Systems, methods, and non-transitory computer-readable storage media for verifying service contracts by measuring rates of out-of-contract traffic. The method is discussed in terms of a system implementing the method. The system determines, based on packet markings, a number of network packets that are classified as out-of-contract by a network device, wherein the packet markings indicate a classification associated with respective network packets. The packet markings can be Differentiated Services Code Point markings Moreover, the classification associated with respective network packets can include a class of service and at least one of an in-contract status and an out-of-contract status. Next, the system measures network packets sent to the network device. Finally, the system determines how the network device is configured to classify incoming packets based on the number of network packets that are classified as out-of-contract by the network device and the network packets sent to the network device.