This work contributes to the theory of entanglement distribution in quantum networks in general, analyzing the generation of long-distance entanglement in particular. It is considered that neighboring stations share one partially entangled pair of qubits, which emphasizes the difficulty of creating remote entanglement in realistic settings. The task is then to design local quantum operations at the stations such that the entanglement present in the links of the whole network gets concentrated between few parties only, regardless of their spatial arrangement. Pure-state and mixed-state quantum...