ELSA LANCOM Business LC-4X00, Manual

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Operating modes and functions
ELSA LANCOM Business
37
The hiding place—IP masquerading (NAT, PAT)
One of today's most common tasks for routers is connecting the numerous workstation
computers in a LAN to the network of all networks, the Internet. Everyone should have
the potential to access the WWW from his workstation and be able to fetch bang up-to-
date information for his work.
But this provokes objections from the network manager responsible for the security of
data on the company's network: Every workstation computer on the WWW? Surely this
means that anyone can get in from outside?—Not true!
IP masquerading provides a hiding place for every computer while connected with the
Internet. Only the router module of the unit and its IP address are visible on the Internet.
The IP address can be fixed or assigned dynamically by the provider. The computers in
the LAN then use the router as a gateway so that they themselves cannot be detected.
To do this, the router separates Internet and intranet, as if by a wall. Therefore, IP
masquerading is also called a “firewall function“.
The use of IP masquerading is set individually for each route in the routing table. The
routing table can be found in the
ELSA LANconfig in the 'TCP/IP' configuration section on
the 'Routing' tab, or in the
/Setup/IP-router-module/IP-routing-table
menu.
For further information, see the 'IP Routing: IP masquerading' section.
Call charge management
The capability of the router to automatically establish connections to all required remote
stations and close them again when no longer required provides users with extremely
convenient access to the Internet, remote networks and individual computers. However,
incorrect configuration of the router (such as badly configured filters) for data transfer via
ISDN dial-up connections or excessive use of the features provided (continual Internet
surfing, for example) can result in high telephone charges.
Charge-based connection limits
In order to limit these charges, the software has long offered the option of specifying a
ceiling on the charges incurred during a specified period. For example, in its default
state, a maximum of 830 charge units may be used per week. The router will not permit
the establishment of any further connections once this limit has been reached.
The best way to use the router's call charge monitoring function is if you have “call
charge information enabled
during the connection“ to the ISDN network (i.e. AOCD). If
necessary, subscribe to this facility from your telecommunications carrier. Charge
monitoring with the “Charge information
after connection“ feature is also possible in
principle, but in this case continuous connections may not be detected!