A network system that includes a first set of network hosts in a first domain and a second set of network hosts in a second domain. Within each of the domains, the system includes several edge switching elements (SEs) that each couple to the network hosts and forward network data to and from the set of network hosts. Within the first domain, the system includes (i) an interior SE that couples to a particular edge SE in order to receive network data for forwarding from the edge SE when the edge SE does not recognize a destination location of the network data and (ii) an interconnection SE that couples to the interior SE, the edge SE, and the second domain through an external network. When the edge SE receives network data with a destination address in the second domain, it forwards the network data directly to the interconnection SE.