value of the packet using a QoS rule or composite operation.

Each QoS list includes a DSCP table. A DSCP lists each possible DSCP value, from 0 to 63. For each value, the list specifies a composite operation. See Pre-configured composite operations for QoS lists.

QoS rules on the list take precedence over the DSCP table. If a QoS rule other than the default matches the packet, the Branch Gateway does not apply the DSCP table to the packet. The Branch Gateway applies only the operation specified in the QoS rule.