ELSA LANCOM 1000 Office Installationsanleitung Seite 22

Everybody's gone surfing––internet access
You can use this configuration to take your company network onto the information
superhighway using TCP/IP. All you need is a single account with an Internet service
provider (ISP) or online service and a router. All computers on the network can then surf
the Internet via the router.
In this example we are assuming that your Internet service provider is using the PPP
protocol and provides an address which is valid on the Internet and the address of a DNS
server every time it is dialed up (as is usual with online service providers).
But how are the individual computers on the LAN given IP addresses they can use to
access the Internet? By using IP masquerading. In short, this is what happens with IP
masquerading:
The router is the only machine on the LAN to have a valid IP address on the Internet. This
address can be allocated dynamically by the Internet service provider using PPP on dial-
up (see above), for example. The network computers use addresses from a special
address range (Private Address Space, addresses in the tens, for example). The entire
local area network is now "hidden" by IP masquerading behind the registered IP address
of the router. This process has two happy outcomes for the LAN:
All the computers on the local area network can use the IP address of the router to
the outside and so have access to the Internet.
The computers on the local area network become invisible from outside. Only the
IP address of the router will be known on the Internet. IP masquerading also acts as
an effective firewall, preventing access to the network from outside.
Our example:
The network uses the TCP/IP protocol so that the individual workstation computers can
access the Internet. It is up to you which operating system is used on the computers.
Local area network
Router in company
in the company
network
Installation Guide
Router at Network
the ISP at the ISP
ELSA LANCOM Office Router
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