Global QoS classifier precedence: 3

The global IP Type-of-Service classifier enables you to classify and mark IP packets according to the following modes:

IP-precedence mode

All IP packets generated by upstream devices and applications include a precedence bit set in the ToS/Traffic Class byte. In IP-precedence mode, the switch uses the precedence bits to compute and assign the corresponding 802.1p priority.

IP Differentiated Services (Diffserv) Mode
The Diffserv mode uses the codepoints set in IP packets by upstream devices and applications to assign an 802.1p priority to packets. You can use Diffserv mode to mark packets in the following ways:
  • Assign a new DSCP policy: A policy includes both a codepoint and a corresponding 802.1p priority. This option selects an incoming IP packet on the basis of its codepoint and assigns a new codepoint and corresponding 802.1p priority. Use the qos dscp-map command to specify a priority for any codepoint.
  • Assign an 802.1p priority: This option reads the DSCP of an incoming IP packet and, without changing this codepoint, assigns the 802.1p priority to the packet, as configured in the DSCP Policy Table. This means that a priority value of 0 - 7 must be configured for a DSCP before the switch can perform a QoS match on the packet's DSCP bits.

Prerequisite: A DSCP codepoint must have a preconfigured 802.1p priority (0 - 7) before you can use the codepoint to mark matching packets. If a codepoint you want to use shows No-override in the Priority column of the DSCP Policy table (show qos dscp-map command), you must first configure a priority for the codepoint before proceeding (qos dscp-map prioritycommand). Some 802.1p priorities are assigned by default to well-known DSCP codepoints, such as the "Assured Forwarding" and "Expedited Forwarding" codepoints.

Unless IP-Precedence mode and Diffserv mode are both disabled (the default setting), enabling one automatically disables the other.