IPv6 has been developed to deal with the increase in number of hosts in the Internet. IPv6 address can be assigned to any network devices. IPv6 provides new function called SLAAC (Stateless Address Auto Configuration). SLAAC is a significant feature for host itself generating and configuring own addresses to enable communication. But this feature has drawbacks in term of security and management of networks.In this paper, we propose a blocking mechanism for malicious hosts using the feature of RA message in ICMPv6 (Internet Control Message Protocol version 6). It was experimented using Emulab testbed environment. And the result show that it can block malicious hosts successfully.