The interference channel models a wireless network where several source-destination pairs compete for the same resources. This paper considers a 4-node network, where two nodes are sources and the other two are destinations. All nodes are full-duplex and cooperate to mitigate interference. A sum-rate outer bound is derived, which is shown to unify a number of previously derived outer bounds for special cases of cooperation or feedback. The approach is shown to extend to cooperative interference networks with more than two source-destination pairs and for any partial sum-rate. How the derived bound relates to other channel models including cognitive nodes, i.e., nodes that have non-causal knowledge of the messages of some other node, is also discussed. The bound is evaluated in Gaussian noise.