Red Hat ENTERPRISE LINUX 4 - INSTALLATION GUIDE FOR IBM S-390 AND IBM ESERVER ZSERIES Installation Manual page 43

Figure 2.11. Firewall Configuration
Next, you can decide whether to enable a firewall for your Red Hat Enterprise Linux system.
No firewall
No firewall provides complete access to your system and does no security checking.
Security checking is the disabling of access to certain services. This should only be
selected if you are running on a trusted network (not the Internet) or plan to do more firewall
configuration later.
Enable firewall
If you choose Enable firewall, connections are not accepted by your system (other than the
default settings) that are not explicitly defined by you. By default, only connections in
response to outbound requests, such as DNS replies or DHCP requests, are allowed. If
access to services running on this machine is needed, you can choose to allow specific
services through the firewall.
If you are connecting your system to the Internet, this is the safest option to choose.
Next, select which services, if any, should be allowed to pass through the firewall.
Firewall Configuration
33