Firewalls in Ubuntu -- details and configuration

Ubuntu Linux has mainly two strong firewalls, namely:

1. Netfilter
2. Firestarter

Netfilter firewall:

Ubuntu has a powerful firewall called netfilter that is part of the central kernel program. The ufw command at the terminal allows us to configure the firewall. However, this command needs you to be root of the system. For this purpose, we add sudo in before the command. For example, to enable the netfilter firewall we type the command as: sudo ufw enable. The manual pages for this firewall can be seen by typing the command: man ufw. 

However, this firewall can be operated in a more user-friendly way, by installing the package named Firewall Configuration. This package supports common tasks such as allowing or blocking pre-configured, common p2p, or individual ports, and many others. Rules can be easily added, removed and edited with the help of this interface. The interface is simple with easy usage and is recommended for beginner users.

We can configure the netfilter firewall by --

1. Adding allow, deny and limit rules.
2. Enabling, disabling and reloading the firewall.
3. Deleting and Inserting rules.
4. Displaying the information and status of the firewall.

Firestarter firewall:

Another user-friendly Firewall in Ubuntu is Firestarter. On the start-up for the first time, a wizard will be run, for configuring the network states. You can read the manual pages of this firewall by the command: man firestarter. There are three pages/tabs in the Firestarter interface, namely --

1. Status page giving an overview of the firewall state. 
2. Events page, where blocked intrusion attempts and the firewall history is shown.
3. Policy page for altering the behaviour of the firewall.

This firewall can be in one of these three states: Active, Disabled and Locked (Nothing is allowed through the firewall, neither in nor out). The Network section of the status page gives an overview of the network resource usage. In addition, the status page also lists the Active connections, the firewall is tracking every moment. The entries in the Active connections are color coded as: Gray for a terminated connection and black for a currently active connection. However, terminated connections are removed from the list after 10 seconds.

The Events page shows the history of connections blocked by the firewall. The entries in the Events page can be allowed connections from source, port or everyone or can be disabled events from source or port. The Firestarter colour codes the entries as:

1. Black -- A regular connection.
2. Red -- A possible attempt to access a non-public service and needs special attention.
3. Gray -- Harmless connections, mostly broadcast.

The third page, Policy can add, edit or remove rules for the firewall. Two types of rules can be created: Inbound rules, that allow through connections from the network or Internet, and Outbound rules, that can block unauthorised data emissions from your computer, such as those from potential virus infections, or spyware. Inbound rules allow you to filter all incoming connections. When it comes to blocking data emanating from your computer, Firestarter can enact two different modes:

1. Whitelist: In this mode, network traffic is not allowed out of the computer unless a rule allows it. This is also known as restrictive policy. 
2. Blacklist: In this mode, which is default, all traffic is allowed out of the computer unless a rule specifically forbids it. This is also known as permission policy.

Java Swing applications -- Telephone and Address Book -- II

Implementation:

The Telephone Book application is now designed and we need to just put the coding for that. We already know which objects in swing package are used as the components in the panels for the application. For example, we have mentioned in the last post about some components such as Drop-down list (JComboBox), Labels for the appropriate components(JLabel), Buttons (JButton), Text-Boxes (JTextBox), Scroll Panes (JScrollPane), Results displayed in Tables (JTable), Confirmation of the results through Dialogs (JDialog) etc.

The Front end is Java Swing while the application has a database connectivity with MS Access database. As mentioned in the previous post, there is only one table in the database. The coding is done in two packages: 

1. TeleAddress package for Component design and Action listeners &
2. dao package for accessing database from the MS Access database through JDBC API

In all the classes, the constructors play a key role with initializing the frame window processing purposes. Mouse action listeners are applied to the buttons in the interface that interacts with the user, most of them being applied when the user clicks the mouse.

The confirmation dialogs are present in a separate class, named Dialogs with separate dialogs for contact creation, updating contacts and contact-deletion. The Dialogs class contains the following:

1. Two Constructors -- one for Deletion and the other for Updation / Addition of contacts
2. dialog( ) and deldialog( ) functions for processing one of the two constructors.

The TelephoneBook class in TeleAddress package is the main class in the application and binds all the classes together. The TelephoneBook class contains the following:

1. All the Interface-Components such as Buttons, Drop-down lists, Text-Boxes,Labels,Tables etc. are defined in this class.
2. 5 Panel functions for adding the components into each panel.
3. A Constructor having function calls to the Action-listeners.
4. A function named initComponents( ) for the lay-out of components.
5. All Action-listeners for all the buttons such as Create, Delete, Update, Refresh, Cancel etc.

The SearchTable class allows the user to view the results in a table in a different Frame window. The Database class consists of all the database-connections, where we use the JDBC-ODBC Bridge Driver for connecting to MS Access. The static methods in this class are used for every database operation being done in the application. The dao package makes use of PreparedStatement and Statement for database query executions. The Database connectivity with MS Access can be done as shown clearly in these posts as part 1, part 2 and part 3. The dao package has the data access objects listed below:

1. Database class for Database connection.
2. AddDAO class for insertion of new contact into the database table.
3. DeleteDAO class for deletion of contact records from the database table.
4. OtherDAO class to get all the records from the database table
5. SearchDAO class to facilitate searching upon inputs given in the Search and Delete panels.
6. UpdateDAO class for updating contact details.

The documentation for the classes of this application have been automatically generated by NetBeans IDE through Javadocs which can be downloaded here.

Installation and Configuring the application:

Pre-requisites:

1. The system should have Java (JDK and JRE) installed on your system, which can be downloaded from this page.
2. The system should have Microsoft Office Access DBMS.

Configuring and Installation:

1. Invoke Control Panel -- Administrative Tools -- Data Sources (ODBC). Go to UserDSN tab and click on Add button.
2. Select Microsoft Access Driver (*.mdb, *.accdb) and click on Finish button.
3. Give the Data Source Name as TeleAddressBook and select the Database Select button and give the path of the database file which can be downloaded from here. After selecting the .accdb file, click OK. Any doubts regarding the configuration of DSN (Data Source Name) can be clarified with the tutorial specified previously at this post with screen-shots.
4. Download the JAR file which can be downloaded here.
5. After configuring the DSN and downloading the JAR file, double-click on the JAR file to invoke the application. If its not invoked with the double-click then open Command-Prompt and type the one specified as: java -jar "/* Complete Path of the JAR file */"