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Figure 2-4 shown a SAN Hierarchy

https://www.youtube.com/watch?v=fOTvN3ZzbOM

2.4.4.2 Intranets and Extranets

One common configuration of a LAN is an intranet. Intranet web servers differ from public
web servers in that the public does not have access to an organization’s intranet without the proper
permissions and passwords. Intranets are designed to be accessed by users who have access
privileges to an organization’s internal LAN. Within an intranet, web servers are installed in the
network, and browser technology is used as the common front end to access information such as
financial data or graphical, text-based data stored on those servers.
An extranet is an intranet that is partially accessible to authorized outsiders. Whereas an
intranet resides behind a firewall and is accessible only to people who are members of the same
company or organization, an extranet provides various levels of accessibility to outsiders. You can
access an extranet only if you have a valid username and password, and your identity determines
which parts of the extranet you can view. Extranets help extend the reach of applications and services
that are intranet-based but that employ extended, secure access to external users or enterprises. This
access is usually accomplished through passwords, user IDs, and other application-level security.
Therefore, an extranet is the extension of two or more intranet strategies with a secure interaction
between participant enterprises and their respective intranets. The extranet maintains control of
access to the intranets within each enterprise in the deployment.
Extranets link customers, suppliers, partners, or communities of interest to a corporate
intranet over a shared infrastructure using dedicated connections, as shown in Figure 2-5.

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