Abstract-- Overlay networks are application layer systems which facilitate users in performing distributed functions such as searches over the contents of other users. An important problem in such networks is that the connections among peers are arbitrary, leading in that way to a topology structure which does not match the underlying physical topology. This topology mismatch leads to large user experienced delays, degraded performance and excessive resource consumption in Wide Area Networks. In this work we propose and evaluate the Distributed Domain Name Order (DDNO) technique which makes unstructured overlay networks topologically-aware. In DDNO, a node devotes half of its connections to nodes that share the same domain-name and the remaining half connections to random nodes. The former connections achieve good performance, because the bulk of the overlay traffic is kept within the same domain, while the latter connections ensure that the topology structure remains connected. Discov...