QoS Pre-Classify Question

rewindrewind Member Posts: 40 ■■□□□□□□□□
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!

Comments

  • kryollakryolla Member Posts: 785
    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
    Studying for CCIE and drinking Home Brew
  • ilcram19-2ilcram19-2 Banned Posts: 436
    on your wan interface example

    policy-map child
    class VOICE
    priority xxx
    class avaya-traffic
    bandwidth xx
    policy-map parent
    class class-default
    shape average xxxxxx

    interface Tunnel0
    qos pre-classify

    interface FastEthernet4
    service-policy output parent
  • ilcram19-2ilcram19-2 Banned Posts: 436
    also you need to preclasify the traffic otherwise the service policy wont know what kind of traffic you are priotirizing, qos-preclasify help you mark the packets before they are encapsulated make sure you do qos-preclasify in hub and spoke
  • rewindrewind Member Posts: 40 ■■□□□□□□□□
    Couldn't I just do this:
    ilcram19-2 wrote:
    on your wan interface example

    policy-map child
    class VOICE
    priority xxx
    class avaya-traffic
    bandwidth xx
    policy-map parent
    class class-default
    shape average xxxxxx

    interface Tunnel0
    service-policy output

    interface FastEthernet4
    parent

    Which means I don't need the qos-preclassify command, right?
  • ilcram19-2ilcram19-2 Banned Posts: 436
    nope you will get this message
    class based wighted fair quing no supported on this interface

    also you need to apply pre-clasify for the pre-casification of packets not matter what otherwise your policy wont work becase remeber that a packet is encryted in the vpn proccess, so the pre-clasify will mark the packets so they can apply the service policy and priotirize voice,video or wutever traffic, you can use the show policy-map inter command to troble shoot and see the packets match by the policy u created, remember that this is going over a ipsec or gre tunnel
    thats why you need to use qos preclasify,

    ps. the only implemantion that i have seen and doesnt required the pre-clasify is on ezvpn

    take a closer look to the cisco documentation you had on the link
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