netfilter Operation: Part Twelve (Firewall Builder continued)

Firewall Builder

Firewall Builder on startup.

NOTE: After I posted this article, I found out it’s possible to add objects/networks/hosts/etc. by right-clicking items on the object tree under the Linux version of Firewall Builder. This article has been amended accordingly.

In the previous article, I introduced Firewall Builder, including some notes on installation under Windows and Linux. In this article, I will step through the process of adding a firewall object and configuring it.

Firewall Builder: Creating a Firewall Object

In this example, I installed Firewall Builder under Linux Mint. Initially, there are three main options in the main dialog area: “Create New Firewall“, “Import Existing Configuration“, and “Watch ‘Getting Started’ Tutorial“. click on “Create New Firewall“, which will open the New Firewall dialog box.

Firewall Builder

The New Firewall dialog box.

In the New Firewall dialog box, enter the name for the new firewall (in this case OFFICE01). For the firewall software, select iptables from the dropdown box. For the OS, choose Linux 2.4/2.6 and click Next. The next window allows you to configure the interfaces on the firewall. You can do it manually, or if the firewall is running SNMP, you can discover them via SNMP. Here, we select Configure interfaces manually and click Next. This will bring up the manual configuration window. Enter the relevant information for each network interface. The name must correspond to the actual interface name (which is the same as if you had entered ifconfig on the Linux host), such as eth0. The Label is a human friendly name for easy reference such as OUTSIDE. When you are done entering the information for a given interface click Add. When you have entered the information for all interfaces (typically at least an INSIDE and OUTSIDE), click Finish. You must designate one of the interfaces on the firewall as the management interface, typically the INSIDE interface. Do this by navigating to the firewall in the object tree. As you select each interface in the object tree, there is a “Management interface” checkbox in the dialog area. Check this box for the interface you want to use. This will be the interface that Firewall Builder uses to connect and upload the firewall rules to.


Firewall Builder: Adding a Network

Firewall Builder

The button for adding new networks/hosts/services/etc is in the upper left, adjacent to the back arrow button.

Now that you have the basic firewall defined, you need to define something for it to talk to. In this case, we will assume that 192.168.1.0/24 is you internal network, and you want to allow outbound Web browsing and access to an internal Web server (WEB1). For starters, you need to create an object to represent the internal network. Follow these steps to create the network object:

  1. Navigate to Objects -> Networks in the object tree ((in order to make the object tree visible, you may have to go to the View menu and unselect Editor Panel).
  2. Right-click Networks and select New Network.
  3. Enter INTERNAL for the name of the network, and use 192.168.1.0 for the Address field. Enter 255.255.255.0 for the Netmask.
  4. Next, we’ll create an internal Web server at 192.168.1.2.  Right-click Objects -> Hosts in the object tree and select New Host.
  5. Enter WEB1 for the name of the object. Click the Use preconfigured template host objects check box and click Next.
  6. Select PC with one interface and click Finish.
  7. Expand the object tree to User -> Objects -> Hosts -> WEB1 -> eth0 -> WEB1. Edit the IP address to be 192.168.1.2 and click Apply.
  8. Next, define the appropriate services to allow Web-browsing. Navigate in the object tree to Services -> TCP, right-click on it, and select New Service.
  9. Enter HTTP for the name. Leave the source port ranges at zero, but change the destination port range to start and end at 80.
  10. Repeat the previous two steps for HTTPS on port 443 for secure Web pages.

Now that we have created the network object, in the next article, we will cover defining the firewall rules to allow inbound web traffic and uploading the rules to the firewall.


External Links:

The official Firewall Builder web site

Using Firewall Builder on Linux to Create Firewalls from Scratch on linux.com

Firewall Builder Tutorial: The Basics on YouTube

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