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

ilcram19-2

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

ilcram19-2

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

rewind

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?

ilcram19-2

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