Firewall
258
8.2
What is a Firewall?
BAT54-Rail/F..
Release
7.54
06/08
This service accepts data received by either one of the two sides and depicts
it to the respective other side. What seems to be at first sight a needless mir-
roring of existing data, is on closer examination the far-reaching concept of
Application Gateways: It never exists a direct connection e.g. between a cli-
ent of the local network and a server of the Internet. The LAN workstations
only see the proxy, the workstations of the Internet likewise. This physical
separation of LAN and WAN, makes it quite difficult for attackers to intrude
into the protected network.
Applied to the porter example, the packet will be left at the gate, the courier
is not allowed to enter the company premises. The porter takes the packet,
will open it after checking address and delivery note and will control also the
content. When the packet has taken these hurdles successfully, then the
company internal courier will bring it himself to the addressee of the compa-
ny. He became proxy of the courier on company premises. The other way
around, all employees, wanting to send a packet, have to inform the porter,
which has to collect the packet at the workstation place and which will hand
over the packet to the ordered courier at the gate.
Note: Functions of Application Gateways are not supported by the BAT,
mainly because of the high hardware demands.
Mail
SMTP
HTTP
FTP
Local network
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