uCertify Articles » CIW Associate Design Specialist http://www.ucertify.com/article Just another WordPress weblog Wed, 04 Nov 2009 00:00:00 +0000 http://wordpress.org/?v=2.8.4 en hourly 1 What is OSPF? http://www.ucertify.com/article/what-is-ospf.html http://www.ucertify.com/article/what-is-ospf.html#comments Sun, 01 Nov 2009 00:00:00 +0000 uCertify 2101094

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 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.

Pass Master CIW Web Site Manager in first attampt. Click here to get free 1D0-520 CIW Site Designer v5 exam practice questions. Share/Bookmark]]> http://www.ucertify.com/article/what-is-a-radial-symmetry-balance-visual-design-2.html/feed 0 Different types of attacks http://www.ucertify.com/article/different-types-of-attacks-2.html http://www.ucertify.com/article/different-types-of-attacks-2.html#comments Sun, 30 Aug 2009 00:00:00 +0000 uCertify 1401665

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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Dynamic HTML (DHTML) is built on an object model that extends the traditional static HTML document. It enables Web authors to create highly interactive Web pages. DHTML provides a set of technologies for creating dynamic content for Web sites. Using DHTML, the content is dynamically rendered and altered on the client without having to make a round trip to the server.

DHTML has the following component technologies:

  • Document Object Model
  • Dynamic Styles
  • Dynamic Positioning
  • Dynamic Content
  • Data Binding

It is important to know about the Document Object Model (DOM). DOM is a road map through which any element in an HTML/XML document can be located. According to the World Wide Web Consortium, the DOM is a platform- and language-neutral interface that allows programs and scripts to dynamically access and update the contents, structure, and style of a document. The document can be further processed, and the results of the processing can be incorporated back into the present page. DOM comprises the components listed below:

  • Objects

  • Properties

  • Events

  • Methods

  • Collections

Here are some important facts about DHTML:

  • DHTML uses the DOM interface to manipulate HTML and XML documents and to provide them the logical structure.

  • DHTML is a combination of scripts, style, and HTML objects that provide Web site interactivity.

  • DHTML can be used as an alternative to server-side technologies such as ASP.

  • A major difference between DHTML and HTML is Web site interactivity. DHTML enhances HTML for Web site interactivity.

  • DHTML is often used to make rollover buttons or drop-down menus on a Web page.

  • DHTML is less commonly used for creating browser-based action games.

There are some disadvantages too of using DHTML. It is difficult to develop and debug Web pages due to varying degrees of support among Web browsers of the technologies involved. Due to the variety of screen sizes available, it becomes a difficult task for developers to fine-tune the page for all browsers and screen-size combinations.

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