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.
- 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
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 priority
command). 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.