We consider the problem of interconnecting hosts in spontaneous edge networks composed of various types of wired or wireless physical and link layer technologies. All or some hosts in a spontaneous network can be organized as a multi-hop ad hoc network, connected or not to the global Internet. We argue that this kind of networks requires a more sophisticated approach than standard IP forwarding: communication paths should be managed on a per flow basis, multiple paths need to be maintained to cope with link failures or changing topologies, and the interconnection architecture should provide information on destination reachability. We have designed and implemented Lilith, a prototype of an interconnection node for spontaneous edge networks. We handle network dynamics by establishing MPLS (Multi Protocol Label Switching) label switched paths (LSP) on demand with a reactive ad hoc routing protocol. Interconnection at layer 2.5 makes all the hosts to appear as one single IP subnet so that configuration protocols can use the subnet broadcast for all forms of discovery (addresses, names, services). Performance measurements of the Lilith implementation on Linux show good performance compared with standard IP forwarding and important performance gains when multiple paths are used.