1. A method of collecting, recording, and normalizing network performance data, the method comprising: at least one probe receiving from an agent a first set of performance data collected by the agent in response to synthetic network transactions initiated by the agent, the synthetic network transactions being simulated application transactions, wherein the first set of performance data has at least a first level of network performance information in a set of levels of network performance information in a common data model, wherein the levels of network performance information in the common data model correspond to types of performance data, with the first level of network performance information corresponding to a first type of performance data, and wherein the first set of performance data is collected by the agent into a first management information base; the at least one probe receiving a second set of performance data resulting from passively monitoring network traffic, the second set of performance data comprising a second type of performance data, wherein the second set of performance data has at least a second level of network performance information in the set of levels of network performance information in the common data model, the second level corresponding to the first type of performance data and another type of performance data. wherein the second set of performance data is collected into a second management information base, and wherein the first management information base is different from the second management information base; the at least one probe deriving a third set of performance data related to the common data model based on at least one of the first set of performance data and the second set of performance data, the third set of performance data having a third type of performance data; the at least one probe normalizing at least the first set of performance data and the second set of performance data to create normalized network performance data having a single format; and the at least one probe storing, at a computer, the normalized network performance data in a schema according to the common data model.