In application layer multicast (ALM), member hosts lack direct knowledge of underlying network topology, which brings some performance penalty. This paper investigates an effective way to rapidly obtain some related topology knowledge, i.e. getting topology hints from existing IP registered resources -- WHOIS database. We further propose a clustering scheme, which can be integrated into the existing ALM solutions. Our proposed scheme can cluster some nearby member hosts no matter when these hosts join the group. Therefore the scheme also solves the join sequences problem in some degree. We also present an application framework of the clustering scheme, and give an application example named HMTP-E that integrates the scheme into HMTP protocol. The experiment results show that the clustering scheme plays a positive role on improving the performance of existing ALM solutions.