Linux Troubleshooting Bible

Firewall TheoryIn the most general sense, firewalls look at incoming data packets, examine their source or destination addresses and ports, and make decisions about those packets based on a set of configured rules. Before you can set up a f...

Firewalls in ActionNo matter how complex the firewall is, in its most simple form, a firewall allows and disallows access to specific services based on host addresses, networks, or other such trigger criteria. The services, ports, and daemo...

Linux Firewall MechanismsMost Linux distributions, including Fedora Core, provide two forms of service access control: TCP wrappers and iptables. I use the term access control and not firewalling because TCP wrappers should really not be re...

TCP Wrappers: Securing Local Services As we explained, TCP wrappers is a good choice for a single-homed/stand-alone server on a secure network where you want to limit host/network access to just a couple of services. Many application serve...

iptables and the Single ServerIf you decide that you need more features, or that TCP wrappers can't handle all the services you want to restrict, iptables is probably the best solution for you. In this section, we show you how to configure ...

iptables and Network FirewallsIn this section, we build on the last section's dive into iptables and use it to introduce dual-homed network firewalls. Entire books have been written on the complexities of this subject, so you'll find enough...

Graphical Firewall ToolsThe vast majority of Linux firewalls are now based on iptables. If you've got the hang of iptables, and know how to "get under the hook" and check them at the command-line level, and now just want to streamline the m...

Troubleshooting iptables No matter how careful you are when you set up firewall rules and tables, it's likely that you'll run into a persistent problem that restarting iptables or rebooting doesn't fix. Here are some of the most frequent f...

Firewall ResourcesFirewalling and system/network security is a huge subject. Table 11-3 shows some of the more useful sites and information that you can use to quickly get up to speed on the various topics in this chapter, as well as keep a...

SummaryAnyone with a machine or network that interacts with the Internet should have a firewall in place. Firewalls block unwanted or unknown traffic while letting legitimate packets gain access to valid services or systems. Under Linux, t...