Network Virtualization Planning Guide
As virtualization spreads throughout data centers, a single server can now represent dozens of virtual servers which can create complex infrastructures within a virtual environment. When accessing virtual machines within that virtual server, traffic does not leave that server to be inspected by traditional router, firewall and IPS devices located on the physical network. Virtual networks become a necessary tool to facilitate and secure communications between virtual machines and within virtual servers. While hypervisors can offer basic layer2 switching functionality, they do nothing to provide the additional layer of security and traffic management (vFirewall, vRouter) that is required to properly manage and protect a virtual infrastructure.