No worries—VPNs aren’t really that hard to understand. A VPN fits somewhere between
a LAN and WAN and many times may seem just like a WAN link because your computer,
on one LAN, connects to a different, remote LAN, and uses its resources remotely. The
key difference with VPNs is a big one—security! So the definition of connecting a LAN
(or VLAN) to a WAN may sound the same, but a VPN is much more.
Here’s the difference: A typical WAN connects two or more remote LANs together using
someone else’s network like, say, your Internet service provider (ISP), using a router. Your
local host and router see these networks as remote networks and not as local networks
or local resources. This would be a WAN in its most general definition. A VPN actually
makes your local host part of the remote network by using the WAN link that connects you
to the remote LAN. The VPN will make your host appear as though it’s actually local on
the remote network! This means that we now have access to the remote LANs resources,
and that access is very secure.
This may sound a lot like the VLAN definition I just used, and really, the concept is the
same: “Take my host and make it appear local to the remote resources.” Just remember that
for networks that are physically local, using VLANs is a good solution; but for networks
that are physically remote—those than span a WAN—we’d opt for using VPNs instead.
For a simple VPN example, let’s use my home office in Boulder, Colorado. Here, I have
my personal host, but I want it to appear as if it’s on a LAN in my corporate office in Dallas,
Texas, so I can get to my remote servers. VPN is the solution I use for this because I need the
security it provides.
Figure 1.7 shows this example of my host using a VPN connection from Boulder to Dallas,
which allows me to access the remote network services and servers as if my host is right there
on the same VLAN as my servers.
Why is this so important? If you answered, “because my servers in Dallas are secure,
and only the hosts on the same VLAN are allowed to connect to them and use the resources
of these servers,” you nailed it! A VPN allows me to connect to these resources by locally
attaching to the VLAN through a VPN across the WAN. The other option is to open up my
network and servers to everyone on the Internet or another WAN service, in which case my
security goes “poof!” So you can see that it’s a very good thing I have a VPN
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