There is provided mechanisms for handling layer 3 measurements of a UE. A method is performed by an access network system. The access network system includes a CU and a DU. The method includes configuring the UE to perform layer 3 measurements. The UE is configured to perform layer 3 measurements according to measurement IDs. A first subset of the measurement IDs is associated with the CU and a second subset of the measurement IDs is associated with the DU. The method includes obtaining a report with a layer 3 measurement from the UE. The report has one of the measurement IDs. The method includes performing, at the CU, an action that depends on the layer 3 measurement in the report only when the measurement ID of the report is one of the measurement IDs in the first subset.