Cisco Systems OL-4266-08 manual Accepting the Traffic Priority Value on Interswitch Links, 42-116

Chapter 42 Configuring PFC QoS

Common QoS Scenarios

Class Map match-any class-default (id 0)

Match any

Class Map match-all CLASSIFY-PC-SAP (id 2)

Match access-group name CLASSIFY-PC-SAP

Class Map match-all CLASSIFY-VOICE-SIGNAL (id 4)

Match access-group name CLASSIFY-VOICE-SIGNAL

Class Map match-all CLASSIFY-VOICE (id 5)

Match access-group name CLASSIFY-VOICE

To monitor the byte statistics for each traffic class, enter this command:

Router#	show	mls qos ip			gig	5/1
[In]	Policy		map	is IPPHONE-PC			[Out] Default.
QoS Summary		[IP]:			(* -	shared	aggregates, Mod	- switch module)
	Int		Mod	Dir	Class-map DSCP Agg Trust			Fl	AgForward-By	AgPoliced-By
							Id	Id

------------------------------------------------------------------------------------

Gi5/1	5	In CLASSIFY-V		46	1	No	0	0	0
Gi5/1	5	In CLASSIFY-V		24	2	No	0	0	0
Gi5/1	5	In	CLASSIFY-O	0	3	No	0	0	0
Gi5/1	5	In	CLASSIFY-P	25	4	No	0	0	0

Router#

Accepting the Traffic Priority Value on Interswitch Links

The previous section described how to configure the marking operation. This section describes how the upstream devices will use the packet marking.

You must decide whether the incoming traffic priority should be honored or not. To implement the decision, you configure the trust state of the port. When traffic arrives on a port that is set not to trust incoming traffic priority settings, the priority setting of the incoming traffic is rewritten to the lowest priority (zero). Traffic that arrives on an interface that is set to trust incoming traffic priority settings retains its priority setting.

Examples of ports on which it might be valid to trust incoming priority settings are ports that are connected to IP phones and other IP voice devices, video devices, or any device that you trust to send frames with a valid predetermined priority. If you know that appropriate marking is completed when traffic first enters the network, you may also want to set uplink interfaces to trust the incoming priority settings.

Configure ports that are connected to workstations or any devices that do not send all traffic with a predetermined valid priority as untrusted (the default).

In the previous example, you configured QoS to properly mark the voice, SAP, and other best effort traffic at the access layer. This example configures QoS to honor those values as the traffic passes through other network devices by configuring the interswitch links to trust the packet DSCP values.

The previous example had several different traffic classes entering a port and selectively applied different QoS policies to the different traffic types. The configuration was done with the MQC QoS policy syntax, which allows you to apply different marking or trust actions to the different traffic classes arriving on a port.

	Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
42-116	OL-4266-08