Specifications

Protocol icmp ftp ssh smtp http https . . .

Client internal external i. e. i. e. i. e. i. e. i. e.

host1 x – x – – – x – x – –

host2 x – – – x – x – – – – –

host3

. . .

hostn

With the help of such a communication matrix, obtain an overview of the com-

munication constellations within the network. This simpliﬁes the conﬁguration

of your network and error analysis.

Typical Firewall Setups

This section gives a brief overview of the most typical ﬁrewall setups. All the

conﬁgurations presented below can be implemented with the SuSE Firewall on

CD.

Figure 1.1: Very Basic Setup

Figure 1.1 shows a ﬁrewall with three network interfaces: an external one to

connect to the Internet and two internal ones connecting with the corporate

network via LAN or HUB and with the DMZ (demilitarized zone) using another

HUB. With this setup, the ﬁrewall has to perform all the functions of the default

gateway (router) and the packet ﬁlter. The internal network would be left

completely open if the ﬁrewall were inﬁltrated.

The setup shown in Figure

1.2 on the facing page is still a relatively simple one.

The DMZ is only protected by a packet ﬁlter on the router (screening router).

The setup shown in Figure 1.3 on the next page is still not very complicated, but

provides much better protection than the previous ones. A “screening router”

12 Typical Firewall Setups