  We consider the problem of generating multipartite entangled states in a
quantum network upon request. We follow a top-down approach, where the required
entanglement is initially present in the network in form of network states
shared between network devices, and then manipulated in such a way that the
desired target state is generated. This minimizes generation times, and allows
for network structures that are in principle independent of physical links. We
present a modular and flexible architecture, where a multi-layer network
consists of devices of varying complexity, including quantum network routers,
switches and clients, that share certain resource states. We concentrate on the
generation of graph states among clients, which are resources for numerous
distributed quantum tasks. We assume minimal functionality for clients, i.e.
they do not participate in the complex and distributed generation process of
the target state. We present architectures based on shared multipartite
entangled Greenberger-Horne-Zeilinger (GHZ) states of different size, and fully
connected decorated graph states respectively. We compare the features of these
architectures to an approach that is based on bipartite entanglement, and
identify advantages of the multipartite approach in terms of memory
requirements and complexity of state manipulation. The architectures can handle
parallel requests, and are designed in such a way that the network state can be
dynamically extended if new clients or devices join the network. For generation
or dynamical extension of the network states, we propose a quantum network
configuration protocol, where entanglement purification is used to establish
high-fidelity states. The latter also allows one to show that the entanglement
generated among clients is private, i.e. the network is secure.
