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Network Configuration and Security / iptables Firewall Rules
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Subtitles of the Movie (Red Hat Certified Engineer / Network Configuration and Security / iptables Firewall Rules)
We continue our series of videos on iptables with tips on how you can configure a Firewall. While it's generally best and fastest to do everything from the command line, I recognize that Firewall rules are one of the more difficult skills for the Linux administrator, and it's okay to use all available tools. It doesn't matter how you solve a problem during the RHCE exam, or in real life, as long as you don't cheat. So, let's take a look at the security level configuration tool. It's available in the GUI, or in Text Mode, using the appropriate command. I've opened the GUI version of the security level configuration tool with the system config security level command. It's available in Text Mode, too. Now, let's look at the GUI version of the tool. The first thing you can do is enable, or disable the Firewall. If you disable the Firewall it deletes etc slash sysconfig slash iptables. Let's not do that right now. In fact, let's make a copy of it. It's a good practice in case something goes wrong. Note the variety of service options available in the trusted services box. These are common services. If you want to make them available to outside networks you want to make them trusted services with access through your Firewall. These are straightforward and open certain ports. Some, like FTP, open single ports, in this case, port 21. Mail opens port 25, and so on. These are defined in the etc slash services configuration file. Others, such as Samba, open multiple ports. Let's take a quick look at the current version of etc slash sysconfig slash iptables. For the purpose of this video I add secure www, associated with the secure HTTP protocol to the Firewall, and click OK, and I override the existing Firewall configuration. What happens? I see a new Firewall rule associated with port 443. And if you have the experience to be an RHCE, you should already recognize port 443 as associated with secure HTTP, but you can always look it up in the etc slash services configuration file. Remember there are 65,000 ports available for tcp ip. You may want to unblock some other port, and that's possible. Just click the Other Port's arrow. This opens a port's window and you may want to work with the port, say, what was the port for the imap server? We look it up in the etc slash services configuration file, and see that it's associated with port 143 using both the tcp and udp protocols. So we add port 143 as a trusted service, using both the tcp and udp protocols. Save the result, override the existing Firewall configuration and look at that. I have a couple more Firewall rules, opening up port 143 for tcp and udp communication; that shouldn't surprise you. We open up the security level configuration tool again and look at that. It actually refers to etc slash services to name the port. As an exercise on your own time, listen to this video again. Try to do the same things with the console-based security level tool, which you can start with the system config security level dash tui command. The console-based tool actually supports making a NETwork card into a trusted device as well as specifying the network card, it's used to Masquerade the ip address on a local network. There is a lot to learn with Firewalls, so I leave this task up to you. Don't forget to check the effective changes on the etc slash sysconfig slash iptables configuration file.
Tutorial Information
| Course: | Red Hat Certified Engineer |
| Author: | Michael Jang |
| SKU: | 33845 |
| ISBN: | 1-934743-47-X |
| Release Date: | 2008-01-18 |
| Duration: | 6.5 hrs / 94 lessons |
| Captions: | No |
| Compatibility: |
Vista/XP/2000, OS X, Linux QuickTime 7, Flash 8 |
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