Directing Traffic

he router is the only device that sees every message sent by any computer on either of the company's networks. When the animator in our example sends a huge file to another animator, the router looks at the recipient's address and keeps the traffic on the animator's network. When an animator, on the other hand, sends a message to the bookkeeper asking about an expense-account check, then the router sees the recipient's address and forwards the message between the two networks. One of the tools a router uses to decide where a packet should go is a configuration table. A configuration table is a collection of information, including:

• Information on which connections lead to particular groups of addresses
• Priorities for connections to be used
• Rules for handling both routine and special cases of traffic

A configuration table can be as simple as a half-dozen lines in the smallest routers, but can grow to massive size and complexity in the very large routers that handle the bulk of Internet messages.

A router, then, has two separate but related jobs:

• The router ensures that information doesn't go where it's not needed. This is crucial for keeping large volumes of data from clogging the connections of "innocent bystanders."
• The router makes sure that information does make it to the intended destination.

In performing these two jobs, a router is extremely useful in dealing with two separate computer networks. It joins the two networks, passing information from one to the other and, in some cases, performing translations of various protocols between the two networks. It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other. As the number of networks attached to one another grows, the configuration table for handling traffic among them grows, and the processing power of the router is increased. Regardless of how many networks are attached, though, the basic operation and function of the router remains the same. Since the Internet is one huge network made up of tens of thousands of smaller networks, its use of routers is an absolute necessity.

Router - message delivery

When you send e-mail to a friend on the other side of the country, how does the message know to end up on your friend's computer, rather than on one of the millions of other computers in the world? Much of the work to get a message from one computer to another is done by routers, because they're the crucial devices that let messages flow between networks, rather than within networks.

Let's look at what a very simple router might do. Imagine a small company that makes animated 3-D graphics for local television stations. There are 10 employees of the company, each with a computer. Four of the employees are animators, while the rest are in sales, accounting and management. The animators will need to send lots of very large files back and forth to one another as they work on projects. To do this, they'll use a network.

When one animator sends a file to another, the very large file will use up most of the network's capacity, making the network run very slowly for other users. One of the reasons that a single intensive user can affect the entire network stems from the way that Ethernet works. Each information packet sent from a computer is seen by all the other computers on the local network. Each computer then examines the packet and decides whether it was meant for its address. This keeps the basic plan of the network simple, but has performance consequences as the size of the network or level of network activity increases. To keep the animators' work from interfering with that of the folks in the front office, the company sets up two separate networks, one for the animators and one for the rest of the company. A router links the two networks and connects both networks to the Internet.

Ethernet 802.3

You may have heard the term 802.3 used in place of or in conjunction with the term Ethernet. "Ethernet" originally referred to a networking implementation standardized by Digital, Intel and Xerox. (For this reason, it is also known as the DIX standard.)

In February 1980, the Institute of Electrical and Electronics Engineers, or IEEE (pronounced "I triple E"), created a committee to standardize network technologies. The IEEE titled this the 802 working group, named after the year and month of its formation. Subcommittees of the 802 working group separately addressed different aspects of networking. The IEEE distinguished each subcommittee by numbering it 802.X, with X representing a unique number for each subcommittee. The 802.3 group standardized the operation of a CSMA/CD network that was functionally equivalent to the DIX Ethernet.

Ethernet and 802.3 differ slightly in their terminology and the data format for their frames, but are in most respects identical. Today, the term Ethernet refers generically to both the DIX Ethernet implementation and the IEEE 802.3 standard.

Home Networking Work

The two most popular home network types are wireless and Ethernet networks. In both of these types, the router does most of the work by directing the traffic between the connected devices. By connecting a router to your dial-up, DSL or cable modem, you can also allow multiple computers to share one connection to the Internet.

If you're going to connect your network to the Internet, you'll need a firewall. A firewall is simply a hardware device or software program that protects your network from malicious users and offensive Web sites, keeping hackers from accessing or destroying your data. Although they're essential for businesses looking to protect large amounts of information, they're just as necessary for someone setting up a home network, since a firewall will secure transactions that might include Social Security numbers, addresses, phone numbers and credit card numbers. Most routers combine wireless and Ethernet technology and also include a hardware firewall.

Many software firewalls installed onto your computer block all incoming information by default and prompt you for permission to allow the information to pass. In this way, a software firewall can learn which types of information you want to allow into your network. Symantec, McAfee and ZoneAlarm are popular companies that produce software-based firewalls. These companies usually offer some free firewall protection as well as advanced security that you can buy.

Home Networking

A home network is simply a method of allowing computers to communicate with one another. If you have two or more computers in your home, a network can let them share:

• Files and documents
• An Internet connection
• Printers, print servers and scanners
• Stereos, TVs and game systems
• CD burners

The different network types use different hardware, but they all have the same essential components:

• More than one computer
• Hardware (such as a router) and software (either built in to the operating system or as a separate application) to coordinate the exchange of information
• A path for the information to follow from one computer to another

Data Packet

Continue :

Depending on the type of network, packets may be referred to by another name:

• frame
• block
• cell
• segment

Most packets are split into three parts:

• header - The header contains instructions about the data carried by the packet. These instructions may include:
  • Length of packet (some networks have fixed-length packets, while others rely on the header to contain this information)
  • Synchronization (a few bits that help the packet match up to the network)
  • Packet number (which packet this is in a sequence of packets)
  • Protocol (on networks that carry multiple types of information, the protocol defines what type of packet is being transmitted: e-mail, Web page, streaming video)
  • Destination address (where the packet is going)
  • Originating address (where the packet came from)

Data Packet

On the Internet, the network breaks an e-mail message into parts of a certain size in bytes. These are the packets. Each packet carries the information that will help it get to its destination -- the sender's IP address, the intended receiver's IP address, something that tells the network how many packets this e-mail message has been broken into and the number of this particular packet. The packets carry the data in the protocols that the Internet uses: Transmission Control Protocol/Internet Protocol (TCP/IP). Each packet contains part of the body of your message. A typical packet contains perhaps 1,000 or 1,500 bytes.

Each packet is then sent off to its destination by the best available route -- a route that might be taken by all the other packets in the message or by none of the other packets in the message. This makes the network more efficient. First, the network can balance the load across various pieces of equipment on a millisecond-by-millisecond basis. Second, if there is a problem with one piece of equipment in the network while a message is being transferred, packets can be routed around the problem, ensuring the delivery of the entire message.

Ethernet Medium

Since a signal on the Ethernet medium reaches every attached node, the destination address is critical to identify the intended recipient of the frame.

For example, in the figure above, when computer B transmits to printer C, computers A and D will still receive and examine the frame. However, when a station first receives a frame, it checks the destination address to see if the frame is intended for itself. If it is not, the station discards the frame without even examining its contents.

One interesting thing about Ethernet addressing is the implementation of a broadcast address. A frame with a destination address equal to the broadcast address (simply called a broadcast, for short) is intended for every node on the network, and every node will both receive and process this type of frame.

Ethernet Terminology

Ethernet follows a simple set of rules that govern its basic operation. To better understand these rules, it is important to understand the basics of Ethernet terminology.

• Medium - Ethernet devices attach to a common medium that provides a path along which the electronic signals will travel. Historically, this medium has been coaxial copper cable, but today it is more commonly a twisted pair or fiber optic cabling.

• Segment - We refer to a single shared medium as an Ethernet segment.

• Node - Devices that attach to that segment are stations or nodes.

• Frame - The nodes communicate in short messages called frames, which are variably sized chunks of information.

Frames are analogous to sentences in human language. In English, we have rules for constructing our sentences: We know that each sentence must contain a subject and a predicate. The Ethernet protocol specifies a set of rules for constructing frames. There are explicit minimum and maximum lengths for frames, and a set of required pieces of information that must appear in the frame. Each frame must include, for example, both a destination address and a source address, which identify the recipient and the sender of the message. The address uniquely identifies the node, just as a name identifies a particular person. No two Ethernet devices should ever have the same address.

ETHERNET

Ethernet is a local area technology, with networks traditionally operating within a single building, connecting devices in close proximity. At most, Ethernet devices could have only a few hundred meters of cable between them, making it impractical to connect geographically dispersed locations. Modern advancements have increased these distances considerably, allowing Ethernet networks to span tens of kilometers.

Type of Viruses

There are various types of viruses :

Boot viruses place (some of) their code in the disk sector whose code the machine will automatically execute when booting. Thus, when an infected machine boots, the virus loads and runs. After boot viruses are finished loading, they usually load the original boot code, which they have previously moved to another location, or take other measures to ensure the machine appears to boot normally.
File viruses attach to 'program files' (files containing executable or interpretable code) in such a way that when you run the infected program, the virus code executes. Usually the virus code is added in such a way that it executes first, although this is not strictly necessary. After the virus code has finished loading and executing, it will normally load and execute the original program it has infected, or call the function it intercepted, so as to not arouse the user's suspicion.
Macro viruses are really just a type of file virus, but a particularly 'successful' type. They copy their macros to templates and/or other application document files. Although 'auto macros' were almost exclusively used by early macro viruses (often to ensure the virus' code is the first to execute when infected templates or documents were opened), several other mechanisms are also available - in fact, some of these, such as taking over standard internal functions of the host application (say the 'File Save' command) and installing default event handlers are probably more commonly used these days.
Script viruses also became quite successful around the beginning of this century. This was mainly due to the increase in machines running Windows Scripting Host, which was first installed by default in Windows 98 and 2000 and with Internet Explorer 5.0 and later versions. Representing new types of 'program file', but with icons more like that of 'safe' text files, standalone Visual Basic Script (VBS) and JavaScript (JS) programs became a popular target of the writers of mass mailing viruses.
Companion viruses take advantage of features of the operating system to be executed, rather than directly infecting programs or boot sectors. Under DOS and Windows, when you execute the command 'ABC', the rule is that ABC.COM executes before ABC.EXE (in the rare cases where both files exist). Thus, a companion virus could place its code in a COM file with its first name matching that of an existing EXE file. When the user next executed the 'ABC' command, the virus' ABC.COM program would be run (usually the virus would launch ABC.EXE once its code was finished so as not to arouse suspicion). This is known as the 'execution preference companion' method, but several other forms of companion infection are also possible.

Computer Viruses

About Viruses :

Some viruses display obvious symptoms, and some cause damage to files in a system they have infected. A non-damaging virus is still a virus, not a prank and, other things being equal, viruses without obvious symptoms are more likely to spread further and persist longer than those that rapidly draw attention to themselves.

There are no 'good' viruses, simply because a virus is code that was not intentionally installed by the user. Users must be able to control their computers, and that requires that they have the power to install and remove software; that no software is installed, modified, or removed without their knowledge and permission. A virus is surreptitiously self-installed. It may modify other software in the system without user awareness, and removal can be difficult and costly.

Many viruses cause intentional damage. But many more cause damage that may not have been intended by the virus writer. For instance, when a virus finds itself in a very different environment than that for which it was written, what was intended to be a non-destructive virus can prove very destructive. A good case in point is the boot virus. Few, if any, boot viruses contain code to damage computers running Windows NT however, with many boot viruses, when they infect an NT machine system recovery can be quite tricky.

Even if a virus causes no direct damage to your computer, your inexperience with viruses can mean that damage occurs during the removal process. Many organizations have shredded floppies, deleted files, and done low-level formats of hard disks in their efforts to remove viruses. Even when removal is done perfectly, with no damage to the infected system or files, it is not normally done when the machine is first infected, and the virus in that machine has had a few weeks to spread. The social costs of infection include a loss of reputation and good will. This last point is increasingly significant recently with the rapid increase in network-aware and data stealing viruses.

VIRUSES - About - Threats - Worms - Trojan Horses - Anti Virus

What is Computer Virus:

A computer virus is a program that explicitly copies itself. This may lead to it spreading from machine to machine and is typically done without the user's knowledge or permission. Viruses, by definition, add their code to your system in such a way that when the infected part of the system executes, the virus does also.

NETWORK SECURITY TOOLS

Network security tools include:
Antivirus software packages : These packages counter most virus threats if regularly updated and correctly maintained.
Secure network infrastructure : Switches and routers have hardware and software features that support secure connectivity, perimeter security, intrusion protection, identity services, and security management.
Dedicated network security hardware and software-Tools such as firewalls and intrusion detection systems provide protection for all areas of the network and enable secure connections.
Virtual private networks : These networks provide access control and data encryption between two different computers on a network. This allows remote workers to connect to the network without the risk of a hacker or thief intercepting data.
Identity services : These services help to identify users and control their activities and transactions on the network. Services include passwords, digital certificates, and digital authentication keys.
Encryption : Encryption ensures that messages cannot be intercepted or read by anyone other than the authorized recipient.
Security management : This is the glue that holds together the other building blocks of a strong security solution.

NETWORK SECURITY TREAT

Threats to network security include:

Viruses : Computer programs written by devious programmers and designed to replicate themselves and infect computers when triggered by a specific event
Trojan horse programs : Delivery vehicles for destructive code, which appear to be harmless or useful software programs such as games
Vandals : Software applications or applets that cause destruction
Attacks : Including reconnaissance attacks (information-gathering activities to collect data that is later used to compromise networks); access attacks (which exploit network vulnerabilities in order to gain entry to e-mail, databases, or the corporate network); and denial-of-service attacks (which prevent access to part or all of a computer system)
Data interception : Involves eavesdropping on communications or altering data packets being transmitted
Social engineering : Obtaining confidential network security information through nontechnical means, such as posing as a technical support person and asking for people's passwords

NETWORK SECURITY MANAGEMENT

What is network security all about

The networks are computer networks, both public and private, that are used every day to conduct transactions and communications among businesses, government agencies and individuals. The networks are comprised of "nodes", which are "client" terminals (individual user PCs) and one or more "servers" and/or "host" computers. They are linked by communication systems, some of which might be private, such as within a company, and others which might be open to public access. The obvious example of a network system that is open to public access is the Internet, but many private networks also utilize publicly-accessible communications. Today, most companies' host computers can be accessed by their employees whether in their offices over a private communications network, or from their homes or hotel rooms while on the road through normal telephone lines.

Network security involves all activities that organizations, enterprises, and institutions undertake to protect the value and ongoing usability of assets and the integrity and continuity of operations. An effective network security strategy requires identifying threats and then choosing the most effective set of tools to combat them.

ipv6 addresses

The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the Internet's addressing capability. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This next generation of the Internet Protocol, aimed to replace IPv4 on the Internet, was eventually named Internet Protocol Version 6 (IPv6)^[3] The address size was increased from 32 to 128 bits (16 bytes), which, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically, the new address space provides the potential for a maximum of 2¹²⁸, or about 3.403 × 10³⁸ unique addresses.

ipv4

IPv4 uses 32-bit (4-byte) addresses, which limits the address space to 4,294,967,296 (2³²) possible unique addresses. However, IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses). This reduces the number of addresses that can be allocated as public Internet addresses, and as the number of addresses available is consumed, an IPv4 address shortage appears to be inevitable in the long run. This limitation has helped stimulate the push towards IPv6, which is currently in the early stages of deployment and is currently the only offering to replace IPv4.

IPv4 addresses are usually represented in dot-decimal notation (four numbers, each ranging from 0 to 255, separated by dots, e.g. 208.77.188.166). Each part represents 8 bits of the address, and is therefore called an octet. It is possible, although less common, to write IPv4 addresses in binary or hexadecimal. When converting, each octet is treated as a separate number. (So 255.255.0.0 in dot-decimal would be FF.FF.00.00 in hexadecimal.)

ip address

An Internet Protocol (IP) address is a numerical identification (logical address) that is assigned to devices participating in a computer network utilizing the Internet Protocol for communication between its nodes.^[1] Although IP addresses are stored as binary numbers, they are usually displayed in human-readable notations,such as 208.77.188.166 (for IPv4), and 2001:db8:0:1234:0:567:1:1 (for IPv6). The role of the IP address has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there." ^[2]

The original designers of TCP/IP defined an IP address as a 32-bit number^[1] and this system, now named Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the resulting depletion of the address space, a new addressing system (IPv6), using 128 bits for the address, was developed (RFC 1883).

IPV6 and IPV4

IPv6 is short for "Internet Protocol Version 6". IPv6 is the "next generation" protocol designed by the IETF to replace the current version Internet Protocol, IP Version 4 ("IPv4").

Most of today's internet uses IPv4, which is now nearly twenty years old. IPv4 has been remarkably resilient in spite of its age, but it is beginning to have problems. Most importantly, there is a growing shortage of IPv4 addresses, which are needed by all new machines added to the Internet.

IPv6 fixes a number of problems in IPv4, such as the limited number of available IPv4 addresses. It also adds many improvements to IPv4 in areas such as routing and network autoconfiguration. IPv6 is expected to gradually replace IPv4, with the two coexisting for a number of years during a transition period.