Open Shortest Path First (OSPF) is a routing protocol that is used in large networks. Internet Engineering Task Force (IETF) designates OSPF as one of the Interior Gateway Protocols. A host uses OSPF to obtain a change in the routing table and to immediately multicast updated information to all the other hosts in the network.

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The AutoFill feature of a browser automatically fills the text in the text box as the user types. It does not suggest any options as done by the AutoComplete feature. The AutoFill feature can be set by the user of the browser and not by the author of the Web site.

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The Internet is used by millions of people worldwide. It provides many online facilities, which are as follows:

• E-mail
• Chat
• E-commerce
• E-banking
• Search engines

The Internet provides all these facilities through Web sites, which are loaded on different Web servers. A Web site is a collection of one or more Web pages that are created using Hypertext Markup Language in combination with different languages such as ASP, Java, VBScript, and JavaScript, etc. These languages are used to connect a Web page to a database, to create client/server applications, etc.

Hypertext Markup Language or HTML is a language that is used to create Web pages. These Web pages are linked together with one another to create a Web site. Every Web page in a Web site has its own URL.

Using different HTML tags can create a Web page. Some of the HTML tags are as follows:

Linking tags:

The <a> tag: The <a> tag is used to create a hyperlink. Hyperlink is a text that is used to link the Web pages of a Web site with one another or to the Web pages of another Web site. A hyperlink can be created using the <a> tag. The following example will demonstrate the use of the <a> tag:

<a href=”mypage.html”>My page</a>

The <map> and <area> tags:

Image maps can be used to connect Web pages of a Web site with one another or to the Web pages of another Web site. An image map is used to divide an image into multiple sections. Each section of the image can be linked to an HTML document. The image maps can be created using the <map> and <area> tags. The following example will demonstrate the use of an image map:

<map name=”mymap”>
<area shape=”rect” coords=”60 80 100 40″ href=”page1.html”>
<area shape=”rect” coords=”120 80 100 40″ href=”page2.html”>
</map>

<img src=”myimg.gif” usemap=”#mymap”>

The formatting tags:

The <b> tag: The <b> tag is a formatting tag that is used to display text in bold.

The <bdo> tag: The <bdo> tag is used to reverse text.

The <big> tag: The <big> tag is used to display text larger than its normal font size of text in a Web page.

The <center> tag: The <center> tag is used to insert text horizontally in the center of a line.

The <cite> tag: The <cite> tag is used to display text in italics.

The <code> tag: The <code> tag is used to write text that is preformatted.

The <del> tag: The <del> tag is used to define text that has been delayed in a document.

The <dfn> tag: The <dfn> tag is used to define a definition term.

The <em> tag: The <em> tag is used to emphasize a particular text.

The <font> tag: The <font> tag is used to define the font face, font size, and font color of a text.

The heading tags:

There are six heading tags in HTML, which are used to provide headings for the topics and subtopics in a document. The heading tags start from <h1> to <h6>. Each of these has different font sizes. The font size of the <h1 > is the largest and it decreases from <h1> to <h6>.

The <i> tag: The <i> tag is used to display text in italics.

The <ins> tag: The <ins> tag is used to define an inserted text in a document.

The <kbd> tag: The <kbd> tag is used to display the keyboard text.

The <p> tag: The <p> tag is used to define a paragraph.

The <pre> tag: The <pre> tag is used to define a pre-formatted text. The text enclosed in this tag preserves the line breaks and spaces.

The <s> and <strike> tags: The <s> and <strike> tags are used to strike out text.

The <small> tag: The <small> tag is used to display text that is smaller than the normal font size of the text in a Web page.

The <strong> tag: The <strong> tag is used to emphasize a text strongly.

The <sub> tag: The <sub> tag is used to display a subscript text.

The <sup> tag: The <sup> tag is used to display the superscript tag.

The <tt> tag: The <tt> tag is used to display a teletype or monospaced text.

The <u> tag: The <u> tag is used to underline a text.

The following example will demonstrate the use of the formatting tags:

<b>This is a bold text.</b>
<bdo dir=”rtl”>This is a text</bdo>
<big>This is a big text.</big>
<center>This text will be in center</center>
<cite>This is a cite</cite>
<code>This is a code.</code>
<del>This is a deleted text</del>
<dfn>This is a definition term</dfn>
<em>This is an emphasized text.</em>
<font face=”verdana” size=”4″ color=”green”>This is a font text.</font>
<h1>heading 1</h1>
<h2>heading 2</h2>
<h3>heading 3</h3>
<h4>heading 4</h4>
<h5>heading 5</h5>
<h6>heading 6</h6>
<i>This is the text in italics.</i>
<p>This is <ins>inserted</ins> text.
<kbd>This is a keyboard text</kbd>
<p>This is first paragraph.
<p>This is second paragraph.
<pre>This is a preformatted text.</pre>
<s>This is an strike out text.</s>
<strike>This is an strike out text.</strike>
<small>This is a small text.</small>
<strong>This is a strong emphasized text</strong>
<p>The chemical formula of water is H₂O.
<p>James will leave on 27^th December.
<tt>This is a teletype text</tt>
<u>This is an underlined text</u>

The output is as follows:

This is a bold text.
This is a text
This is a big text.

heading 1

heading 2

heading 3

heading 4

heading 5

heading 6

This is the text in italics.

This is inserted text.

This is a keyboard text

This is first paragraph.

This is second paragraph.

This is a preformatted      text.

This is an strike out text.
This is an strike out text.
This is a small text.
This is a strong emphasized text

The chemical formula of water is H₂O

James will leave on 27^th December.

This is a teletype text
This is an underlined text

The container tags:

The <body> tag: The <body> tag is used to create the document of an HTML page. Most of the tags are used inside the <body> tag.

The <frameset> and <frame> tags: The frameset and frame tags are used to divide a window in two or more sections. Each frame in a frameset can contain a separate HTML document. The <frameset> tag is the container of all the frames. These tags cannot be used within the <body> or <head> tags. The following example will demonstrate the use of the <frameset> and <frame> tags:

<frameset cols=”50%,50%”>
<frame src=”page1.html”>
<frame src=”page1.html”>
</frameset>

This code will divide a browser window vertically in two sections.

The <head> tag: The <head> tag contains the information about an HTML document such as title. The code of other languages such as JavaScript, VBScript, etc. can be used within the <head> tag. The <head> tag is inserted just after the <html> tag. The following example will demonstrate the use of the <head> tag:

<head>
<title>Title</title>
</head>

The title given in the <title> tag will be shown on the title bar of a browser window.

The <html> tag: The <html> tag is the first tag of an HTML document. All the other tags are contained within this tag.

The <iframe> tag: The <iframe> tag is used to create an inline frame. The inline frame can contain another document. The following example will demonstrate the use of the <iframe> tag:

<iframe src=”page1.html”></iframe>

Miscellaneous tags:

The <br> tag: The <br> tag is used to insert a single line break between two statements or two paragraphs.

The <hr> tag: The <hr> tag is used to draw a horizontal line in a document.

The <img> tag: The <img> tag is used to insert images in an HTML document. The format of the image should be GIF or JPEG.

The following example will demonstrate the use of the miscellaneous tag:

This is first line.<br>This is second line
<p>This is a text.
<hr>
<p>This is a text.
<img src=”img1.gif”>

The output is as follows:

This is first line.

This is second line

This is a text.

This is a text.

The <meta> tag: The <meta> tag is used to convey hidden information about a document, such as keywords, description, etc., to the server and the client. It also embeds the document information that is used by some search engines to index and categorize documents on the World Wide Web. <meta> tags can be used only within the head section of a Web page. It does not require a closing tag.

The <table> and its elements:

The <caption> tag: The <caption> tag is used to give a caption inside a table. The <caption> should be inserted just after the <table> tag.

The <col> tag: The <col> tag is used for inserting columns in the <table> tag.

The <colgroup> tag: The <colgroup> tag is used within the <table> tag to format a group of columns in a table.

The <table> tag: The <table> tag is used to display the data in tabular form.

The <td> tag: The <td> tag is used to define a cell in a table.

The <th> tag: The <th> tag is used to define a heading in a table.

The <tr> tag: The <tr> tag is used to define a row in a table.

The following example will demonstrate the use of all the tags in a <table > tag:

<table border=”1″><caption>This is a caption</caption>
<colgroup span=”3″>
<col width=”50″></col>
<col width=”50″></col>
<col width=”50″></col>
</colgroup>
<tr>
<th>Heading 1</th>
<th>Heading 2</th>
<th>Heading 3</th>
</tr>
<tr>
<td>First column</td>
<td>Second column</td>
<td>Third column</td>
</tr>
</table>

The output is as follows:

The <form> tag and its elements:

The <fieldset> tag: The <fieldset> tag is used to draw a box around the form elements.
The <form> tag: The form tag is used to create the form for user input. The form itself is not visible, but the form elements such as textfields, drop-down menu, checkboxes etc. are visible.

The <input> tag: The input tag is used within the form tag to create the form elements for user input.

The <label> tag: The <label> tag is used to toggle a form element such as checkbox or the radio button.

The <legend> tag: The <legend> tag is used to define a caption for a fieldset.

The <optgroup> tag: The <optgroup> tag can be used for creating a group of elements in a drop-down list.

The <option> tag: The <option> tag is used to add options in a drop-down list.

The <select> tag: The select tag is used to create a drop-down list on a Web page.

The <textarea> tag: The <textarea> tag is used to create a multiple line text field on a Web page.

The <button> tag: The <button> tag is used to create the button object. The button can be a push button, submit button, or reset button.

The following example will demonstrate the use of the <form> tag and its elements:

<form><fieldset><legend>User data</legend><input type=”text”>
<input type=”text”><input type=”checkbox” id=”c1″><label for=”c1″>Check 1</label><input type=”checkbox” id=”c2″><label for=”c2″>Check 2</label>
<select><optgroup label=”Alphabets”></optgroup><option>A</option>
<option>B</option><option>C</option><optgroup label=”Numbers”></optgroup><option>1</option><option>2</option>
<option>3</option></select><textarea rows=”5″ cols=”5″></textarea>
<button>Click me</button> </fieldset></form>

The output is as follows:

The list tags:

The <li> tag: The <li> tag is used to define a list items. It can be used with the <ul> and <ol> tags. The following will demonstrate the use of the <li> tag:

<ul>
<li>item 1</li>
<li>item 2</li>
</ul>

The output is as follows:

• item 1
• item 2

<ol>
<li>item 1</li>
<li>item 2</li>
</ol>

The output is as follows:

1. item 1
2. item 2

The fourth normal form states that the database must be in BCNF and all the multivalued dependencies in the table are also functional dependencies whose determinant is a candidate key. Symbolically, if A -> > B|C, then A -> B and A -> C. Here, A, B, and C are attributes.

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The 1NF is a normalization form in which each column in a row contains a single value, i.e., each attribute of the entity is single valued. Single valued attributes are also known as atomic attributes, as they cannot be decomposed into smaller units. There are mainly three kinds of attributes that prevent a table from being in the first normal form. They are as follows:

• Composite attributes
• Plural attributes (attributes that have more than one value)
• Attributes with complex data types

The table below is in 1 NF, as all the columns in each row contain a single value.

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Network Load Balancing is a Windows Server 2003 clustering technology. It runs as a driver in Microsoft Windows and distributes incoming requests across each node included in the cluster. Its primary purpose is to load-balance by distributing TCP/IP traffic among the server nodes in a cluster. For load balancing-aware applications, such as Exchange Server 2003, when one of the nodes fails or becomes offline, the load is automatically distributed to other nodes in the cluster. A cluster using Network Load Balancing can have 2 to 32 nodes. Administrators can configure it through the Network Load Balancing Manager, which is located in the Administrative Tools program menu.

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IP masquerading is a form of network address translation that is generally employed by firewalls and routers. Through this method, a Linux computer with a valid IP address can act as a gateway for other computers in the LAN, which do not have a valid IP address. The computers without a valid IP address can then access the Internet through this gateway. The computers on the LAN, having no valid IP address can use their private addresses to connect to the configured gateway. When the gateway receives a packet from such a computer, it assigns it a new source port number and inserts its own IP address into the header of the packet. This packet is then sent to the Internet as if it came from the gateway. When the gateway receives an incoming packet, it searches if the port number is one of those that it assigned previously to such a computer. If a match occurs, the gateway retrieves the original port number and private IP address of the corresponding computer and inserts them into the packet header. This packet is then sent to the destined computer.

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Inline scripting is a method of scripting in which the script is embedded within the HTML tags of a Web page. It provides control to a Web page when events, such as button click, text entry, form submission etc., occur. Inline scripting is also used to provide information to a Web page from the Web server.

The following is an example of an inline script, for the onfocus and onblur events, embedded in an HTML tag :

<INPUT name=”NAME” onblur=”this.style.backgroundColor=’#ffffff’” onfocus=”this.style.backgroundColor=’#ffff00′”>

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A radial symmetry balance visual design is a type of symmetrical design. This type of design occurs when elements are equally spaced around a central point.

In computer systems and networks, security is concerned with privacy, integrity, and protection from unauthorized access, modification, and deletion. It is an effort that needs proper planning, implementation, and maintenance to ensure that the user’s data remains secure. The first step to create a secure Internet platform is to find out the expected attacks and then take the necessary steps to protect your computer or network against such attacks.

Attack

An attack is the act of trying to bypass security controls on a computer system. It can be active or passive. An active attack is an attack in which the attacker manipulates data and adds unauthorized data. In a passive attack, the attacker only monitors and/or records data.

To secure a network from attacks, it is necessary to detect when and what type of attack is taking place. Some of the common attacks are listed bellow:

Password guessing attack

This attack occurs when an unauthorized user repeatedly tries to log on to a computer or network by guessing usernames and passwords. Many password-guessing programs that attempt to break passwords are available on the Internet. Following are the types of password guessing attacks:

• Brute force attack: Brute force attack is a type of password guessing attack. In this type of attack, attackers systematically try every conceivable combination to find out the password of a user.
• Dictionary attack: Dictionary attack is a type of password guessing attack. This type of attack uses a dictionary of common words to find out the password of a user. It can also use common words in either upper or lower case to find a password. There are many programs available on the Internet to automate and execute dictionary attacks.

DoS attack

A Denial-of-Service (DoS) attack causes a negative impact on the performance of a computer or network. This attack is designed to bring loss of network connectivity and services by consuming the bandwidth of the user’s network. It is also known as network saturation attack or bandwidth consumption attack. Attackers make Denial-of-Service attacks by sending a large number of protocol packets to a network. A DoS attack can cause the following:

• Saturate network resources.
• Disrupt connections between two computers, thereby preventing communication between services.
• Disrupt services to a specific computer.

A Denial-of-Service attack is very common on the Internet because it is much easier to accomplish. Most of the DoS attacks rely on the weaknesses in the TCP/IP protocol. Some of the common DoS attacks are as follows:

• SYN attack: A SYN attack is a common denial-of-service (DoS) technique. Using this technique, an attacker sends multiple SYN packets to the target computer. For each SYN packet received, the target computer allocates resources and sends an acknowledgement (SYN-ACK) to the source IP address. Since the target computer does not receive a response from the attacking computer, it attempts to resend the SYN-ACK. This leaves TCP ports in a half-open state. When an attacker sends TCP SYNs repeatedly, the target computer eventually runs out of resources and is unable to handle any more connections, thereby denying services to legitimate users.

  A SYN attack affects computers running on the TCP/IP protocol. It is a protocol-level attack that can render a computer’s network services unavailable. A SYN attack is also known as SYN flooding.

• PING attack: A PING attack is a denial-of-service technique. In this technique, a computer repeatedly sends illegitimate, oversized ICMP echo requests to another computer. PING attacks are targeted to specific TCP stacks that cannot handle ICMP packets. These attacks overload the targeted servers with fake packets.
• Flood attack: In this attack, an attacker sends more and more traffic to the victim than it could handle. It is the simplest denial attack but most difficult to completely prevent.
• Teardrop attack: In a Teardrop attack, corrupt packets are sent to the victim’s computer by using IP’s packet fragmentation algorithm. As a result of this attack, the victim’s computer might hang.
• Smurf attack: In this attack, an attacker sends a large number of ICMP echo requests at IP broadcast addresses using a fake source address. These requests appear to be coming from the victim’s network address. Therefore, every computer within the broadcast domain starts sending responses to the victim. As a result, the victim’s computer is flooded with responses.

Vulnerability attack

A vulnerability attack takes advantage of the vulnerabilities in an operating system or software service by entering the operating system and disrupting its working.

Impersonation attack

An impersonation attack attempts to access the computer by using a valid user password.

Replay attack

Replay attack is a type of attack in which attackers capture packets containing passwords or digital signatures whenever packets pass between two hosts on a network. These attackers then filter the data and extract the passwords, encryption keys, or digital signatures from the captured packets. In an attempt to obtain an authenticated connection, the attackers then resend this information to the system.

Man-in-the-middle attack

Man-in-the-middle attacks occur when an attacker successfully inserts an intermediary software or program between two communicating hosts. The intermediary software or program allows attackers to listen to and modify the communication packets passing between the two hosts. The software intercepts the communication packets and then sends the information to the receiving host. The receiving host responds to the software, presuming it to be the legitimate client.

Spoofing

Spoofing is a technique that makes a transmission appear to have come from an authentic source by forging the IP address. In IP spoofing, a hacker modifies packet headers by using someone else’s IP address to hide his identity. However, spoofing cannot be used while surfing the Internet, chatting on-line, etc., because forging the source IP address causes the responses to be misdirected.

Back Door

Back door is a program or account that allows access to a system by skipping the security checks. Many vendors and developers implement back doors to save time and effort by skipping the security checks while troubleshooting. Back door is considered to be a security threat and should be kept with the highest security. If a back door becomes known to attackers and malicious users, they can use it to exploit the system.

Hacking

Hacking is a process by which a person acquires illegal access to a computer or network through a security break or by implanting a virus on the computer or network.

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