Cisco Systems 3750E manual 36-6, Check if packet came with CoS label tag Yes

Chapter 36 Configuring QoS

Understanding QoS

After classification, the packet is sent to the policing, marking, and the ingress queueing and scheduling stages.

Figure 36-3 Classification Flowchart

						Start
								Trust CoS (IP and non-IP traffic).
				Read ingress interface				Trust DSCP (IP traffic).
IP and				configuration for classification.
non-IP					Trust DSCP or		Trust IP
traffic
					IP precedence		precedence
					(non-IP traffic).		(IP traffic).
									Assign DSCP identical
		Check if packet came							to DSCP in packet.
		with CoS label (tag).
									(Optional) Modify the
			Yes		No
									DSCP by using the
	Use CoS			Assign default					DSCP-to-DSCP-mutation
									map. Use the DSCP
	from frame.			port CoS.
									value to generate
									the QoS label.

Generate DSCP from CoS-to-DSCP map.

Use the DSCP value to generate the QoS label.

Generate the DSCP based on IP precedence in packet. Use the IP-precedence-to-DSCP map. Use the DSCP value to generate the QoS label.

Done Done

Are there any (more) QoS ACLs	No
configured for this interface?
Yes
Read next ACL. Is there	No
a match with a "permit" action?
Yes

Check if packet came with CoS label (tag).

	Yes		No
Use the CoS value to		Assign the default port
generate the QoS label.		CoS and generate a
		DSCP from the
		CoS-to-DSCP map.

Assign the DSCP or CoS as specified		Assign the default
by ACL action to generate the QoS label.		DSCP (0).
	Done

Generate the DSCP by using

the CoS-to-DSCP map.

Done

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Catalyst 3750-E and 3560-E Switch Software Configuration Guide

36-6 OL-9775-02