Related Links



Informative Articles

Business Continuity and Disaster Recovery - The Business Continuity and Disaster Recovery Plan
Essentially, the plan addresses the who, what, where, why and when of recovery. Goal number one is to reduce the risk profile of the business. Goal two is to be well prepared so the impact of any disruption is minimized. Overall, the objective...

Choosing data recovery company
Choosing a data recovery company. There are many different factors to consider when choosing a data recovery company. All of them may have strong advantages in some areas but be weaker or less efficient in others. If this is your first time...

Computer Viruses - the basics
In its simplest terms a virus is a disruptive computer code period! A computer virus almost always repeats itself and spreads by attaching itself to other files. Viruses can be made to host a number of harmful things on any computer...

Hard Dive Failure: What Is A Head Crash?
No one likes the thought of losing all of their valuable data, but a hard drive head crash is a definite data destroyer. While a recovery is possible in most cases, sometimes destruction of the platters is so severe that the magnetic material is...

Using SANRAD V-Switch as the VSS hardware provider for Windows backups
Introduction Many Microsoft Window applications (like Exchange, MS-SQL, etc) are critical to the daily core functionality for many companies and organizations. Managing the data backup for these applications presents new challenges for...


Introduction to Intranets

What exactly is an intranet? It's one of those terms that's more thrown around than understood, and has become more of a buzzword than a commonly understood idea. Simply put, an intranet is a private network with Internet technology used as the underlying architecture. An intranet is built using the Internet's TCP/IP protocols for communications. TCP/IP protocols can be run on many hardware platforms and cabling schemes. The underlying hardware is not what makes an intranet-it's the software protocols that matter.

Intranets can co-exist with other local area networking technology. In many companies, existing "legacy systems" including mainframes, Novell networks, minicomputers, and various databases, are being integrated into an intranet. A wide variety of tools allow this to happen. Common Gateway Interface (CGI) scripting is often used to access legacy databases from an intranet. The Java programming language can be used to access legacy databases as well.

With the enormous growth of the Internet, an increasing number of people in corporations use the Internet for communicating with the outside world, for gathering information, and for doing business. It didn't take long for people to recognize that the components that worked so well on the Internet could be equally valuable internally and that is why intranets are becoming so popular. Some corporations do not have TCP/IP networks, the protocol required to access the resources of the Internet. Creating an intranet in which all the information and resources can be used seamlessly has many benefits. TCP/IP-based networks make it easy for people to access the network remotely, such as from home or while traveling. Dialing into an intranet in this way is much like connecting to the Internet, except that you're connecting to a private network instead of to a public Internet provider. Interoperability between networks is another substantial bonus.

Security systems separate an intranet from the Internet. A company's intranet is protected by firewalls-hardware and software combinations that allow only certain people to access the intranet for specific purposes.

Intranets can be used for anything that existing networks are used for-and more. The ease of publishing information on the World Wide Web has made them popular places for posting corporate information such as company news or company procedures. Corporate databases with easy-to-build front-ends use the Web and programming languages such as Java.

Intranets allow people to work together more easily and more effectively. Software known as groupware is another important part of intranets. It allows people to collaborate on projects; to share information; to do videoconferencing; and to establish secure procedures for production work. Free server and client software and the multitude of services, like newsgroups, stimulated the Internet's growth. The consequence of that growth stimulated and fueled the growth of intranets. The ease with which information can be shared, and with which people can communicate with one another will continue to drive the building of intranets.

A Global View of an Intranet

An intranet is a private corporate or educational network that uses the Internet's TCP/IP protocols for its underlying transport. The protocols can run on a variety of network hardware, and can also co-exist with other network protocols, such as IPX. People from inside an intranet can get at the larger Internet resources, but those on the Internet cannot get into the intranet, which allows only restricted access from the Internet.

  • Videoconferencing is an important application that requires sending massive quantities of data. Intranets can be built using components that allow the extremely high bandwidths required for transferring such information.

  • Often an intranet is composed of a number of different networks inside a corporation that all communicate with one another via TCP/IP. These separate networks are often referred to as subnets.

  • Software that allows people to communicate with each other via e-mail and public message boards and to collaborate on work using workgroup software is among the most powerful intranet programs. Applications that allow different corporate departments to post information, and for people to fill out corporate forms, such as time sheets, and for tapping into corporate financial information are very popular.

  • Much of the software used on intranets is standard, off-the-shelf Internet software such as the Netscape Navigator and the Microsoft Explorer Web browsers. And customized programs are often built, using the Java programming language and CGI scripting.

  • Intranets can also be used to allow companies to do business-to-business transactions, such as ordering parts, sending invoices, and making payments. For extra security, these intranet-to-intranet transactions need never go out over the public Internet, but can travel over private leased lines instead.

  • Intranets are a powerful system for allowing a company to do business online, for example, to allow anyone on the Internet to order products. When someone orders a product on the Internet, information is sent in a secure manner from the public Internet to the company's intranet, where the order is processed and completed.

  • In order to protect sensitive corporate information, and to ensure that hackers don't damage computer systems and data, security barriers called firewalls protect an intranet from the Internet. Firewall technology uses a combination of routers, servers and other hardware and software to allow people on an intranet to use Internet resources, but blocks outsiders from getting into the intranet.

  • Many intranets have to connect to "legacy systems"-hardware and databases that were built before an intranet was constructed. Legacy systems often use older technology not based on the intranet's TPC/IP protocols. There are a variety of ways in which intranets can tie to legacy systems. A common way is to use CGI scripts to access the database information and pour that data into HTML formatted text, making it available to a Web browser.

  • Information sent across an intranet is sent to the proper destination by routers, which examine each TCP/IP packet for the IP address and determine the packet's destination. It then sends the packet to the next router closest to the destination. If the packet is to be delivered to an address on the same subnetwork of the intranet it was sent from, the packet may be able to be delivered directly without having to go through any other routers. If it is to be sent to another subnetwork on the intranet, it will be sent to another internal router address. If the packet is to be sent to a destination outside the intranet-in other words, to an Internet destination-the packet is sent to a router that connects to the Internet

How TCP/IP and IPX Work on Intranets

What distinguishes an intranet from any other kind of private network is that it is based on TCP/IP-the same protocols that apply to the Internet. TCP/IP refers to two protocols that work together to deliver data: the Transmission Control Protocol (TCP) and the Internet Protocol (IP). When you send information across an intranet, the data is broken into small packets. The packets are sent independently through a series of switches called routers. Once all the packets arrive at their destination, they are recombined into their original form. The Transmission Control Protocol breaks the data into packets and recombines them on the receiving end. The Internet Protocol handles the routing of the data and makes sure it gets sent to the proper destination.

  1. In some companies, there may be a mix of TCP/IP-based intranets and networks based on other networking technology, such as NetWare. In that instance, the TCP/IP technology of an intranet can be used to send data between NetWare or other networks, using a technique called IP tunneling. In this instance, we'll look at data being sent from one NetWare network to another, via an intranet. NetWare networks use the IPX (Internet Packet Exchange) protocol as a way to deliver data-and TCP/IP networks can't recognize that protocol. To get around this, when an IPX packet is to be sent across an intranet, it is first encapsulated inside an IP packet by a NetWare server specifically for and dedicated to providing the IP transport mechanism for IPX packets.

  2. Data sent within an intranet must be broken up into packets of less than 1,500 characters each. TCP breaks the data into packets. As it creates each packet, it calculates and adds a checksum to the packet. The checksum is based on the byte values, that is, the precise amount of data in the packet.

  3. Each packet, along with the checksum, is put into separate IP wrappers or "envelopes." These wrappers contain information that details exactly where on the intranet-or the Internet-the data is to be sent. All of the wrappers for a given piece of data have the same addressing information so that they can all be sent to the same location for reassembly.

  4. The packets travel between networks by intranet routers. Routers examine all IP wrappers and look at their addresses. These routers determine the most efficient path for sending each packet to its final destination. Since the traffic load on an intranet often changes, the packets may be sent along different routes, and the packets may arrive out of order. If the router sees the address is one located inside the intranet, the packet may be sent directly to its destination, or it may instead be sent to another router. If the address is located out on the Internet, it will be sent to another router so it can be sent across the Internet.

  5. As the packets arrive at their destination, TCP calculates a checksum for each packet. It then compares this checksum with the checksum that has been sent in the packet. If the checksums don't match, TCP knows that the data in the packet has been corrupted during transmission. It then discards the packet and asks that the original packet be retransmitted.

  6. TCP includes the ability to check packets and to determine that all the packets have been received. When all the non-corrupt packets are received, TCP assembles them into their original, unified form. The header information of the packets relays the sequence of how to reassemble the packets.

  7. An intranet treats the IP packet as it would any other, and routes the packet to the receiving NetWare network. On the receiving NetWare network, a NetWare TCP/IP server decapsulates the IP packet-it discards the IP packet, and reads the original IPX packet. It can now use the IPX protocol to deliver the data to the proper destination.

How the OSI Model Works

A group called the International Standards Organization (ISO) has put together the Open Systems Interconnect (OSI) Reference Model, which is a model that describes seven layers of protocols for computer communications. These layers don't know or care what is on adjacent layers. Each layer, essentially, only sees the reciprocal layer on the other side. The sending application layer sees and talks to the application layer on the destination side. That conversation takes place irrespective of, for example, what structure exists at the physical layer, such as Ethernet or Token Ring. TCP combines the OSI model's application, presentation, and session layers into one which is also called the application layer.

  • The application layer refers to application interfaces, not programs like word processing. MHS (Message Handling Service) is such an interface and it operates at this level of the OSI model. Again, this segmentation and interface approach means that a variety of email programs can be used on an intranet so long as they conform to the MHS standard at this application interface level.

  • The presentation layer typically simply provides a standard interface between the application layer and the network layers. This type of segmentation allows for the great flexibility of the OSI model since applications can vary endlessly, but, as long as the results conform to this standard interface, the applications need not be concerned with any of the other layers.

  • The session layer allows for the communication between sender and destination. These conversations avoid confusion by speaking in turn. A token is passed to control and to indicate which side is allowed to speak. This layer executes transactions, like saving a file. If something prevents it from completing the save, the session layer, which has a record of the original state, returns to the original state rather than allowing a corrupt or incomplete transaction to occur.

  • The transport layer segments the data into acceptable packet sizes and is responsible for data integrity of packet segments. There are several levels of service that can be implemented at this layer, including segmenting and reassembly, error recovery, flow control, and others.

  • The IP wrapper is put around the packet at the network or Internet layer. The header includes the source and destination addresses, the sequence order, and other data necessary for correct routing and rebuilding at the destination.

  • The data-link layer frames the packets-for example, for use with the PPP (Point to Point). It also includes the logical link portion of the MAC sublayer of the IEEE 802.2, 802.3 and other standards.

  • Ethernet and Token Ring are the two most common physical layer protocols. They function at the MAC (Media Access Control) level and move the data over the cables based on the physical address on each NIC (Network Interface Card). The physical layer includes the physical components of the IEEE 802.3 and other specifications.

How TCP/IP Packets Are Processed

Protocols such as TCP/IP determine how computers communicate with each other over networks such as the Internet. These protocols work in concert with each other, and are layered on top of one another in what is commonly referred to as a protocol stack. Each layer of the protocol is designed to accomplish a specific purpose on both the sending and receiving computers. The TCP stack combines the application, presentation, and the session layers into a single layer also called the application layer. Other than that change, it follows the OSI model. The illustration below shows the wrapping process that occurs to transmit data.

  • The TCP application layer formats the data being sent so that the layer below it, the transport layer, can send the data. The TCP application layer performs the equivalent actions that the top three layers of OSI perform: the application, presentation, and session layers.

  • The next layer down is the transport layer, which is responsible for transferring the data, and ensures that the data sent and the data received are in fact the same data-in other words, that there have been no errors introduced during the sending of the data. TCP divides the data it gets from the application layer into segments. It attaches a header to each segment. The header contains information that will be used on the receiving end to ensure that the data hasn't been altered en route, and that the segments can be properly recombined into their original form.

  • The third layer prepares the data for delivery by putting them into IP datagrams, and determining the proper Internet address for those datagrams. The IP protocol works in the Internet layer, also called the network layer. It puts an IP wrapper with a header onto each segment. The IP header includes information such as the IP address of the sending and receiving computers, and the length of the datagram, and the sequence order of the datagram. The sequence order is added because the datagram could conceivably exceed the size allowed for network packets, and so would need to be broken into smaller packets. Including the sequence order will allow them to be recombined properly.

  • The Internet layer checks the IP header and checks to see whether the packet is a fragment. If it is, it puts together fragments back into the original datagram. It strips off the IP header, and then sends the datagram to the transport layer.

  • The transport layer looks at the remaining header to decide which application layer protocol-TCP or UDP-should get the data. Then the proper protocol strips off the header and sends the data to the receiving application.

  • The application layer gets the data and performs, in this case, an HTTP request.

  • The next layer down, the data link layer, uses protocols such as the Point-to-Point Protocol (PPP) to put the IP datagram into a frame. This is done by putting a header-the third header, after the TCP header and the IP header-and a footer around the IP datagram to fra-me it. Included in the frame header is a CRC check that checks for errors in the data as the data travels over the network.

  • The data-link layer ensures that the CRC for the frame is right, and that the data hasn't been altered while it was sent. It strips off the frame header and the CRC, and sends the frame to the Internet layer.

  • On the receiving computer, the packet travels through the stack, but in the opposite order from which the packet was created. In other words, it starts at the bottom layer, and moves its way up through the protocol stack. As it moves up, each layer strips off the header information that was added by the TCP/IP stack of the sending computer.

  • The final layer is the physical network layer, which specifies the physical characteristics of the network being used to send data. It describes the actual hardware standards, such as the Ethernet specification. The layer receives the frames from the data link layer, and translates the IP addresses there into the hardware addresses required for the specific network being used. Finally, the layer sends the frame over the network.

  • The physical network layer receives the packet. It translates the hardware address of the sender and receiver into IP addresses. Then it sends the frame up to the data link layer.

How Bridges Work

Bridges are hardware and software combinations that connect different parts of a single network, such as different sections of an intranet. They connect local area networks (LANs) to each other. They are generally not used, however, for connecting entire networks to each other, for example, for connecting an intranet to the Internet, or an intranet to an intranet, or to connect an entire subnetwork to an entire subnetwork. To do that, more sophisticated pieces of technology called routers are used.

  1. When there is a great amount of traffic on an Ethernet local area network, packets can collide with one another, reducing the efficiency of the network, and slowing down network traffic. Packets can collide because so much of the traffic is routed among all the workstations on the network.

  2. In order to cut down on the collision rate, a single LAN can be subdivided into two or more LANs. For example, a single LAN can be subdivided into several departmental LANs. Most of the traffic in each departmental LAN stays within the department LAN, and so it needn't travel through all the workstations on all the LANs on the network. In this way, collisions are reduced. Bridges are used to link the LANs. The only traffic that needs to travel across bridges is traffic bound for another LAN. Any traffic within the LAN need not travel across a bridge.

  3. Each packet of data on an intranet has more information in it than just the IP information. It also includes addressing information required for other underlying network architecture, such as for an Ethernet network. Bridges look at this outer network addressing information and deliver the packet to the proper address on a LAN

  4. Bridges consult a learning table that has the addresses of all the network nodes in it. If a bridge finds that a packet belongs on its own LAN, it keeps the packet inside the LAN. If it finds that the workstation is on another LAN, it forwards the packet. The bridge constantly updates the learning table as it monitors and routes traffic.

  5. Bridges can connect LANs in a variety of different ways. They can connect LANs using serial connections over traditional phone lines and modems, over ISDN lines, and over direct cable connections. CSU/DSU units are used to connect bridges to telephone lines for remote connectivity.

  6. Bridges and routers are sometimes combined into a single product called a brouter. A brouter handles both bridging and routing tasks. If the data needs to be sent only to another LAN on the network or subnetwork, it will act only as a bridge delivering the data based on the Ethernet address. If the destination is another network entirely, it will act as a router, examining the IP packets and routing the data based on the IP address.

How Intranet Routers Work

Just as routers direct traffic on the Internet, sending information to its proper destination, and routers on an intranet perform the same function. Routers-equipment that is a combination of hardware and software-can send the data to a computer on the same sub network inside the intranet, to another network on the intranet, or outside to the Internet. They do this by examining header information in IP packets, and then sending the data on its way. Typically, a router will send the packet to the next router closest to the final destination, which in turn sends it to an even closer router, and so on, until the data reaches its intended recipient.

  1. A router has

    input ports for receiving IP packets, and output ports for sending those packets toward their destination. When a packet comes to the input port, the router examines the packet header, and checks the destination in it against a routing table-a database that tells the router how to send packets to various destinations.

  2. Based on the information in the routing table, the packet is sent to a particular output port, which sends the packet to the next closest router to the packet's destination.

  3. If packets come to the input port more quickly than the router can process them, they are sent to a holding area called an input queue. The router then processes packets from the queue in the order they were received. If the number of packets received exceeds the capacity of the queue (called the length of the queue), packets may be lost. When this happens, the TCP protocol on the sending and receiving computers will have the packets re-sent.

  4. In a simple intranet that is a single, completely self-contained network, and in which there are no connections to any other network or the intranet, only minimal routing need be done, and so the routing table in the router is exceedingly simple with very few entries, and is constructed automatically by a program called ifconfig.

  5. In a slightly more complicated intranet which is composed of a number of TCP/IP-based networks, and connects to a limited number of TCP/IP-based networks, static routing will be required. In static routing, the routing table has specific ways of routing data to other networks. Only those pathways can be used. Intranet administrators can add routes to the routing table. Static routing is more flexible than minimal routing, but it can't change routes as network traffic changes, and so isn't suitable for many intranets.

  6. In more complex intranets, dynamic routing will be required. Dynamic routing is used to permit multiple routes for a packet to reach its final destination. Dynamic routing also allows routers to change the way they route information based on the amount of network traffic on some paths and routers. In dynamic routing, the routing table is called a dynamic routing table and changes as network conditions change. The tables are built dynamically by routing protocols, and so constantly change according to network traffic and conditions.

  7. There are two broad types of routing protocols: interior and exterior. Interior routing protocols are typically used on internal routers inside an intranet that routes traffic bound only for inside the intranet. A common interior routing protocol is the Routing Information Protocol (RIP). Exterior protocols are typically used for external routers on the Internet. AĘcommon exterior protocol is the Exterior Gateway Protocol (EGP).

Intranets come in different sizes. In a small company, an intranet can be composed of only a handful of computers. In a medium-sized business, it may include dozens or hundreds of computers. And in a large corporation, there may be thousands of computers spread across the globe, all connected to a single intranet. When intranets get large, they need to be subdivided into individual subnets or subnetworks.

To understand how subnetting works, you first need to understand IP addresses. Every IP address is a 32-bit numeric address that uniquely identifies a network and then a specific host on that network. The IP address is divided into two sections: the network section, called the netid, and the host section, called the hostid.

Each 32-bit IP address is handled differently, according to what class of network the address refers to. There are three main classes of network addresses: Class A, Class B, and Class C. In some classes, more of the 32-bit address space is devoted to the netid, while in others, more of the address space is devoted to the hostid. In a Class A network, the netid is composed of 8 bits, while the hostid is composed of 24 bits. In a Class B network, both the netid and the hostid are composed of 16 bits. In a Class C network, the netid is composed of 24 bits, while the hostid is composed of 8 bits. There's a simple way of knowing what class a network is in. If the first number of the IP address is less than 128, the network is a Class A address. If the first number is from 128 to 191, it's a Class B network. If the first number is from 192 to 223, it's a Class C network. Numbers above 223 are reserved for other purposes. The smaller the netid, the fewer number of networks that can b!

e subnetted, but the larger number of hosts on the network. A Class A rating is best for large networks while a Class C is best for small ones.

To create a subnet, the demarcation line on the IP address is moved between the netid and the hostid, to give the netid more bits to work with and to take away bits from the hostid. To do this, a special number called a subnet mask is used.

Subnetting is used when intranets grow over a certain size and they begin to have problems. One problem is management of host IP addresses-making sure that every computer on the network has a proper, up-to-date host address, and that old host addresses are put out of use until needed in the future. In a corporation spread out over several locations-or across the world-it's difficult, if not impossible, to have one person responsible for managing the host addresses at every location and department in the company.

Another problem has to do with a variety of hardware limitations of networks. Dissimilar networks may all be part of an intranet. An intranet may have some sections that are Ethernet, other sections that are Token Ring networks, and conceivably other sections that use different networking technologies altogether. There is no easy way for an intranet router to link these dissimilar networks together and route the information to the proper places.

Another set of problems has to do with the physical limitations of network technology. In some kinds of networks, there are some strict limitations on how far cables can extend in the network. In other words, you can't go over a certain distance of cabling without using repeaters or routers. A "thick" Ethernet cable, for example, can only be extended to 500 meters, while a "thin" Ethernet cable can only go to 300 meters. Routers can be used to link these cables together, so that an intranet can be extended well beyond those distances. But when that is done, each length of wire is essentially considered its own subnetwork.

Yet one more set of problems has to do with the volume of traffic that travels across an intranet. Often in a corporation, in a given department, most of the traffic is intradepartmental traffic-in other words, mail and other data that people within a department send to each another. The volume of traffic outside to other departments is considerably less. What's called for is a way to confine intradepartmental traffic inside the departments, to cut down on the amount of data that needs to be routed and managed across the entire intranet.

Subnetting solves all these problems and more. When an intranet is divided into subnets, one central administrator doesn't have to manage every aspect of the entire intranet. Instead, each subnet can take care of its own administration. That means smaller organizations within the larger organization can take care of problems such as address management and a variety of troubleshooting chores. If an intranet is subnetted by divisions or departments, it means that each division or department can guide the development of its own network, while adhering to general intranet architecture. Doing this allows departments or divisions more freedom to use technology to pursue their business goals.

Subnets also get around problems that arise when an intranet has within it different kinds of network architecture, such as Ethernet and Token Ring technologies. Normally-if there is no subnetting-a router can't link these different networks together because they don't have their own addresses. However, if each of the different networks is its own subnet-and so has its own network address-routers can then link them together and properly route intranet traffic.

Subnetting can also cut down on the traffic traveling across the intranet and its routers. Since much network traffic may be confined within departments, having each department be its own subnet means that all that traffic need never cross an intranet router and cross the intranet-it will stay within its own subnet.

Subnetting can also increase the security on an intranet. If the payroll department, for example, were on its own subnet, then much of its traffic would not have to travel across an intranet. Having its data traveling across the intranet could mean that someone could conceivably hack into the data to read it. Confining the data to its own subnet makes that much less likely to happen.

Dividing an intranet into subnets can also make the entire intranet more stable. If an intranet is divided in this way, then if one subnet goes down or is often unstable, it won't affect the rest of the intranet.

This all may sound rather confusing. To see how it's done, let's take a look at a network, and see how to use the IP address to create subnets. Let's say we have a Class B network. That network is assigned the address of When a network is given an address, it is assigned the netid numbers-in this case, the 130.97-and it can assign the host numbers (in this case, 0.0) in any way that it chooses.

The network is a single intranet. It's getting too large to manage, though, and we've decided to divide it into two subnets. What we do is fairly straightforward. We take a number from the hostid field and use it to identify each of the subnets. So one subnet gets the address, and the other gets the address Individual machines on the first subnet get addresses of,, and so on. Individual machines on the second subnet get addresses of, and so on.

Sounds simple. But we have a problem. The Internet doesn't recognize and as separate networks. It treats them both as since the "1" and "2" that we're using as a netid is only known to the Internet as a hostid. So our intranet router will not be able to route incoming traffic to the proper network.

To solve the problem, a subnet mask is used. A subnet mask is a 32-bit number in IP form used by intranet routers and hosts that will help routers understand how to route information to the proper subnet. To the outside Internet, there is still only one network, but the subnet mask allows routers inside the intranet to send traffic to the proper host.

A subnet mask is a number such as (the built-in default for Class C addresses; the Class B default is and the default for Class A is A router takes the subnet mask and applies that number against the IP number of incoming mail to the network by using it to perform a calculation. Based on the resulting IP number, it will route mail to the proper subnet, and then to a particular computer on the subnet. For consistency, everyone in a particular intranet will use the same subnet mask.

Subnetting an Intranet

When intranets are over a certain size, or are spread over several geographical locations, it becomes difficult to manage them as a single network. To solve the problem, the single intranet can be subdivided into several subnets, subsections of an intranet that make them easier to manage. To the outside world, the intranet still looks as if it's a single network.

  1. If you're building an intranet and want it to be connected to the Internet, you'll need a unique IP address for your intranet network, which the InterNIC Registration Services will handle. There are three classes of intranet you can have: Class A, Class B, or Class C. Generally, a Class A rating is best for the largest networks, while a Class C is best for the smallest. A Class A network can be composed of 127 networks, and a total of 16,777,214 nodes on the network. A Class B network can be composed of 16,383 networks, and a total of 65,534 nodes. A Class C network can be composed of 2,097,151 networks, and 254 nodes.

  2. When an intranet is assigned an address, it is assigned the first two IP numbers of the Internet numeric address (called the netid field) and the remaining two numbers (called the hostid field) are left blank, so that the intranet itself can assign them, such as The hostid field consists of a number for a subnet and a host number.

  3. When an intranet is connected to the Internet, a router handles the job of sending packets into the intranet from the Internet. In our example, all incoming mail and data comes to a router for a network with the netid of

  4. When intranets grow-for example, if there is a department located in another building, city, or country-there needs to be some way to manage network traffic. It may be impractical and physically impossible to route all the data necessary among many different computers spread across a building or the world. A second network-called a subnetwork or subnet-needs to be created.

  5. In order to have a router handle all incoming traffic for a subnetted intranet, the first byte of the hostid field is used. The bits that are used to distinguish among subnets are called subnet numbers. In our example, there are two subnets on the intranet. To the outside world, there appears to be only one network.

  6. Each computer on each subnet gets its own IP address, as in a normal intranet. The combination of the netid field, the subnet number, and then finally a host number, forms the IP address.

  7. The router must be informed that the hostid field in subnets must be treated differently than non-subnetted hostid fields, otherwise it won't be able to properly route data. In order to do this, a subnet mask is used. A subnet mask is a 32-bit number such as that is used in concert with the numbers in the hostid field. When a calculation is performed using the subnet mask and the IP address, the router knows where to route the mail. The subnet mask is put in people's network configuration files.

Overview of an Intranet Security System

Any intranet is vulnerable to attack by people intent on destruction or on stealing corporate data. The open nature of the Internet and TCP/IP protocols expose a corporation to attack. Intranets require a variety of security measures, including hardware and software combinations that provide control of traffic; encryption and passwords to validate users; and software tools to prevent and cure viruses, block objectionable sites, and monitor traffic.

  • The generic term for a line of defense against intruders is a firewall. A firewall is a hardware/software combination that controls the type of services allowed to or from the intranet.

  • Proxy servers are another common tool used in building a firewall. A proxy server allows system administrators to track all traffic coming in and out of an intranet.

  • A bastion server firewall is configured to withstand and prevent unauthorized access or services. It is typically segmented from the rest of the intranet in its own subnet or perimeter network. In this way, if the server is broken into, the rest of the intranet won't be compromised.

  • Server-based virus-checking software can check every file coming into the intranet to make sure that it's virus-free.

  • Authentication systems are an important part of any intranet security scheme. Authentication systems are used to ensure that anyone trying to log into the intranet or any of its resources is the person they claim to be. Authentication systems typically use user names, passwords, and encryption systems.

  • Server-based site-blocking software can bar people on an intranet from getting objectionable material. Monitoring software tracks where people have gone and what services they have used, such as HTTP for Web access.

  • One way of ensuring that the wrong people or erroneous data can't get into the intranet is to use a filtering router. This is a special kind of router that examines the IP address and header information in every packet coming into the network, and allows in only those packets that have addresses or other data, like e-mail, that the system administrator has decided should be allowed into the intranet.

All intranets are vulnerable to attack. Their underlying TCP/IP architecture is identical to that of the Internet. Since the Internet was built for maximum openness and communication, there are countless techniques that can be used to attack intranets. Attacks can involve the theft of vital company information and even cash. Attacks can destroy or deny a company's computing resources and services. Attackers can break in or pose as a company employee to use the company's intranet resources.

Firewalls are hardware and software combinations that block intruders from access to an intranet while still allowing people on the intranet to access the resources of the Internet. Depending on how secure a site needs to be, and on how much time, money, and resources can be spent on a firewall, there are many kinds that can be built. Most of them, though, are built using only a few elements. Servers and routers are the primary components of firewalls.

Most firewalls use some kind of packet filtering. In packet filtering, a screening router or filtering router looks at every packet of data traveling between an intranet and the Internet.

Proxy servers on an intranet are used when someone from the intranet wants to access a server on the Internet. A request from the user's computer is sent to the proxy server instead of directly to the Internet. The proxy server contacts the server on the Internet, receives the information from the Internet, and then sends the information to the requester on the intranet. By acting as a go-between like this, proxy servers can filter traffic and maintain security as well as log all traffic between the Internet and the network.

Bastion hosts are heavily fortified servers that handle all incoming requests from the Internet, such as FTP requests. A single bastion host handling incoming requests makes it easier to maintain security and track attacks. In the event of a break in, only that single host has been compromised, instead of the entire network. In some firewalls, multiple bastion hosts can be used, one for each different kind of intranet service request.

How Firewalls Work

Firewalls protect intranets from any attacks launched against them from the Internet. They are designed to protect an intranet from unauthorized access to corporate information, and damaging or denying computer resources and services. They are also designed to stop people on the intranet from accessing Internet services that can be dangerous, such as FTP.

  1. Intranet computers are allowed access to the Internet only after passing through a firewall. Requests have to pass through an internal screening router, also called an internal filtering routeror choke router. This router prevents packet traffic from being sniffed remotely. A choke router examines all pack-ets for information such as the source and destination of the packet.

  2. The router compares the information it finds to rules in a filtering table, and passes or drops the packets based on those rules. For example, some services, such as rlogin, may not be allowed to run. The router also might not allow any packets to be sent to specific suspicious Internet locations. A router can also block every packet traveling between the Internet and the internal network, except for e-mail. System administrators set the rules for determining which packets to allow in and which to block.

  3. When an intranet is protected by a firewall, the usual internal intranet services are available-such as e-mail, access to corporate databases and Web services, and the use of groupware.

  4. Screened subnet firewalls have one more way to protect the intranet-an exterior screening router, also called an exterior filtering router or an access router. This router screens packets between the Internet and the perimeter network using the same kind of technology that the interior screening router uses. It can screen packets based on the same rules that apply to the internal screening router and can protect the network even if the internal router fails. It also, however, may have additional rules for screening packets specifically designed to protect the bastion host.

  5. As a way to further protect an intranet from attack, the bastion host is placed in a perimeter network-a subnet-inside the firewall. If the bastion host was on the intranet instead of a perimeter network and was broken into, the intruder could gain access to the intranet.

  6. A bastion host is the main point of contact for connections coming in from the Internet for all services such as e-mail, FTP access, and any other data and requests. The bastion host services all those requests-people on the intranet contact only this one server, and they don't directly contact any other intranet servers. In this way, intranet servers are protected from attack.

Pawan Bangar, technical Director, Birbals, India.


Data Recovery Software and Undelete from R-TT
Disk management software including utilities for data recovery, drive imaging, disk wiping and access control.
Data Recovery | Email Data Recovery by Ontrack
Data recovery services, data recovery software, file repair software, and diagnostic software from Ontrack. Software for email recovery, file recovery and ...
Data Recovery by DriveSavers | Hard Drive Data Recovery
Worldwide data recovery service for all operating systems and storage media. Authorized by all drive manufacturers.
Hard Drive Data Recovery Software Tools, Disk Recovery Utilities ...
Offers data recovery software,data recovery services for hard drive recovery and data safety software services for your computer. Buy award winning data ...
Data Recovery by FADV – Hard Drive, RAID, Tape, Database and more ...
Offers data recovery services for all hard drive models. RAID, MS SQL, Exchange, Tapes, Camera and USB media, CD and DVD. Service available 24/7.
Data Recovery Software - File System Utilities
Data recovery software for all Windows file systems. Recover deleted files, corrupted hard drives, and partitions.
Professional Data Recovery Software from Bitmart. File Recovery ...
Data Recovery Software Restorer2000. Undelete & File Recovery utility for FAT and NTFS file systems. Data Recovery from damaged disks and partitions.
Data Recovery Services - ActionFront - Critical Server Data Recovery
ISO certified data recovery services with labs in Atlanta, Santa Clara, Dallas, Chicago, Toronto (also Buffalo and Tokyo Japan)
Hard Drive Data Recovery Software: Recover Deleted Files- Recover ...
Data recovery software for recovering files that have been deleted or lost due to the hard drive format, virus infection, unexpected system shutdown or ...
Data Recovery Group - Hard Drive Data Recovery Services
Data Recovery is Our Only Business! Data Recovery Group's a complete data recovery service that specializes in recovering data from hard disk drives.
Data Recovery by CBL: Hard Drive Recovery Services
Worldwide Data Recovery Services at CBL. Specializing in data recovery, hard drive recovery, hard disk drive recovery and RAID data recovery.
Data Recovery Software, File Repair Utilities, Hard Disk Recovery ...
Hard drive data recovery software to perform data recovery & recover deleted files from Novell, Linux, Unix, Mac, Windows & data recovery services for hard ...
AT&DR: Data Recovery and Liabillity
Associated Technologies offers complete data recovery solutions with services for any type of data storage device, including the following: hard drives, ...
Ontrack UK - Data recovery services & recovery software - hard ...
Ontrack offers data recovery services & software for: hard drive recovery, file recovery, server recovery, email recovery, tape recovery, RAID recovery.
Beginners Guides: Hard Drive Data Recovery -
Beginners Guides: Hard Drive Data Recovery -
File Recovery and Data Recovery Software. Hard Drive recovery utility
Data recovery software for FAT, NTFS, Ext2FS file systems. File recovery after FDISK, MBR destruction, FAT damaged, virus infection. Dynamic disk support.
Data recovery - Wikipedia, the free encyclopedia
Data recovery is the process of salvaging data from damaged, failed, ... Although there is some confusion as to the term, data recovery can also be the ...
Active@ UNDELETE Data Recovery. Recover Deleted Files. Windows XP ...
Active@ UNDELETE - Data Recovery Software for all Windows File Systems. Recover deleted files from lost, damaged, formatted or reformatted partitions.
New Zealand Data Recovery & Computer Forensics Experts
New Zealand data recovery specialists & computer forensics investigation experts. Recovering lost data for businesses or legal evidence is all we do.
Canada Data Recovery Services: Hard Disk Drive Recovery, Raid Data ...
Provides data recovery solutions for companies experiencing data loss from failed hard drives, raid arrays, and server systems.


Content Menu
  • 10 easy steps to speed up your computer without upgrading

  • 10 proven tips to survive a computer crash

  • 7 critical steps to protect your data

  • add value by documenting your business

  • an introduction to tape backup

  • an outsourcers passage to india how to do it part i

  • are you prepared for a hard drive crash

  • asset searching for recovery actions the decision makers critical tool part 2

  • asset searching for recovery actions the decision makers most critical tool part 1

  • a beginner guide to web hosting

  • a customer complaint management system

  • a fresh start for family finances in 2005

  • background of password cracking

  • backing up your stuff part 2 a solution

  • before you take the plunge essential information on data recovery

  • booting problem in pc

  • business continuity and disaster recovery a business not a technology issue

  • business continuity and disaster recovery business impact analysis

  • business continuity and disaster recovery reducing your risk profile

  • business continuity and disaster recovery risk analysis and control

  • business continuity and disaster recovery selecting a business continuity strategy

  • business continuity and disaster recovery the business continuity and disaster recovery plan

  • business continuity testing starts with the risks

  • business needs vs network performance critical challenges facing network managers

  • can raid systems fail

  • career paths for a comptia a certified technician

  • career paths for comptia a certified technician

  • choosing a data recovery company

  • choosing data recovery company

  • common problems why hard disks crash

  • comparing data recovery software

  • compensating for disruptions in the oil and gas industry

  • computer data recovery options

  • computer disposal throwing away your computer money and idenity

  • computer viruses the basics

  • coping with a serious data loss from your computer hard drive

  • corporate information security is our information more secure since september 11th

  • datarecoverynet com enters medical industry

  • data backups are the biggest security threats

  • data backups are the biggest security threats surprised

  • data backups one key to business survival

  • data recovery

  • data recovery 1 on 1

  • data recovery and data loss a costly proposition

  • data recovery and data safety tips

  • data recovery beginners tips

  • data recovery for less

  • data recovery from laptops

  • data recovery made easy

  • data recovery software at your rescue

  • data recovery software comparison

  • data recovery the best method is prevention

  • data recovery the easy way

  • data recovery what not to do

  • data recovery what you need

  • data recovery you can get it back

  • data security are your assets secure

  • dealing with your pending pc disaster a guide for small business

  • did you ever want to completely erase everything on your computer

  • dirty little computer viruses and how to protect yourself

  • disaster planning ­v how important is it to you

  • disaster preparedness in a post 9 11 world

  • disaster recovery more than meets the eye

  • disc and data recovery

  • document management features for 2003

  • does it worth to backup emails from clients like outlook express

  • do it yourself data recovery freezer method

  • do i really need to backup

  • drive solutions inc expands data recovery service

  • easy file recovery basic backup guidelines

  • easy guide to raid recovery

  • eliminating the risk of delivering network ready applications

  • email recovery good software can fix your lost mail trouble

  • esecurity

  • exchange disaster recovery with sanrad v switch planning guide

  • e commerce a no nonsense perspective for new business

  • flash usb drive backup easily conveniently and securely

  • focusstor launches a new data backup recovery software

  • getting more bang for the storage buck

  • get down with ocp evaluating dba job applicants in an ocp world

  • got virus

  • got virus your data is not lost forever

  • great plains accounting support overview for it specialist

  • great plains dos support notes for consultant

  • great site ranking in google the secrets out

  • hackers given access to irs computers

  • hard disk data recovery expert choosing yours

  • hard dive failure what is a head crash

  • hard drive crash avoid making a bad situation worse

  • hard drive crash the essential data recovery report

  • health and medical advice on the internet use it wisely to overcome illness and find more happiness in your life

  • highlights of irs list of 2005 tax scam

  • highlights of irs list of 2005 tax scams

  • how multiple server hosting impacts your websites uptime

  • how multiple server hosting impacts your website s uptime

  • how multiple server hosting impacts your web sites uptime

  • how safe is your success part 5 of 8

  • how safe is your success part 6 of 8

  • how secure are online data backups

  • how to avoid everyday sales mistakes

  • how to backup a pc

  • how to backup windows xp home edition

  • how to backup your computer files

  • how to backup your hard drive

  • how to check the status of your tax refund online

  • how to fight cyberterrorism

  • how to prevent computer security risk and how to keep your small business safe

  • how why gps offers affordable fleet tracking

  • how you can avoid my data recovery nightmare

  • hr managers use computer forensics to investigate employee allegations

  • hurricanes wilma katrina and rita force businesses to rethink computer

  • identity theft and credit reports

  • identity theft recovery the road back

  • identity theft safeguarding cant hurt

  • identity theft the road back

  • improving sql performance

  • index

  • information security for smes

  • insure your information backup software

  • internet network security policies need a radical rethink

  • intranet

  • iscsi vs fc for meeting mission critical requirements

  • its all in the planning disaster recovery

  • it department skills to support microsoft great plains and microsoft crm

  • it in house support microsoft great plains and crm

  • keep a diary of your computer

  • learn how to safely backup your hard drive

  • lightning season how to avoid data loss

  • linux or windows which is it

  • loans for bad debtors discarding debt disorganization to recover financial growth

  • local vs remote data backup the pros and cons

  • mcse 70 290 certification primer

  • microsoft great plains customization recovery upgrade for large corporation

  • microsoft great plains customization upgrade recovery visual studio vb 6 0

  • microsoft r exchange server utilities eseutil isinteg

  • microsoft sql 2000 disaster recovery with sanrad v switch planning guide

  • mr

  • need a copy of your tax return information

  • new generation of financial information systems makes crunching numbers faster and easier

  • new iomega tera series desktop hard drive with 1tb capacity

  • nucleus kernel for fat and ntfs

  • nucleus kernel for fat data recovery software

  • nucleus kernel for fat ntfs data recovery software

  • nucleus kernel for ntfs data recovery softwares

  • online investing and trading discussions at www streetplayer com

  • openly sharing your rfp objectives and information with vendors

  • options for computer data recovery

  • outsourcing it asset retirement

  • outsourcing multiplying it services

  • paragon drive copy 8 0

  • planning for 2002 business recovery use public relations firepower

  • protecting your identity on the internet

  • protect yourself before your hard drive crashes

  • quick system restore with asr backups

  • raid disk recovery

  • ready for a business recovery

  • recognizing a pc with malware

  • recover deleted data easily

  • reduce tco the java database way

  • reinstall windows xp on your computer

  • rotator

  • scalability testing 7 steps towards success

  • scalability testing 7 tips for improvement

  • secure offsite backup services and software online file backup and storage remote online backup

  • secure your data windows data backup computer software

  • small business computer security the basics

  • small business network security 101

  • software that takes care of other software

  • sql administrator skills required to support microsoft great plains

  • syi save your identity

  • teosoft cleanspace 9 software

  • the best data recovery choice for you

  • the day my laptop was stolen almost killed my business

  • the devastation of data loss and what you can do about it

  • the essential data recovery report

  • the google patent reveals the secret to great site ranking

  • the importance of engaging a qualified data recovery expert

  • the importance of proper security for your pc

  • the mystery of the unknown

  • the seven deadly habits of a dba and how to cure them

  • the seven golden rules of data backups

  • the worst case scenario how to protect your data

  • think you have a dead hard drive

  • top 10 ways to protect yourself from computer viruses

  • top 10 ways to protect yourself from online identity theft

  • top 5 backup tools you can pick up for pennies

  • top 7 reasons you should back up your data online

  • top computer problems leading to data recovery

  • trouble shooting hard drive problems part 2

  • using sanrad v switch as the vss hardware provider for windows backups

  • using system restore to save yourself from formatting your hard drive

  • webfarms ii balancing the load

  • welcome to the world of knoppix

  • what could macedonia learn from a tiger the asian tigers and the phenomenon of uninterrupted economic growth

  • what is data recovery

  • what is data recovery a brief introduction

  • why usability is important to you

  • will you recover

  • working from home for yourself or someone else

  • your hard disk failed dont panic

  • your hard disk failed don t panic

  • your hard drive is going to explode why a ups is essential

  • your privacy exposed computer forensics international uncovers secrets about recycled hard drives

  • you can recover deleted data

  • you lost your data dont panic

  • you need to backup