— NetFlow is a solution to make an in-depth traffic analysis possible in IP networks. Most of the telecommunication operators have already deployed it, or intend to do so, for network management purposes. While the best description of network state would be achieved by activating NetFlow on all router interfaces at the same time, this would not be a good idea in most of the cases. Then, a natural idea is to select a smaller set of interfaces, while ensuring that a sufficiently large proportion of the total amount of traffic is characterized. A critical factor when selecting these interfaces is traffic variability. Indeed, the decision taken at a given moment has to be robust to future traffic variations, at least on a given period. Mathematical models and algorithms are proposed to tackle this issue. They are based on recent advances in robust optimization to deal with probabilistic constraints. The method is tested on real-life data taken from an international France T´el´eco...