Fedora Linux

the checkboxes for the desired services. SSH should remain selected to permit secure remote administration.

To permit connections to services that are not listed, click on the triangle for 'Other ports.' The display will change to reveal an additional section, as shown in Figure 8-2 .

Figure 8-2. Configuring other ports

To add additional ports, click the Add button, and the window shown on the right side of Figure 8-2 will pop up. Enter the port number or the service name, select TCP or UDP for the protocol, and click OK.  

A list of most of the common services and their corresponding port numbers can be found in the file /etc/services.

When the firewall is configured to your liking, click OK.

8.1.1.1. Configuring the firewall in text mode

Enter this command:

# lokkit

The screen displayed in Figure 8-3 will appear. Use the Tab key to navigate among fields, the spacebar to select and deselect checkboxes, and Enter or the spacebar to activate buttons.

Figure 8-3. Lokkit firewall configuration screen

Enable or disable the firewall using the checkboxes. To customize the types of connections that are permitted through the firewall, tab to the Customize button and press Enter. The customization screen shown in Figure 8-4 will appear.

Figure 8-4. Lokkit firewall customization screen

The Trusted Devices and MASQUERADE Devices checkboxes are applicable only to systems with multiple network connections. Do not select either of those options on a system with a single network interface.

The Trusted Devices checkbox will disable firewall protection for the selected interface! 

Use the Allow Incoming checkboxes to select the services that will be permitted to connect to your system through the firewall. In almost all cases, SSH should be selected to permit secure remote connections for system administration.

To allow incoming connections to services that are not listed, enter the port number or service, followed by a colon (:), and the protocol (TCP or UDP) into the 'Other ports' field at the bottom of the screen. You will need to separate multiple entries with a space or comma. For example, to permit incoming connections to the VNC service as well as to a custom UDP service running on port 64447, use:

vnc:tcp 64447:udp

Select OK to return to the main screen ( Figure 8-3 ); select OK on that screen to save your settings and exit.

8.1.1.2. Temporarily disabling the firewall from the command line

To disable the firewall until the next reboot, stop the iptables service:

# service iptables stop

To reset your firewall to the configured settings, restart the iptables service:

# service iptables restart

8.1.2. How Does It Work?

The Fedora firewall uses the kernel's iptables capability, which can filter packets based on their source, destination, port, protocol, contents, and current connection state.

To view the current iptables configuration, use the -L option:

# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
RH-Firewall-1-INPUT all -- anywhere anywhere
Chain FORWARD (policy ACCEPT)
target prot opt source destination
RH-Firewall-1-INPUT all -- anywhere anywhere
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain RH-Firewall-1-INPUT (2 references)
target prot opt source destination
ACCEPT all -- anywhere anywhere
ACCEPT icmp -- anywhere anywhere icmp any
ACCEPT ipv6-crypt-- anywhere anywhere
ACCEPT ipv6-auth-- anywhere anywhere
ACCEPT udp -- anywhere 224.0.0.251 udp dpt:mdns
ACCEPT udp -- anywhere anywhere udp dpt:ipp
ACCEPT tcp -- anywhere anywhere tcp dpt:ipp
ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED
ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:ssh
REJECT all -- anywhere anywhere reject-with icmp-host-prohibited

There are four chains of rules defined here:

INPUT

Filters packets that are inbound to this system.

FORWARD

Filters packets that are passing through the system. This applies only if there is more than one network