— Recently cloud service has been introduced in order for many enterprises to achieve purposes such as improvement in efficiency, cost reduction and revolution in business process. However spoofing or poison attacks on VM inside the cloud cause the deterioration of cloud system and those attacks can make the huddle for spreading the cloud services. Many researches are now under way to solve such problems but most of these seem to be passive and limited in terms of detecting attacks and applying to large scale of networks. In this paper, we propose a defense technique for loss of VM resources against the network attacks called spoofing of poison on OpenStack environment. In our proposal, we use reliable ARP table which makes our proposal more reliable in cloud computing environment. Finally we conclude this paper showing that the proposed mechanism is an effective way to defend the ARP spoofing attack Keywords—ARP, Spoofing, Cloud, OpenStack, Security