Packet classifiers and evaluation order

The switches covered in this guide provide six types of globally-configured QoS classifiers (match criteria) to select packets for QoS traffic marking.

The switches covered in this guide provide six QoS classifiers (packet criteria) you can use to configure QoS priority.

Classifier search order and precedence

Search order

Precedence

Global QoS classifier

1

1 (highest)

UDP/TCP application type (port)

2

2

Device priority (destination or source IP address)

3

3

IP type of service (ToS): precedence and DSCP bit sets (IP packets only)

4

4

IP protocol (IP, IPX, ARP, AppleTalk, SNA, and NetBeui)

5

5

VLAN ID

6

6

Incoming source-port on the switch

Default

7 (lowest)

The incoming 802.1p priority (present in tagged VLAN environments) is preserved if no global QoS classifier with a higher precedence matches.

Where multiple classifier types are configured, a switch uses the highest-to-lowest search order shown in the table to identify the highest-precedence classifier to apply to any given packet. When a match between a packet and a classifier is found, the switch applies the QoS policy configured for that classifier and the packet is handled accordingly.

NOTE:

On the switches covered in this guide, if the switch is configured with multiple classifiers that address the same packet, the switch uses only the QoS configuration for the QoS classifier that has the highest precedence. In this case, the QoS configuration for another, lower-precedence classifier that may apply is ignored. For example, if QoS assigns high priority to packets belonging to VLAN 100, but normal priority to all IP protocol packets, since protocol priority (4) has precedence over VLAN priority (5), IP protocol packets on VLAN 100 will be set to normal priority.