INTERNET ADDRESSES

We can classify the computers connected with Internet in two categories, servers and clients. A server is a computer with the capacity to provide connectivity and sharing to multiple personal computers or clients (any computing device you use to access the Internet), which is specifically set up to serve its files to client computers. The files that a server makes available to your computer can be web pages, videos, sounds, images, etc. A web server normally has:

A high end computer with web server software. The three most popular web server software are:

• Apache HTTP Server, available in public domain
• Microsoft Internet Information Services (IIS)
• Sun Java System Web Server
• A very good Internet connection speed, so that it can support multiple simultaneous users.
• Its own URL and IP address. (What is a URL? URL - Uniform Resource Locator. URL is the global address of a document or resource on the WWW)  

For your home computer to be able to receive files or any data from a server, your computer must request this information. This happens when you enter an URL in your browser or when you receive e-mail. When we work on Internet we come across different types of addresses used for different purposes, like; web address, IP address, email address. Each one has a special syntax, and meaning. It is important for you to know about these addresses, before you start working on Internet.

1.9.1 IP Addresses  

Figure 1.23 shows an IPv4 address: 

IP address: 192.168.1.97 in various forms: 

IPv4 address is a series of four numbers separated by dots (.). The four numbers ranges between 0 and 255. So IPv4 address takes only 4-bytes (or 32-bits) of computer memory. Not all the IPv4 addresses may be used to identify a computer. Some addresses of IPv4 are not used at all due to certain restrictions. In addition, some addresses are reserved, for example; the IP address 255.255.255.255 is used for broadcasts.

Every device, computer, printer or peripheral connected to a TCP/IP network must have its own IP address. Each 32 bit IP address consists of two components:

• Network Identifier (Net ID) – which identifies one of the Networks that is a part of Internet. 
• Device Identifier (Device ID) – which identifies a specific device within the identified Net-ID. 

A Net ID may be of 8 to 24 bits long. By using a subnet mask in combination with their own IP address, you can determine the destination address of the devices is remote or local. For example, consider the IP address 192.168.1.35, having 24 bits Net ID. The remaining 8 bits of this address specifies the device ID. The subnet mask for this network should be 255.255.255.0. This subnet mask is used to identify the IP address of the network.

Now, consider a situation in your office, you want to create a small network, but your network service provider has given you only one IP address? Fortunately, there are IP addresses that have been kept for private network. These addresses are not globally allotted to any organisation but are addresses with in your private network. To connect your private network to the Internet, you are required either to use a network address translator gateway, or a proxy server. Please refer to further readings for more details on these networks. The IP range that is allocated for such non-routable addresses are:

 The subnet mask is similar to an IP address - it is also a 4-byte (or 32-bits) field and can be represented using dot notation. In binary, it always comprise a series of ones, followed by sequence of zeros. The total number of bits is 32, but the number of ones and zeros determines the nature of the mask. By comparing any IP address with a given mask, you can split addresses into two parts, a network ID and a device ID. The following example explains this concept in more details. 

Suppose your computer has an IP address of 193.168.1.35 and you want to access a location 193.168.1.56, as your subnet mask is 255.255.255.0, it will give you following answers:

Since, the Result of both the operation points to same Net ID, therefore, you can conclude that the referred destination IP address is local. Now, suppose your computer has an IP address of 191.168.1.35 and your NetID is 16 bit long. Suppose you want o access a location 190.168.1.35. Since, you have 16 bit NetID, therefore, your network subnet mask will be 255.255.0.0, it will give you following answers:

Since, the Result of both the operation points to different Net ID, therefore, you can conclude that the referred destination IP address is remote.

By comparing the source network ID with the IP address of the source and the network ID of the destination IP address, you can easily determine if the destination is within the same subnet. A web page request, thus, can be identified as local page or a page from remote server. But, how do you find the location of the remote server? The answer to this question is beyond the scope of this unit. However, you should know that routers may be responsible in finding the final path to the remote server.

As the numbers of users are increasing, the IPv4 addresses will run short. Therefore, a 128 bit Internet Protocol Version 6 (IPv6) was designed which is at present actively being deployed on the Internet. This series can provide up to 3.4 X 1038 addresses. For more details on IPv6, please refer to Further Readings.

1.9.2 DNS and Web Addresses 

An Internet or Web address is used to view a web page. When you are viewing a Web page, the web address of the page appears in the Address bar in the browser. In the previous section, you have gone through the concept of IP addresses. What do you think about the IP address? Are they not very cumbersome to remember? For example, to visit IGNOU website the address www.ignou.ac.in is far simpler than that of an IP address like 190.10.10.247. Obviously, what we want to use are simpler textual domain addresses instead of complex IP addresses. However, to enable the use of simple textual address, you will require a service that will map these text based names to respective IP addresses automatically. Such a service was designed in 1983 by the University of Wisconsin with the name Domain Name System (DNS).

In the present day, Internet, Domain Name System (DNS) should keep track of address of each computer or any other internet device and email addresses. The name servers translates the web address or email address to respective IP address. For example, the name server translates address like www.ignou.ac.in into a computer understandable IP address. It sounds simple, but remembers on Internet you are dealing with million of addresses and every day this list is increasing. All these computers have a unique address. Therefore, DNS follows a hierarchical naming scheme that is supported by distributed database system to ensure no duplicate names are issued at all. Figure 1.24 shows the hierarchical structure of domains names on Internet. For example, traversing the hierarchy from the top you can track down ignou.ac.in as:  

First you can find the in (India) in the top level country domains. Within this domain find the ac (Academic) sub domain. Please note most of the Indian Universities will be in this sub-domain. Finally, in the ac you can find the entry for ignou. This entry should point to the IP address for the ignou.ac.in for the WWW as well as for the mail server. This is how the DNS finds the addresses, thus, is a very efficient system.

Thus, using the DNS you will be able to relate a given textual address to IP address. For converting domain name into IP address, it first accepts request from programs and other servers. After accepting the request, the name server can do the following:

• If it knows the IP address of requested domain, it will answer the request with an IP address of the requested domain.  
• If it does not know the requested domain name, it will contact another name server and try to find the IP address.
• If the requested domain name is invalid or domain does not exist, it will return an error message. 

 But how can you name a web page on the Internet? To answer this question you may first identify that a web page actually is part of a website that may reside on a web server having a unique IP address. Thus, to identify a web page you need to identify –

• The protocol used to access that page.
• The server on which the website is located.
• The name of the page within that web site. Please note that simple web pages are stored as files.  

Please note that a web page may be stored as a single or multiple files.

Thus, to identify a web page you will have an address like: 

http://www.ignou.ac.in/students/result.html

• the address as above recognizes the protocol http (Hyper Text Transfer Protocol) to access the page,
• the www.ignou.ac.in identifies the DNS name of IGNOUs WWW server, and 
• the name of the page accessed by you is result.html which resides in the students folder within the website.  

This address is called the URL. URL stands for Uniform Resource Locater.

You can now clearly see that a URL consists of three parts – the first part is used to tell the browser what kind of server it will connect to. In the example above, the browser will connect to a web server using Hypertext Transfer Protocol (HTTP). Other protocols that we can use in this field of an URL are FTP, smtp etc. the protocol is always followed by ―://‖

The second part of an URL is a fully Qualified Domain Name (www.ignou.ac.in). In an URL, the fully qualified domain name identifies the site running the server. Web servers use port 80 by default, but some servers has been set up to use other ports. For this, a URL can contain a port number following the domain name and separated from it by a colon (www.ignou.ac.in:80), it is optional to write a port number with domain name. If the URL contains no port number, the default port is used.(The range of Well Known Ports is in between 0–65535)

The first two parts of an URL are used to identify the web server of the website. Each web server has a home page and a directory to store the entire document related to the web page like images, audio, video files.

The third component of URL is an optional pathname for a particular document itself. For example, the address http://www.ignou.ac.in/students/result.html specifies the file result.html i.e., in the directory students (/students/result.html) in the specified web server.

But how does this information exchange between the web client and web server is achieved? This whole communication is managed by a protocol called the Hyper Text Transfer Protocol (HTTP). However, the only protocol that works on Internet as told to you in the previous section was TCP/IP. So what is this HTTP? Please note HTTP can work only over a connection that is managed by TCP. Thus, it is a higher level protocol that uses the services of TCP. 

HTTP specifies the list of actions that lead to transfer of a requested information exchange between a web client and web server. Whenever you wish to visit a web page on the internet, you request that page from a web server. When you type a URL into your browser (for example, "http://www.abc.com/"), your web browser requests the page (or file) named index.html from the web server and the web server sends the page back to the web browser. Let us identify these steps in more details: (URL - Uniform Resource Locator – identifies the GLOBAL address of a document or) 

1) As a first step you may put a URL like http://www.abc.com/index.html or equivalent Domain name www.abc.com as the address of the website that you want to access through your web browser.

2) The Web browser tries to resolve the IP address of the website www.abc.com by the information available in its own cache memory. If web server does not have the information about IP address stored in its cache, it requests the IP address from Domain Name System (DNS) servers. The DNS server tells the browser about the IP address of the website. 

3) Once the web browser knows the IP address of the website, it then requests the web page (index.html page which is the home page in the present example) from the web server. 

4) The web server responds by sending back the requested web page. If the requested page does not exist then it will send back the appropriate error message. 

5) Your web browser receives the page from the web server and displays it as per the display requirements of the web page. 

1.5.3 E-mail Addresses 

As you have studied earlier that e-mail is one of the popular services increasingly being used by people in their daily life. The following can be a typical email address format on Internet for any e-mail service provider like, Gmail, Rediff, Yahoo, MSN, or any network (domain) name etc.

The username in general is the name assigned or chosen during creation of an email account. Sub-domain are domain we have already discussed in above section, in case of private service provider it is generally its own name like abc@yahoo.com, abc@yahoo.co.in, abc@gmail.com, etc. On the Internet you can see both kind of domains non-Geographic and geographic domains. Lets take an example to better understand an e-mail address: In an e-mail address “naveen@ignou.ac.in”, naveen indicates the username, the sub-domain named IGNOU (Indira Gandhi National Open University) which is an academic organisation (.ac) and is situated in country India (.in).

Check Your Progress 3 👈

1. What are the services on Internet? …………………………………………………………………………………… …………………………………………………………………………………… 

2. What is firewall? Where can it be used? …………………………………………………………………………………… …………………………………………………………………………………… 

3. What it TCP/IP? Why is it used? …………………………………………………………………………………… …………………………………………………………………………………… 

4. What is a URL?

 …………………………………………………………………………………… …………………………………………………………………………………… 

5. Define the terms DSN, IPv4 address, Subnet mask …………………………………………………………………………………… ……………………………………………………………………………………