1. A method for determining a data path in a network which transmits data packets between IP routers via an IP protocol over a reconfigurable core network, each of said IP routers having at least one network interface for connecting to said core network, at least some of said network interfaces having an associated IP-subnet, said method comprising the steps of: receiving a request to provision a data path from a first IP router to a second IP router; determining a data path from said first IP router to said second IP router taking into account the IP-subnets of network interfaces of IP routers included in said path.