Chapter 14: Virtual Private Networks—VPN LANCOM Reference Manual LCOS 3.50
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Virtual Private Networks—
VPN
of the Internet and a private one by which the computer can be reached within
the local network.
Static and dynamic IP addresses
Public IP addresses must be applied for and managed, which involves costs.
There is a lso only a limite d number o f public IP addres ses. For this reas on, not
every Internet user has his or her own fixed (static) IP address.
The alternative to static IP addresses are the so-called dynamic IP addresses.
A dynamic IP address is assigned to an Internet user by the Internet Service
Provider (ISP) upon dialling-in, and remains valid for the duration of the
connection. The ISP takes an unused address selected at random from their
pool of IP addresses. This IP address is only temporarily assigned to the user
for the duration of a given connection. When the connection is ended, the IP
address is once again free and the ISP can assign it to another user.
Advantages and disadvantages of dynamic IP addresses
This process has a very important advantage for ISPs: they only need relatively
small pools of IP addresses. Dynamic IP addresses are also favorable for users:
it's not necessary for them to apply for static IP addresses in advance - they
can connect to the Internet immediately. It's also not necessary for them to
manage IP addresses. This saves trouble and costs. The other side of the coin:
A user without a static IP address cannot be addressed directly from the
Internet.
This is a major problem when setting up VPNs. If, for example, Computer A
would like to communicate with Computer B using a VPN tunnel on the
Internet, Computer A needs the remote computer's IP address. If B only has a
dynamic address, A cannot know that address and therefore cannot contact B.
The LANCOM Dynamic VPN offers the answer here.
14.4.2 This is how LANCOM Dynamic VPN works
Let's use two examples to explain how LANCOM Dynamic VPN works
(designations refer to the IP addressing type of the two VPN gateways):
dynamic – static
Many flatrate connections, too, are realised with via dynamic IP
addresses. Every 24 hours or so, the connection is forcibly interrupted.
The new connection is generally assigned with a new and different IP
address.