Methods and apparatus are disclosed for processing local area network diagnostic data obtained in respect of a local area network (LAN). The method includes identifying, from local area network diagnostic data obtained in respect of the LAN, a set of data units including a first and an associated second data unit having a predetermined relationship; updating the first data unit of the set to include an indication that the associated second data unit of the set has been identified; and sending the updated first data unit without the associated second data unit from the LAN for performance analysis at a remote network diagnostic device outside the LAN.