IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Organisation Remarks
____________________________________________________________________ .........................................
The illustration shows functional units, some of which can be joined
together to form one unit (see Fig. 2), although this gives rise to additional
security problems. The otherwise secure application gateway can, for
example, be open to attack after it assumes the functions of the external
DNS server if the DNS software contains an error.
Configuration of information servers
Information servers which provide information to external users must be
outside the firewall and be considered in the same way as other servers in the
external network. The management of these should either be local or via
special time-limited accesses from the protected network. The data should be
on write-protected data media.
In the event that some data should only be available for the user of the
network to be protected, it is sensible to use further information servers
in the internal screened sub-net (see Fig. 1). These data are then not
accessible from outside and are protected against internal attacks by the
packet filter.
net to be
protected
internal
DNS server
internal
DNS server
packet filter packet filter
application gateway
____________________________________________________________________ .........................................
IT-Baseline Protection Manual: Oktober 2000
external mail server
&
external DNS server
info server
insecure
network
Figure 2: Screened sub-net with application gateway on a separate router
interface.
The illustration shows functional units, some of which can be joined
together to form one unit. This is shown by the external mail and DNS
server.
Configuration of the mail servers
A mail server within the protected network is used for the management of the
alias data base, which is for the purpose of transforming user addresses to a
unified format, for a POP daemon or as a gateway for the connection to
another mail system (e.g. X.400). All internal mail is sent to this server and
then passed on to the outside via an external mail server.
The external mail server in the external screened sub-net creates the
connection with external computers and accepts the mail from here so that the