QoS Pre-Classify Question

rewind

From Cisco.com: http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtml

"Where Do I Apply the Service Policy?

You can apply a service policy to either the tunnel interface or to the underlying physical interface. The decision of where to apply the policy depends on the QoS objectives. It also depends on which header you need to use for classification.

1) Apply the policy to the tunnel interface without qos-preclassify when you want to classify packets based on the pre-tunnel header.

2) Apply the policy to the physical interface without qos-preclassify when you want to classify packets based on the post-tunnel header. In addition, apply the policy to the physical interface when you want to shape or police all traffic belonging to a tunnel, and the physical interface supports several tunnels.

3) Apply the policy to a physical interface and enable qos-preclassify when you want to classify packets based on the pre-tunnel header"

It seems like 1 and 3 both do the same thing. I'm having trouble seeing a reason for ever needing the qos-preclassify command. Can anybody lend some insight here?

Thanks!

kryolla

This is taken from the Cisco Docs

Alternately, you may want to classify traffic based on values other than IP precedence or DSCP. For example, you may want to classify packets based on IP flow or Layer 3 information, such as source and destination IP address. To do this, you must use the QoS for VPNs feature. This feature is enabled with the qos pre-classify