A method is provided of planning routes and allocating route identifiers in a managed frame-forwarding network. The network comprises a plurality of nodes interconnected by links, with each node being arranged to forward data frames according to a combination of an identifier and a network address carried by a received data frame and forwarding instructions stored at the node. A first step of the method identifies a sub-set of nodes which are core nodes of the network. The remaining nodes are termed outlying nodes. A spanning tree is then built off each of the identified core nodes, with the spanning tree stopping one link short of any other core node. Each spanning tree defines a loop-free path between a core node at the root of the spanning tree and a set of outlying nodes. Connections are planned between roots of the spanning trees and a different identifier is allocated to each planned connection between a pair of spanning trees.