A device includes: a processor configured to execute instructions in a memory, wherein, the instructions are configured to cause the processor to: select a first network group from among network groups, wherein the first network group is selected from among the network groups based on numbers of global links connecting the network groups, respectively; obtain a first list of network groups, among the network groups, that are not connected to the first network group; select a second network group and a third network group from among the network groups in the first list based on connections between the network groups in the first list; and based on the selecting of the first, second, and third network groups, form a topology including global links connecting the first network group, the second network group, and the third network group each to each other.