Quality of Service Options on GRE Tunnel Interfaces

The qos pre-classify command

When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. With the introduction of the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before tunneling and encryption occur.

In the following example, tunnel0 is the tunnel name. The qos pre-classify command enables the QoS for VPNs feature on tunnel0:

Router(config)# interface tunnel0
Router(config-if)# qos pre-classify

Characterizing Traffic for QoS Policies

When configuring a service policy, you first may need to characterize the traffic that is traversing the tunnel. Cisco IOS supports Netflow and IP Cisco Express Forwarding (CEF) accounting on logical interfaces like tunnels. See the NetFlow Services Solutions Guide for more information.

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.

  • Apply the policy to the tunnel interface without qos-preclassify when you want to classify packets based on the pre-tunnel header.
  • 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.
  • Apply the policy to a physical interface and enable qos-preclassify when you want to classify packets based on the pre-tunnel header.
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