History of Internet:
In 1969, the American defense department wanted to connect all the computers in the Department of Defense (DOD) offices and military research contractors including a large number of universities doing military funded research. That network was called Advanced Research Projects Agency Network (ARPHANET), was also called DARPANET, the D for defense. It started in a small way, connecting three computers in California with one in Utah, but quickly grew to span the whole of America. It was very successful and all the universities wanted to get connected to ARPHNET. At one stage the military officials wanted to preserve the unity of DOD, and so divided the network into two parts:
ARPHANET
MILNET (Military Network)
These two parts remained connected with a technical scheme called Internet Protocol.
The American National Science Foundation then established another network of computers in America. It permitted all the universities and research centers to hook on to their network National Science Foundation Network (NSFNET) and to contribute to super-computer research. During 1990, many computers started hooking up to NSFNET. During 1994, several commercial organizations introduced networks across to another node in another network. As a result of this we now have a network of so many different networks. This network of networks is called the Internet.
Internet
A collection of computers all over the world that send, receive, and store information. It’s merely a lot of computers communicating with each other. Access to the Internet is provided through a number of sources: universities, government installations, the military, large companies, and individuals through Internet service providers.
Internet Service Provider:
A commercial organization that provides dial-up access to the Internet, like a cable company for computer users who want to get on the Internet. Often called ISPs, an Internet Service Provider is already connected to the Internet. They provide us with an access code and phone number, which we use to get to the Internet. Additionally, they should offer email accounts.
World Wide Web:
The world wide web is an architectural framework for accessing linked documents spread out over thousands of machines all over the Internet.
Web server:
A computer or software program that runs on a computer and answers requests for Web pages on the World Wide Web. Web servers are usually part of an Internet service provider’s array of computers. Or a business may have a computer that works as a web server answering HTTP requests from the Internet and sending Web page information to other computers.
URL:
Uniform Resource Locator, a type of command that can fetch a variety of types of information from various corners of the Internet. Common URLs are
http - for web pages
ftp - for file transfer protocol sites
gopher - for gopher servers
mailto - for sending e-mail
news - for accessing newsgroups
Web Browser:
Web browser software designed to view documents written in HTML, which includes all pages on the World Wide Web. There are two popular Web browsers: one from Netscape and the other from Microsoft. Web browsers displays information from the Internet by using text, graphics, sounds, and all sorts of interesting distractions. The browsers can also display Gopher, FTP, and newsgroup information.
- Netscape Navigator
- Mosaic
- Hot Java
File Transfer Protocal(FTP)
Introduction
In current times if you want to transfer a file to a friend, you can just attach it in an email and send it off. With high speed bandwidth being so cheap and plentiful to the home user, transferring a file in this manner is usually more than adequate. What if you needed to transfer the file to someone immediately; there could be no delays, it has to be fast, and the files you are transferring may be very large. In a scenario like this, email will most likely not be adequate. This is because most email providers limit the size of your mailbox on their servers, the size of attachments you may receive, and that there is no guarantee when you send email how long it will take for the recipient to receive it or if it will even get there. This is where FTP comes in.
FTP stands for the File transfer protocol and is used to transfer files between an FTP server and another computer. In the past, FTP was much more common than it is today and was the dominant file transfer mechanism on the Internet. If you needed to transfer files between two computers, you would use FTP to do so. FTP is still very popular today when a service requires that a lot of files be hosted for other to people to download. FTP also tends to be faster than other contemporary methods of transferring files because it was designed to do so.
Even more important, FTP support Automatic Resume. This means that if you are downloading the latest new game demo that is over 600 megs, and for some reason the download stops in the middle of the transfer, the ftp client will attempt to on the next download of the same file, to continue from where you left off. This feature can save you a huge amount of time but is generally only found in specialized FTP client software and not in your browser software.
How to Connect to an FTP Server
There are two approaches to allowing users to connect to an FTP Server. The first is to make it so anyone can log in anonymously, otherwise known as anonymous FTP, or you can assign user names and passwords to people that they must use to log in to the server.
The two most common ways to connect to an FTP server is with your Web Browser or with a FTP client such as FileZilla. To connect to a FTP server with your browser you would prefix the hostname you are connecting to with the ftp:// protocol statement. For example, ftp://www.bleepingcomputer.com. It would then try to connect anonymously. If the server you are trying to connect to requires a username and password, you can do so in the following format:
It is recommended when you do connect with a username and a password that you do not put the password in as well, otherwise it will show up in your browser's history. Instead do this:
This way your browser will prompt you for a password and you do not have to worry about it being stored in your history list, which can potentially be a security risk.
The other method is to use a FTP client that is designed specifically to connect to FTP servers. These types of software are generally the best as they have been streamlined for speed and support a lot of the advanced features like automatic resume. You should browse through the list of FTP Clients and find one you like.
How to Transfer Files
Whether you are connected to an FTP server via your web browser or an FTP client, you will be presented with a list of folders and documents that have files you can download to your computer. If you are using a web browser, you will click on the file you would like to download and it will prompt you to save it or open it. Unless you really know what it is you are downloading, you should save it to a directory that you will know how to find later, and open it from there.
If you are using an FTP Client, you will be presented a list of the files that you can download. You should first specify where you would like downloads to save to, and then you can double click on the file to start the download. When you are done downloading, you can shut the FTP client and open the file from where it was stored.
Internet Applications:
Electronic Mail:
Electronic mail (or) email is used to send the message one place to another through the Internet.
Web site:
A collection of web pages closely linked to each other. A company’s presence on the World Wide Web. A web site is merely the entire collection of Web pages relating to a specific topic or owned by a business, group, or individual.
Web page:
A document on the World Wide Web. The term page has nothing to do with the length of the document; some pages are short, and some are very long.
Newsgroup
A discussion area (group) on USENET. A forum where people can read or write their own news messages, and flames. Newsgroups have a certain hierarchical format that replaces spaces with periods.
USENET
Contraction of USEr NETwork, an Internet facility that offers a wide variety of newsgroups, bulletin boards, and public forums.
What is Electronic Mail?
Electronic mail, or e-mail (and mail) for short, is one of the most popular uses of the Internet. Once you have an e-mail account you can send an electronic message (sort of like a letter) to just about anyone else with an e-mail account so long as you know their e-mail address.
If you have an internet service provider (ISP) or commercial online service you probably already have and know your e-mail address (If you don't know it, you can always badger technical support!) Most e-mail addresses are set up like this: it is your username, then an @ ('at') symbol, and then a domain name (something .com, .net, or .org in most cases).
For example, if you are on America Online (AOL) your e-mail address is username@aol.com where username is your AOL screen name. (Contrary to popular belief, not everyone uses AOL, so if you use AOL and someone asks you for your e-mail address, always remember to add the @aol.com part or they might get an error message!)
Using e-mail is rather straightforward. Once you have an account set up, you just select the option that says something like "new e-mail message" or "create a new message". You'll probably be prompted with three boxes (called fields): To:
Subject:
Body: (sometimes the body doesn't actually say body, it's just the big area where you type your actual message.) In the To: field you type the complete e-mail address of the person who will receive the e-mail. You can type anything you want as the subject and body, although the length of the subject is limited. You usually want to keep the subject to just a few words describing the content of the body of the e-mail message.
You may also see options for attachments and forwards. You can add files to your e-mail by using the attachment option. You can forward (make a copy) of a message you receive from someone (if you have their permission if necessary) and mail it to someone else with the forward option.
You may also see fields for CC: and BCC: close to your To: field. CC stands for carbon copy. If you want to send a message to multiple people, add the extra people in the CC: field (usually you separate their e-mail addresses by commas). BCC stands for blind carbon copy. BCC works just like a carbon copy, except the e-mail addresses you type in BCC do not show up to the other recipients. (Example: You send a message To: Mary and BCC: Joey. Joey will see Mary's e-mail address, but Mary won't see Joey's e-mail address because you "blinded" it by putting it in the BCC field.)
There are two things about file attachments you need to be careful of. The first thing is that you need to limit the size of files you are sending. An attachment the size of a floppy disk (1.44MB) can take anywhere from a few seconds to a few hours for someone to receive, depending on the speed of their Internet connection. Get permission before sending large files to someone.
The second reason you need to be careful with attachments is because they are one of the most common ways for computer viruses to spread. As a rule you should never open an attachment from someone you don't know or don't trust. And even if you know the sender, don't open an attachment you are not expecting or an attachment that looks suspicious. Some viruses can destroy all the data on your computer so it's best to play it safe.
UUCP
UUCP (UNIX-to-UNIX Copy Protocol) is a set of Unix programs for copying (sending) files between different UNIX systems and for sending commands to be executed on another system. The main UUCP commands (each supported by a UUCP program) are:
- uucp, which requests the copying of a specific file to another specified system
- uux, which sends a UNIX command to another system where it is queued for execution
- uucico, which runs on a UNIX system as the program that carries out the copying and initiates execution of the commands that have been sent. Typically, this program is run at various times of day; meanwhile, the copy (uucp) and command (uux) requests are queued until the uucico program is run.
- uuxqt, which executes the commands sent by uux, usually after being started by the uucico program The uucico programs are the programs that actually communicate across a network. There are several network protocols (variations on packet size and error-checking) that can be used by uucico programs, depending on the kinds of carrier networks being used.
Telnet
Telnet or TELecommunication NETwork is a network protocol which is mostly used to connect to remote machines over a local area network or the internet. Let us dive into knowing more about telnet through this basic tutorial for beginners.
Telnet was developed in 1969 to aid in remote connectivity between computers over a network. Telnet can connect to a remote machine that on a network and is port listening. Most common ports to which one can connect to through telnet are:
Port 21 - File Transfer Protocol
Port 22 - SSH Remote Login Protocol
Port 23 - Telnet Server
Port 25 - Simple Mail Transfer Protocol (SMTP)
Port 53 - Domain Name Server (DNS)
Port 69 - Trivial File Transfer Protocol (TFTP)
Port 70 - Gopher
Port 80 - Hyper Text Transfer Protocol (HTTP)
Port 110 - Post Office Protocol 3 (POP3)
Telnet can be used to connect to virtually any machine that listens on ports. In other words, you can connect to any machine that has certain ports open. Once connected to a machine, you need to issue unix based commands to interact with the remote service. For example, a user don't need to login, check and send mails only through his email service provider's interface but this can be achieved using simple telnet commands. It is because of this reason that many hackers can send spoofed emails or access information such as which services are running on the remote machine. This is also called banner grabbing or daemon tracking. Black hat hackers can also use telnet to sniff network packets which might contain sensitive information such as usernames and passwords. This is achieved by using telnet and network utilities such as tcpdump and wireshark.
Telnet client and server functionality comes built-in in most operating systems. However, there are several third-party applications like putty client that enable remote connectivity. A user can connect to a remote machine through several access modes such as raw access, SSH access, etc. SSH mode offers encryption and security and hence can prevent eavesdropping by hackers. This is by far the most secure way of connecting to a machine. However, it is necessary that the remote machine supports SSH login to make use of the encryption and security features.
On windows machines, telnet client can simply be started by issuing the telnet command in windows command shell. The following example would help you connect to a remote machine on the HTTP Port 80 and issue a GET command which would fetch a file as your web browser does it behind scenes:
Command Prompt> Telnet
Command Prompt> open (somedomain.com or ip address) 80
At this stage, you would be connected to somedomain.com or ip address on port 80 and the daemon that is running on port 80 (most probably HTTP Server) would be waiting for HTTP requests.
GET / HTTP/1.1
host:
Issuing the command above would make the HTTP Server return the file requested, in this case it would be the default file at the root location.
Most applications and embedded devices make use of the telnet technology to connect to remote server machines and provide end user functionality. The most common use of telnet stands to enable remote authentication and access.
Port 21 - File Transfer Protocol
Port 22 - SSH Remote Login Protocol
Port 23 - Telnet Server
Port 25 - Simple Mail Transfer Protocol (SMTP)
Port 53 - Domain Name Server (DNS)
Port 69 - Trivial File Transfer Protocol (TFTP)
Port 70 - Gopher
Port 80 - Hyper Text Transfer Protocol (HTTP)
Port 110 - Post Office Protocol 3 (POP3)
Telnet can be used to connect to virtually any machine that listens on ports. In other words, you can connect to any machine that has certain ports open. Once connected to a machine, you need to issue unix based commands to interact with the remote service. For example, a user don't need to login, check and send mails only through his email service provider's interface but this can be achieved using simple telnet commands. It is because of this reason that many hackers can send spoofed emails or access information such as which services are running on the remote machine. This is also called banner grabbing or daemon tracking. Black hat hackers can also use telnet to sniff network packets which might contain sensitive information such as usernames and passwords. This is achieved by using telnet and network utilities such as tcpdump and wireshark.
Telnet client and server functionality comes built-in in most operating systems. However, there are several third-party applications like putty client that enable remote connectivity. A user can connect to a remote machine through several access modes such as raw access, SSH access, etc. SSH mode offers encryption and security and hence can prevent eavesdropping by hackers. This is by far the most secure way of connecting to a machine. However, it is necessary that the remote machine supports SSH login to make use of the encryption and security features.
On windows machines, telnet client can simply be started by issuing the telnet command in windows command shell. The following example would help you connect to a remote machine on the HTTP Port 80 and issue a GET command which would fetch a file as your web browser does it behind scenes:
Command Prompt> Telnet
Command Prompt> open (somedomain.com or ip address) 80
At this stage, you would be connected to somedomain.com or ip address on port 80 and the daemon that is running on port 80 (most probably HTTP Server) would be waiting for HTTP requests.
GET / HTTP/1.1
host:
Issuing the command above would make the HTTP Server return the file requested, in this case it would be the default file at the root location.
Most applications and embedded devices make use of the telnet technology to connect to remote server machines and provide end user functionality. The most common use of telnet stands to enable remote authentication and access.
No comments:
Post a Comment