2 cissp ® Official Study Guide Eighth Edition

Virtual Desktop Infrastructure (VDI)
A 
virtual desktop infrastructure (VDI)
, sometimes 
called a virtual desktop environment (VDE), hosts a user’s desktop as a VM on a server. 
Users can connect to the server to access their desktop from almost any system, includ-
ing from mobile devices. Persistent virtual desktops retain a custom desktop for the user. 
Nonpersistent virtual desktops are identical for all users. If a user makes changes, the desk-
top reverts to a known state after the user logs off.
Software-Defined Networks (SDNs)
SDNs decouple the control plane from the data 
plane (or forwarding plane). The control plane uses protocols to decide where to send traf-
fic, and the data plane includes rules that decide whether traffic will be forwarded. Instead 
of traditional networking equipment such as routers and switches, an SDN controller han-
dles traffic routing using simpler network devices that accept instructions from the con-
troller. This eliminates some of the complexity related to traditional networking protocols.
Virtual Storage Area Networks (VSANs)
A SAN is a dedicated high-speed network that 
hosts multiple storage devices. They are often used with servers that need high-speed access 
to data. These have historically been expensive due to the complex hardware requirements 
of the SAN. VSANs bypass these complexities with virtualization.
The primary software component in virtualization is a hypervisor. The hypervisor 
manages the VMs, virtual data storage, and virtual network components. As an additional 

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Securely Provisioning Resources 
713
layer of software on the physical server, it represents an additional attack surface. If an 
attacker can compromise a physical host, the attacker can potentially access all of the vir-
tual systems hosted on the physical server. Administrators often take extra care to ensure 
that virtual hosts are hardened.
Although virtualization can simplify many IT concepts, it’s important to remember that 
many of the same basic security requirements still apply. For example, each VM still needs 
to be updated individually. Updating the host system doesn’t update the VMs. Additionally, 
organizations should maintain backups of their virtual assets. Many virtualization tools 
include built-in tools to create full backups of virtual systems and create periodic snap-
shots, allowing relatively easy point-in-time restores.