Firewall – a technical description
by Albert Schempp (DCS, DCP)
In order to understand today’s quite common internet-technology – with focus on
“firewalls” – it is necessary, to know about the history of the internet. Internet in this
context should be understood as infrastructure (data highway) and information pool
(comparable with a giant library).
In former days it was very expensive, rather complicated and quite user frightening to
obtain information from the “internet”. There were only a few internet access
providers - like Compuserve, which sold their internet access service at high prices
and so there were rather few motivated users.
The appearance of the “www”-technology, the availability of user-friendly web-
browsers like Netscape navigator or Microsoft internet explorer, the declining internet
access costs and the continously growing number of internet access providers lead
to an explosive growth of internet users – making the internet attractive even for
criminals (= hackers, crackers, …).
Because of an uprising “war” between companies and those criminals it was
necessary, to secure the access to and from the internet – after some months of
research, some companies offered “firewalls”.
A firewall (= originally: a wall in a building, which protects building-sections behind
the firewall against fire) is a device, which consists of hard- and software-components
and protects a private (= company’s or home) network against threats from the
internet – therefore the firewall has to be installed between the internet access
provider and the private network by using separate interfaces for each of the
connections, as shown in the graph “Firewall Example”. This position allows the
firewall-software to inspect and control the whole data traffic to and from the internet.
Firewall – a technical description
by Albert Schempp (DCS, DCP)
Firewall-rules are the central protection mechanism and are responsible for filtering
“dangerous” data packets – thus preventing the private network from “publishing”
internal information to the internet and blocking unwished intrusion into the private
network.
The preceeding screenshot shows two firewall-rules:
1. Internet-access for the program “ECP Connect Participant Application” is allowed
(both directions)
2. Internet-access for the program “Interwise PushClient” is allowed (both directions)
Further access-methods are able to
- Internet-access is allowed only in one direction (= IN or OUT)
- Internet-access is blocked – no internet-access is allowed
By proper installing and permanent updating the firewall’s software the firewall
companies guarantee, that only entitled users are able to access the private network.
Modern firewall solutions provide a lot more of functions, such as virus-checking,
spam-filtering, intrusion detection, … Because of today’s matter of fact, that private
networks are usually connected to the internet (= eMail, …) the installation of a
firewall has got a big issue of private network security concepts. Current statistics
say, that an Windows XP system, which has an unprotected, direct connection to the
internet will be “captured” within 10 minutes !!!