Classifying Traffic by Layer 3 or Layer 4 Characteristics

ACL Rules

You can, alternately, configure the switch to classify traffic by the IP characteristics of packets, instead of 802.1p tag priority, physical port priority, or other layer 2 characteristics.

To assign priorities to packets by their IP characteristics, you create a rule in an access control list (ACL). The rule can:

• Set an ACL rule priority
• Use the DiffServ code point
• Mask the three least significant bits of the DSCP. The switch recognizes the remaining bits as the IP precedence field.
• Replace the existing DSCP with a DSCP that you specify
• Use the layer 2 priority

You can specify the TCP/IP traffic that you want the rule to apply to. The rule can apply to traffic with a specific:

• IP destination address
• IP source address
• IP Protocol
• Destination TCP or UDP port
• Source TCP or UDP port

The priority that is specified by an ACL takes precedence over all other priorities. Because of this precedence, the switch determines whether a rule in an ACL exists for an IP packet in the final stage of classification. If an ACL exists, the priority associated with the ACL replaces the current priority of the frame.

For information on how to set a rule in an ACL, see "Setting Up an ACL Rule" later in this chapter.