Ways of securing computer networks

• Access authorization restricts access to a computer to group of users through the use of authentication systems. These systems can protect either the whole computer - such as through an interactive logon screen - or individual services, such as an FTP server. There are many methods for identifying and authenticating users, such as passwords, identification cards, and, more recently, smart cards and biometric systems.

• Anti-virus software consists of computer programs that attempt to identify, thwart and eliminate computer viruses and other malicious software (malware).
• Application with known security flaws should not be run. Either leave it turned off until it can be patched or otherwise fixed, or delete it and replace it with some other application. Publicly known flaws are the main entry used by worms to automatically break into a system and then spread to other systems connected to it.
• Backups are a way of securing information; they are another copy of all the important computer files kept in another location. These files are kept on hard disks, CD-Rs, CD-RWs, and tapes. There is also a fourth option, which involves using one of the file hosting services that backs up files over the Internet for both business and individuals.
• Encryption is used to protect the message from the eyes of others. It can be done in several ways by switching the characters around, replacing characters with others, and even removing characters from the message. These have to be used in combination to make the encryption secure enough, that is to say, sufficiently difficult to crack.
• Firewalls are systems which help protect computers and computer networks from attack and subsequent intrusion by restricting the network traffic which can pass through them, based on a set of system administrator defined rules.

• Honey pots are computers that are either intentionally or unintentionally left vulnerable to attack by crackers. They can be used to catch crackers or fix vulnerabilities.
• Intrusion-detection systems can scan a network for people that are on the network but who should not be there or are doing things that they should not be doing, for example trying a lot of passwords to gain access to the network.
• Pinging:The ping application can be used by potential crackers to find if an IP address is reachable. If a cracker finds a computer they can try a port scan to detect and attack services on that computer.
• Social engineering awareness keeps employees aware of the dangers of social engineering and/or having a policy in place to prevent social engineering can reduce successful breaches of the network and servers.

Computer Network Notes

Computer Network

In connection with the information technology and computers a network is a way to connect computers together so that they can communicate, exchange information and pool resources or a network is a communicating system connecting two or more computers. Network connects people as close as the next office and as for as halfway around the world.

In business networks have revolutionized the use of computer technology. Many businesses that used to relay on a centralized system with mainframe and a collection of terminals now use computer networks in which every employee who needs a computer has personal computer connected to the network. In education, schools, colleges and universities have also shifted to strategies built around networked personal computers.

Configurations or Topologies Networks

A network can be arranged or configured in several different ways. This arrangements is called the network's topology. The four principal network topologies are

1. Star Network

2. Bus Network

3. Ring Network

4. Hierarchical Network

1. Star Network

In a star network small computers or peripheral devices are linked to a central unit. This central unit may be a host computer or a file server. All the communications pass through this central unit. Control is maintained by polling. Each device is in turn allowed to send the message.

One particular advantage of the star form of network is that it can be used to provide a time-sharing system. i.e several users can share resources (time) on a central computer. The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organizations database.

2. Bus Network

In a bus network each device in the network handles its own communication control. There is no host computer. All communications control travel along a common connecting cable called a bus. As the information passes along the bus it is examined by each device to see if the information is intended for it.

The bus network is typically used when only a few microcomputers are to be linked together. The bus network is not as efficient as the star network for sharing common resources. However it is less expensive and is in very common use.

3. Ring Network

In a ring network, each device is connected with two other devices forming a ring. There is no central file server or computer. Messages are passed around the ring until they reach correct destination. With microcomputers ring network is the least frequently used arrangement. However it is often used to link mainframes specially over wide geographical areas.

A ring network is useful in a decentralized organization because it makes possible a distributed data processing system i.e. computers can perform processing tasks at their own dispersed locations.

4. Hierarchical Network

This type of networks are also called hybrid network. It consist of several computers linked to a central host computer just like a star network. However these computers are also hosts to other smaller computers or to peripheral devices. The host at the top of the hierarchical network could be mainframe. The computers below the mainframe could be minicomputers and those below microcomputers. This network allows various computers to share database processing programs and different output devices. It is useful in a centralized organizations.

Strategies of Networks

Every network has a strategy or a way of coordinating the sharing of the information and resource. The most common network strategies are terminal, peer-to-peer and client/server systems, terminal network system. In this system processing power is centralized in one large computer, usually the mainframe. The nodes (a node is any device connected to network) connected to this host computer are terminals (a terminal is a input or output device) with little or no processing capability. Most airline reservation systems are terminal systems.

Peer-to-Peer Network System

In a peer-to-peer network, nodes can act both as servers and clients. There are several advantages of using this type of strategy. The networks as inexpensive and easy to install and they usually work well for smaller systems with less than ten nodes. As the number of nodes increases, however the performance of the network declines.

Client/Server Network System

Client/Server network system uses to coordinate and supply services to all other nodes on the network. The server provides access to centralized resources such as databases, applications software and hardware. This strategy is based on specialization. Server nodes coordinate and supply specialized services and client nodes request services.

One advantage of client/server network system is its ability to handle very large networks efficiently. Another advantage is the powerful management software that monitors and controls networks activities. The major disadvantage of it is the high cost of installation and maintenance.

Advantages of Network

Networks provide tremendous benefits. The most compelling advantages of network are as follows.

1. Networks allow users simultaneous access to shared programs and data.

2. Network also allows users to share peripheral devices such as printers and hard disks.

3. Network usually includes the capacity to send e-mail and many e-mail systems let users to attach files to their messages.

4. Connecting computers to form a network makes it easier to perform backups of the data on all the network hard disks.

Types of Networks

Communications differ in geographical size. Three important types are LANs, MANs, WANs.

Local Area Networks (LANs)

Network with computers and peripherals devices in close proximity within the same building are called local area networks (LANs).

The figure shows an example of a LAN. This type of arrangement has two benefits.

1. People can share different equipment, which lowers the cos of equipment.

2. LAN also features a network gateway. i.e. a LAN may be linked to other LANs or to large networks in this manner.

Metropolitan Area Network (MANs)

These network are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones.

Wide Area Network (WANs)

Wide area networks are countrywide and worldwide networks. Among other kinds of channels they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet. Which allows users to connect to other users and facilities worldwide.

Uses of Internet

The most common uses of Internet are

1. Communicating

Sending and receiving e-mail is the most popular internet activity. You can send and receive e-mail to and from you friends and family located almost anywhere in the world. You can join an listen to discussions and debates on a wide variety of special interest topics.

2. Shopping

One of the fastest growing applications of Interest is electronic commerce. You can visit a cyber mall for making purchases.

3. Researching

Internet provides you to have one of the world's largest libraries available from home.

4. Entertainment

Do you like music, the moves and reading or playing computer games? You can find them all on Internet waiting for you to locate and enjoy.

What are the characteristics of client/server architecture

The basic characteristics of client/server architectures are:

1) Combination of a client or front-end portion that interacts with the user, and a server or back-end portion that interacts with the shared resource. The client process contains solution-specific logic and provides the interface between the user and the rest of the application system. The server process acts as a software engine that manages shared resources such as databases, printers, modems, or high powered processors.

2) The front-end task and back-end task have fundamentally different requirements for computing resources such as processor speeds, memory, disk speeds and capacities, and input/output devices.

3) The environment is typically heterogeneous and multivendor. The hardware platform and operating system of client and server are not usually the same.Client and server processes communicate through a well-defined set of standard application program interfaces (API's) and RPC's.

4) An important characteristic of client-server systems is scalability. They can be scaled horizontally or vertically. Horizontal scaling means adding or removing client workstations with only a slight performance impact. Vertical scaling means migrating to a larger and faster server machine or multiservers.

What is the full form of ISDN? Explain use of ISDN in Internet

Integrated Services Digital Network (ISDN) is an upgraded phone line that can be used for faster Internet access and for regular voice calls. Using one line, you can talk on the phone while you’re surfing the Web. ISDN is all digital, which means that data doesn’t have to be converted to an analog signal for transmission.

The ISDN service intended for residential use is Basic Rate Interface (BRI). On one ISDN line, BRI provides two 64Kbps channels, or B channels, and one 16Kbps channel, or D channel.

The D channel is mostly used for signaling—for instance, to indicate that the line is busy.

The B channels are where the action is. When the B channels are combined, you have a 128Kbps line to the Internet. That’s over twice the speed of the fastest analog modem, 56Kbps. If you want to talk on the phone or send a fax, your Internet access drops down to one 64Kbps B channel while the other B channel is used for voice.

How does a Token-Passing Protocol works

The token-passing protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.

Logical Ring Physical Star topology for Token-Passing Standard.

It is sure that any break in the ring at any point will interrupt communications for all machines. To solve this problem, IBM developed a modified ring topology, which they called the logical ring physical star. The central point of the physical star configuration is Token Ring hub called the multi-station access unit (MSAU, pronounced as masow). Workstations and servers attached to the MSAU through special STP adapter cables. IBM converted stars into a logical ring by connecting all MSAU hubs together through special ring-in (RI) and ring-out (RO) ports.

Advantages of Token Ring.

Here are Token ring's most useful advantages:

a. It offers excellent throughput under high-load conditions.

b. Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with IBM's broader connectivity strategies.

c. It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration and may now be used with UTP cabling.

d. It has the most reliable protocol (token-passing), the most trouble-free configuration (physical star) and the fastest connectivity scheme (r or 16 mb/s).

Disadvantages of Token Ring.

Few of the disadvantages of Token Ring are:

a. Token Ring is very expensive. All topology components cost much more than other more popular standards.

b. It is relatively proprietary. Token Ring's complexity is built into the hardware components. This means hat you need to choose a manufacturer and stick with it.

c. Engineers must have considerable expertise to manage and troubleshoot token ring components.

What is Proxy Server

A server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.

Proxy servers have two main purposes:

# Improve Performance: Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as America Online, MSN and Yahoo, for example, employ an array of proxy servers.

# Filter Requests: Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

What is a Router in Computer Network

Router is used to send data to the next network. Routers are Computer Network device that is used for  delivering and forwarding information.

Types of Routers

Many kinds of Routers are present in the current market that are depending on the need of the any enterprises. Cisco is the major manufacturer of router mostly Cisco router are used to set up network of large corporation and even of the ISPs. Broadly Routers are divided into three categories that depending upon the corporate needs.

1. Internet connectivity routers

These routers are used in Border Gateway Protocol for exchange information. These type of routers are further divided into four more categories.

1.1. Edge router

A Edge router or edge device is routes data packets between LANs and an Asynchronous Transfer Mode (ATM) network.

1.2. Subscriber edge router (SER)

Subscriber edge router (SER) Also known as Customer Edge router.Customer Edge router use EBGP protocol, it used in (enterprise) organization.

1.3. Inter provider border router

Inter provider border router are used for Interconnecting ISPs. Inter provider border router use BGP protocol to speake.

1.4. Core router

When a router become the integral part of the LAN(Local Area Network) is called core router. Core router uses internal BGP protocol.Core routers have specialized functions in VPN,that is based on a combination of BGP and Multi-Protocol Label Switching protocols.

One Another Type of Router is SOHO routers. It is used for connection other networks in small geographical area it is known as SOHO connectivity.

How Routers Works

Routers are interconnectivity devices that is used to transfer the datum packets along networks by visualizing the networks path. Routers visualizing the networks path to many networks such as Electronic networks, Transport networks and phone networks. Two ways are exist for routers operation using either control plane or forwarding plane. In control plane the router sends the precise data packets to their specific location. On the other hand in forwarding plane router does not remember the sending or receiving information about the packets.

Advantages of Routers

Routers route the data in an organized way. Routers generate a reliable connection between hosts. Routers is used for alternatively incase the main is fail to transfer data.