The preferred embodiments of the present invention are directed to estimating entropy of origin-destination (OD) data flows in a network. To achieve this, first and second sketches are created corresponding to ingress (i.e. origin) and egress (i.e. destination) flows. The sketches allow estimating entropy associated with data streams as well as entropy associated with an intersection of two or more of the data streams, which provides a mechanism for estimating the entropy OD flows in a network.