Do you know about - Intranet
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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 generally understood idea. Naturally put, an intranet is a secret network with Internet technology used as the fundamental 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 fundamental 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 varied databases, are being integrated into an intranet. A wide range of tools allow this to happen. Base Gateway Interface (Cgi) scripting is often used to passage heritage databases from an intranet. The Java programming language can be used to passage heritage databases as well.
With the large increase of the Internet, an expanding number of people in corporations use the Internet for communicating with the exterior world, for convention 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 significant internally and that is why intranets are becoming so popular. Some corporations do not have Tcp/Ip networks, the protocol required to passage 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 passage 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 secret network instead of to a social Internet provider. Interoperability between networks is an additional one large bonus.
Security systems isolate an intranet from the Internet. A company's intranet is protected by firewalls-hardware and software combinations that allow only positive people to passage the intranet for specific purposes.
Intranets can be used for anyone that existing networks are used for-and more. The ease of publishing information on the World Wide Web has made them beloved 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 literally and more effectively. Software known as groupware is an additional one important part of intranets. It allows people to collaborate on projects; to share information; to do videoconferencing; and to make procure procedures for yield work. Free server and client software and the multitude of services, like newsgroups, stimulated the Internet's growth. The consequence of that increase stimulated and fueled the increase of intranets. The ease with which information can be shared, and with which people can spin with one an additional one will continue to drive the building of intranets.
A Global View of an Intranet
An intranet is a secret corporate or educational network that uses the Internet's Tcp/Ip protocols for its fundamental transport. The protocols can run on a range 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 passage from the Internet.
Videoconferencing is an important application that requires sending gigantic quantities of data. Intranets can be built using components that allow the very high bandwidths required for transferring such information. Often an intranet is composed of a number of different networks inside a corporation that all spin with one an additional one via Tcp/Ip. These isolate networks are often referred to as subnets. Software that allows people to spin with each other via e-mail and social message boards and to collaborate on work using workgroup software is among the most considerable 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 associates to do business-to-business transactions, such as ordering parts, sending invoices, and production payments. For extra security, these intranet-to-intranet transactions need never go out over the social Internet, but can trip over secret leased lines instead. Intranets are a considerable principles for allowing a company to do company online, for example, to allow anyone on the Internet to order products. When man orders a product on the Internet, information is sent in a procure manner from the social 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 composition 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 associate to "legacy systems"-hardware and databases that were built before an intranet was constructed. heritage systems often use older technology not based on the intranet's Tpc/Ip protocols. There are a range of ways in which intranets can tie to heritage systems. A Base way is to use Cgi scripts to passage the database information and pour that data into Html formatted text, production it ready to a Web browser. Information sent across an intranet is sent to the proper destination by routers, which observe 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 straight through any other routers. If it is to be sent to an additional one subnetwork on the intranet, it will be sent to an additional one internal router address. If the packet is to be sent to a destination exterior 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 secret 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 straight through a series of switches called routers. Once all the packets arrive at their destination, they are recombined into their former 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.
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 converyance mechanism for Ipx packets. 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 literal, number of data in the packet. Each packet, along with the checksum, is put into isolate Ip wrappers or "envelopes." These wrappers comprise 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. The packets trip between networks by intranet routers. Routers observe all Ip wrappers and look at their addresses. These routers determine the most effective 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 settled inside the intranet, the packet may be sent directly to its destination, or it may instead be sent to an additional one router. If the address is settled out on the Internet, it will be sent to an additional one router so it can be sent across the Internet. 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 while transmission. It then discards the packet and asks that the former packet be retransmitted. Tcp includes the quality 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. 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 former 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 buildings exists at the corporeal 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 arrival means that a range 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 Naturally 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 implicated with any of the other layers. The session layer allows for the transportation 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 salvage a file. If something prevents it from completing the save, the session layer, which has a narrative of the former state, returns to the former state rather than allowing a corrupt or incomplete transaction to occur. The converyance layer segments the data into standard 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 significant for literal, 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 part of the Mac sublayer of the Ieee 802.2, 802.3 and other standards. Ethernet and Token Ring are the two most Base corporeal layer protocols. They function at the Mac (Media passage Control) level and move the data over the cables based on the corporeal address on each Nic (Network Interface Card). The corporeal layer includes the corporeal components of the Ieee 802.3 and other specifications.
How Tcp/Ip Packets Are Processed
Protocols such as Tcp/Ip determine how computers spin with each other over networks such as the Internet. These protocols work in concert with each other, and are layered on top of one an additional one in what is generally referred to as a protocol stack. Each layer of the protocol is designed to perform 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 converyance 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 converyance 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 while 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 former 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 distance 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 former datagram. It strips off the Ip header, and then sends the datagram to the converyance layer. The converyance layer looks at the remaining header to determine 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 straight 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 straight 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 corporeal network layer, which specifies the corporeal 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 corporeal 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 associate different parts of a single network, such as different sections of an intranet. They associate 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 associate an entire subnetwork to an entire subnetwork. To do that, more sophisticated pieces of technology called routers are used.
When there is a great number 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. 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 group Lan, and so it needn't trip straight 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 trip across bridges is traffic bound for an additional one Lan. Any traffic within the Lan need not trip across a bridge. 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 fundamental 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 Bridges consult a studying 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 an additional one Lan, it forwards the packet. The bridge constantly updates the studying table as it monitors and routes traffic. Bridges can associate Lans in a range of different ways. They can associate Lans using serial connections over former phone lines and modems, over Isdn lines, and over direct cable connections. Csu/Dsu units are used to associate bridges to telephone lines for remote connectivity. 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 an additional one 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 an additional one 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 composition of hardware and software-can send the data to a computer on the same sub network inside the intranet, to an additional one network on the intranet, or exterior 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.
A router has input ports for receiving Ip packets, and yield 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 varied destinations. Based on the information in the routing table, the packet is sent to a single yield port, which sends the packet to the next closest router to the packet's destination. If packets come to the input port more swiftly than the router can process them, they are sent to a retention 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 distance 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. In a easy intranet that is a single, fully 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 easy with very few entries, and is constructed automatically by a schedule called ifconfig. In a slightly more involved intranet which is composed of a number of Tcp/Ip-based networks, and connects to a minute 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 turn routes as network traffic changes, and so isn't convenient for many intranets. In more involved intranets, dynamic routing will be required. Dynamic routing is used to permit complicated routes for a packet to reach its final destination. Dynamic routing also allows routers to turn the way they route information based on the number 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 turn agreeing to network traffic and conditions. 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 Base interior routing protocol is the Routing information Protocol (Rip). exterior protocols are typically used for external routers on the Internet. AÊcommon 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 comprise dozens or hundreds of computers. And in a large corporation, there may be thousands of computers spread across the globe, all linked 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, agreeing 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 easy 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 be 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 extra number called a subnet mask is used.
Subnetting is used when intranets grow over a positive size and they begin to have problems. One question is administration of host Ip addresses-making sure that every computer on the network has a proper, new 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 man responsible for managing the host addresses at every location and group in the company.
Another question has to do with a range of hardware limitations of networks. different 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 different networks together and route the information to the proper places.
Another set of problems has to do with the corporeal limitations of network technology. In some kinds of networks, there are some literal, limitations on how far cables can enlarge in the network. In other words, you can't go over a positive 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 distance 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 group send to each another. The volume of traffic exterior 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 number 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 carry on 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 administration and a range of troubleshooting chores. If an intranet is subnetted by divisions or departments, it means that each group or group can guide the improvement of its own network, while adhering to general intranet architecture. Doing this allows departments or divisions more freedom to use technology to pursue their company 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 group 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 trip across an intranet. Having its data traveling across the intranet could mean that man 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 work on 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 130.97.0.0. 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 130.97.0.0 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 recognize each of the subnets. So one subnet gets the address 130.97.1.0, and the other gets the address 130.97.2.0. individual machines on the first subnet get addresses of 130.97.1.1, 130.97.1.2, and so on. individual machines on the second subnet get addresses of 130.97.2.1, 130.97.2.2 and so on.
Sounds simple. But we have a problem. The Internet doesn't recognize 130.97.1.0 and 130.97.2.0 as isolate networks. It treats them both as 130.97.0.0 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 exterior 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 255.255.255.0 (the built-in default for Class C addresses; the Class B default is 255.255.0.0 and the default for Class A is 255.0.0.0). 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 single computer on the subnet. For consistency, everybody in a single intranet will use the same subnet mask.
Subnetting an Intranet
When intranets are over a positive size, or are spread over several geographical locations, it becomes difficult to carry on 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 exterior world, the intranet still looks as if it's a single network.
If you're building an intranet and want it to be linked 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. 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 147.106.0.0. The hostid field consists of a number for a subnet and a host number. When an intranet is linked 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 147.106.0.0. When intranets grow-for example, if there is a group settled in an additional one building, city, or country-there needs to be some way to carry on network traffic. It may be impractical and physically impossible to route all the data significant among many different computers spread across a building or the world. A second network-called a subnetwork or subnet-needs to be created. In order to have a router cope 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 exterior world, there appears to be only one network. Each computer on each subnet gets its own Ip address, as in a general intranet. The composition of the netid field, the subnet number, and then ultimately a host number, forms the Ip address. 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 255.255.0.0 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 wish a range of security measures, including hardware and software combinations that supply 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 composition that controls the type of services allowed to or from the intranet. Proxy servers are an additional one Base tool used in building a firewall. A proxy server allows principles administrators to track all traffic coming in and out of an intranet. A bastion server firewall is configured to withstand and prevent unauthorized passage 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 man 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 extra 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 principles administrator has decided should be allowed into the intranet.
All intranets are vulnerable to attack. Their fundamental Tcp/Ip architecture is same 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 passage to an intranet while still allowing people on the intranet to passage the resources of the Internet. Depending on how procure 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 former 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 man from the intranet wants to passage 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 speak security as well as log all traffic between the Internet and the network.
Bastion hosts are heavily fortified servers that cope all incoming requests from the Internet, such as Ftp requests. A single bastion host handling incoming requests makes it easier to speak 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, complicated 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 passage 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.
Intranet computers are allowed passage to the Internet only after passing straight through a firewall. Requests have to pass straight 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. 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. principles administrators set the rules for determining which packets to allow in and which to block. When an intranet is protected by a firewall, the usual internal intranet services are available-such as e-mail, passage to corporate databases and Web services, and the use of groupware. Screened subnet firewalls have one more way to protect the intranet-an exterior screening router, also called an exterior filtering router or an passage 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 added rules for screening packets specifically designed to protect the bastion host. As a way to added protect an intranet from attack, the bastion host is settled 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 passage to the intranet. A bastion host is the main point of touch 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 touch only this one server, and they don't directly touch any other intranet servers. In this way, intranet servers are protected from attack.
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