냐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� +-+-+-+-+-+-+-+-+ 栢栢栢栢昉께께굇굇굅같�|O|u|t|b|r|e|a|k|臍같굇굇굉께께栢栢栢� +-+-+-+-+-+-+-+-+ Issue #2 - Page 7 of 12 냐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� Greetings to all, and shout outs to #hackerzlair And the crew at Outbreak Magazine. TCP/IP part I -------------- By: antimatt3r (aka: xD0Sx, Tim) Introduction: TCP/IP remains a hot topic these days, because it is, was, and always will be the glue that holds the Internet and World Wide Web together. In order to be well-connected, network wise that is, sooner or later you have to become familiar with TCP/IP. So if you want to understand what it is, what it does, what its for, why you need it, and what you do with it, but you just don't know where to start - this text is for you. This IS NOT a formal tutorial, skip around a bit and read as much or as little as you want. If you feel the need to impress colleagues and even your boss, gather enough information to throw them around a bit at meetings and cocktail parties. On the other hand, you can go as far as discovering the most important features and tools, as well as the role that TCP/IP plays in the Internet. It's all right here on your screen. So now, we begin getting in to the technicities of this wonderful protocol. TCP/IP Stands for Transmission Control Protocol / Internet Protocol A protocol is a set of rules for behavior that people accept and obey. Sometimes the rules are written down, the rules for driving for example. Still they vary from country to country and region to region. In the United States, a yellow light means, prepare to stop, the light is going to turn red. But in Germany, a yellow light means, get ready, the light is going to turn green. Similarly, two or more computers need rules for behavior. Common behaviors regarding the connection are not enough. There also has to be a common language. To communicate, the computers need to `speak' the same language, and the one they use most often is TCP/IP. So in the world of computers, a protocol is the collection of designated practices, policies, and procedures - often unwritten but agreed upon by the users - and the language that facilitates electronic communication. If networks are the basis of the Information Superhighway, the TCP/IP protocols are the rules of the road. TCP/IP is often referred to as the protocol of open systems. Here is the world's shortest definition of open systems. Open systems provide a standards-based computing environment. The term "open systems" is kind of a computer industry buzzword. Many of the concepts of open systems began with the UNIX operating system. Even though UNIX runs of dozens of different computers, most of the commands are the same on every computer. So although TCP/IP sounds like just one or two protocols, it is actually a whole set of protocols for connecting computers into the Internet. This set of protocol is called the TCP/IP stack. You may be used to thinking of a transport as the way you move yourself or your things around. But computer networks move information from one place to another. Many times you don't care exactly how the data gets where it needs to go as long as it arrives on time, affordably, intact and uncorrupted. TCP/IP is both a transport for carrying your data and a protocol with rules for how your data should move. And there is one more piece: TCP/IP also has a set or applications, or programs, for chatting with other people on a network, for moving files, for signing on to other computers, and more. TCP/IP ties networks and the Internet together, regardless of the hardware and software used to build those networks. TCP/IP runs on and connects just about everything. You may have heard about other network protocols such as IBM's SNA or Novell SPX/IPX. But no protocol connects as many different hardware and software platforms as TCP/IP. This versatility is the reason that TCP/IP is the worlds' most popular network protocol. From the beginning, TCP/IP was designed to link computers from different vendors such as IBM and Hewlett Packard, to name just two. Other network protocols are no where near this flexible. With TCP/IP, you can buy the computer you want or need and know that it can communicate with all of the others. Because all implementations of TCP/IP must work together, or interoperate, regardless of who created them, you may have several implementations from which to choose. The various products may differ in price, number of features, performance, or in any number of other ways. Investigate your options carefully and make the right choice for your circumstances. The widespread incorporation of TCP/IP is one indication of its popularity. Other vendors' TCP/IP implementations are still important, though, because they may have features that the bundled implementations don't have. Computer networking is rapidly becoming a part of life - not just at work, but as home as well. Networks are a combination of hardware and software, and the TCP/IP protocols are the software that glues their hardware into a working network. So before you get into the software, I think you should understand some basic network concepts and terminology, as well as the relationship between networking hardware, and software. TCP/IP provides connectivity for networked computers. Because its hard to describe just the TCP/IP piece without introducing how the machines are organized and cabled together in a network, this part of the document describes just that. A network is described as being a combination of computers (and other devices) along with the cabling, the network interface controllers that are inside the device, and the network software. The protocol software governs how information gets transported on the network hardware, and TCP/IP is the more widely used protocol on the largest variety of hardware. So what kind of devices can be a part of a network you wonder? Any device that sends or receives information can be part of a network. Computers, PDAs, printers, cash registers, communication devices and lots of thing you might not expect to see on a network such as pop machines, toasters and toilets can be part of a network. With all those hardware possibilities to be placed on a network, you can see why you need rules for how data is transferred across the connection media among all those components. These rules are the network protocols, such as TCP/IP. Some of the other network protocols available are IPX from Novell and SNA from IBM as mentioned earlier. Networks and protocols are inseparable; without networks protocols have no reason to be around, and without protocols, networks would just be piles of expensive hardware that would be useless. It would be like driving without knowing what a car was. Impossible. A network provides many conveniences and services to its users. You can move information and files from one computer to another. Without copying them, you can access shared objects like directories and files on other computers. You can share printers attached to other computers, use applications that take advantage of the network, send e-mail to other people who are connected to the network, use Internet telephony software, participate in electronic discussion groups and learn new things by taking classes online, browsing the Internet or taking web-based seminars called webinars. To make recourse sharing useful and reliable, most organizations install computers that are dedicated wholly to sharing disks or printers with many other users. These computers are managed so they will always be available and are called file servers, print servers, or just servers. Protocols are not really tangible "things" on the network. Instead, they specify how tangible things communicate with each other. Each time a network device manipulates your data, it obeys the rules of TCP/IP. One rule stipulates that your data may have to be transferred in smaller pieces. TCP/IP makes sure your data does not get ruined in the process of getting put together again after an error. For example, King TCP/IP tells the network devices what to do with Humpty Dumpty's pieces. The data that you send and receive over the network is packaged into one or more packets. Each packet holds the data that it has to transmit, and control information, which tells the network what to do with the packets. The network protocol - in this case TCP/IP - determines the format for each packet. And all of this is transparent to the user. The difference between Humpty Dumpty and your messages is that your messages can be put back together, as for Humpty, he's scrambled. After the packets are sent, they may not arrive in order at their destination. When your data gets spread over many packets, TCP/IP governs how the packets are put back together after being split, transferred, and arriving at their destination. TCP/IP sequences packets correctly. To be continued in the next issue of Outbreak Magazine!