CoS Layer 2 >< ToS Layer 3

Just as a reminder , CoS marking (Layer 2) doesn’t “survive” to Layer 3 as the route processor will remark it.

It is why the most of the time a Cos to DSCP rewriting policy must be applied on the input direction of the interface.

AutoQoS Activation

Before enabling AutoQoS , take in mind the following pre-requisites :

  • CEF must be enabled as AutoQoS relies on NBAR which is dependant of CEF.
  • No Policy QoS can be attached to the interface
  • The correct bandwidth statement must be set up on the interface
  • An IP address must be configured on an interface if its speed is less than 768 Kbps
  • The interface can’t be in a shutdown mode

You can the ask why IP Address is an mandatory element ?

It is simply because if your speed links is less than 768 Kbps , then AutoQoS will enable Multilink PPP (MLP)


By default , a class-map will use the match-all criteria so it will tell that you must match all your conditions in your class-map before to classify the traffic .

If you want classify directly when at least one condition is met then use the criteria match-any.

Unclassified traffic will go in the default class.

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