This is the number of times an IS-IS control PDU with a max area address field different to that for this system has been received. It flags a neighbor whose configured maximum-number-of-area-addresses parameter does not match this router's own setting, a subtle IS-IS compatibility parameter rarely touched from its default but capable of causing adjacency problems if one side was reconfigured without updating the other. For example, an admin who increased the max-area-addresses setting on one router to support multi-area attachment without updating a directly connected neighbor would see this counter climb on that specific circuit until both sides are reconciled.