Due to MANET topological routing algorithms are not scalable respect to the number of nodes in the network, we evaluate the potential use of a subnet structure in MANETs. We show scenarios in which a MANET with subnet structure is applicable, present the main technical challenges for the application of this structure and show that a reduction of routing overhead from a factor of N
/k (being N the number of nodes and k the number of subnets) is reachable. In this paper we propose a Subnet Formation and Address Allocation mechanism and evaluate analytically the influence of this proposal on the overhead generated. This solution is only one of the many challenges to fix for putting in use a MANET with subnets structure.