What is Internet addressing? A way to locate people, computers, and Internet resources. It can be • •
IP (Internet Protocol) addresses and domain names Electronic mail addresses
•
URLs
In general, Internet addressing is a systematic way to identify people, computers and Internet resources. On the Internet, the term "address" is used loosely. Address can mean many different things from an electronic mail address to a URL. 1.IP Address An IP address is a unique number that identifies computers on the Internet; every computer directly connected to the Internet has one. Every client, server and network device must have a unique IP address for each network connection (network interface). IP addresses are conceptually similar to phone numbers, except they are used in LANs (Local Area Network), WANs (Wide Area Network), and the Internet. Because the numbers are not easy for humans to remember, the Domain Name System provides a service analogous to an address book lookup called "domain name resolution" or "name resolution". Special DNS servers on the internet are dedicated to performing the translation from a domain name to an IP address and v.v. An IP address consists of four numbers separated by periods. Each number must be between 0 and 255. An example is: 204.81.205.32 The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address. Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates. The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Four regional Internet registries -- ARIN, RIPE NCC, LACNIC and APNIC -- assign Internet addresses from the following three classes. •
Class A - supports 16 million hosts on each of 126 networks
• •
Class B - supports 65,000 hosts on each of 16,000 networks Class C - supports 254 hosts on each of 2 million networks
Format. An IP address is made up of four bytes of information (totaling 32 bits) expressed as four numbers between 0 and 255 shown separated by periods. For example, your computer's IP address might be 238.17.159.4, which is shown below in humanreadable decimal form and in the binary form used on the Internet.
Example IP Address Decimal: Binary:
238 . 17 . 159 . 4 11101110 00010001 10011111 00000100
Each of the four numbers uses eight bits of storage, and so can represent any of the 256 numbers between zero (binary 00000000) and 255 (binary 11111111). Therefore, there are more than 4 billion possible different IP addresses in all: (Internet Protocol address) The address of a device attached to an IP network (TCP/IP network). Every client, server and network device must have a unique IP address for each network connection (network interface). Every IP packet contains a source IP address and a destination IP address. Static and Dynamic IP Each device in an IP network is either assigned a permanent address (static IP) by the network administrator or is assigned a temporary address (dynamic IP). Depending on one's Internet connection the IP address can be the same every time one connects (called a static IP address), or different every time one connects, (called a dynamic IP address). In order to use a dynamic IP address, there must exist a server, which can provide the address. IP addresses are usually given out through a server service called DHCP or the Dynamic Host Configuration Protocol. If a static address is used, it must be manually programmed into parameters of the device's network interface. Routers, firewalls and proxy servers use static addresses. Client machines may use static or dynamic IP addresses.In routers and operating systems, the default configuration for clients is dynamic IP . Dotted Decimals IP addresses are written in "dotted decimal" notation, which is four sets of numbers separated by periods; for example, 204.171.64.2. If you knew the IP address of a Web site, you could enter the dotted decimal number into your browser instead of the domain
name .The traditional IP address uses a 32-bit number that defines both the network and the host computer. The network class determines how many of the 32 bits are used for the network address, leaving the remaining bits for use as the host number. The host number can be further divided between subnetworks and hosts Class A, B and C Although the computer identifies the class by the first three bits of the address (A=0; B=10; C=110), people identify the class by the first number in the address (see range below). This class-based system has also been greatly expanded, eliminating the huge disparity in the number of hosts that each class can accommodate
Class A B C
Maximum Maximum Class Number Hosts Number of per Range Networks Network 1-126 127 16,777,214 128-191 16,383 65,534 192-223 2,097,151 254 127 reserved for loopback test
Number of Bits used in Network/Host ID ID 7/24 14/16 21/8
An IP address is first divided between networks and hosts. The host bits are further divided between subnets and hosts.
More detail The Internet Protocol (IP) knows each logical host interface by a number, the IP address. On any given network, this number must be unique among all the host interfaces that communicate through this network. Users of the Internet are sometimes given a host name in addition to their numerical IP address by their Internet service provider. The IP addresses of users browsing the World Wide Web are used to enable communications with the server of the web site. Also, it is usually in the header of email messages one sends. In fact, for all programs that utilize the TCP/IP protocol, the sender IP address and destination IP address are required in order to establish communications and send data. Internet addresses are needed not only for unique enumeration of hosted interfaces, but also for routing purposes, therefore a high fraction of them are always unused or reserved. The unique nature of IP addresses makes it possible in many situations to track which computer — and by extension, which person — has sent a message or engaged in some other activity on the Internet. This information has been used by law enforcement authorities to identify criminal suspects. The dynamically-assigned nature of many IP addresses can make this more difficult.
Domain Name Most computers on the Internet have a unique domain name. Special computers, called domain name servers, look up the domain name and match it to the corresponding IP address so that data can be properly routed to its destination on the Internet. An example domain name is: healthyway.com Domain names are easier for most people to relate to than a numeric IP address. 2.Electronic Mail Address An Internet electronic mail, or e-mail, address is used to identify a person (or persons) and a computer for purposes of exchanging electronic mail messages. An example Internet e-mail address is:
[email protected] Internet e-mail addresses are read from left to right: • • •
"abc123" is the name of the person receiving or sending the message; this is referred to as the username. "columbia" is part of the domain name of the organization. "edu" is also part of the domain name and indicates that "columbia" is an educational institution.
Electronic Mail Address Other networks may use different electronic mail addressing schemes within their own networks. To be used in Internet e-mail, these addresses often need to be modified. For example, within CompuServe an e-mail address consists only of two numbers separated by a comma: 36547,891. • •
To convert this to an address that can be used on the Internet, the comma is changed to a period and the number serves as the username. The domain name is compuserve.com, so the Internet address would be:
[email protected]
3.URLs URL stands for Uniform Resource Locator. URLs are used to identify specific sites and files available on the World Wide Web.
The structure of a URL is: protocol://server.subdomain.top-leveldomain/directory/filename Not all URLs will have the directory and filename. Two examples: http://www.healthyway.com/exercise/mtbike.html gopher://gopher.state.edu/ URLs Similar to an e-mail address, a URL is read like a sentence. For example the URL http://www.healthyway.com is read as "http colon forward slash forward slash www dot healthyway dot com". In Summary: Internet addressing is used to identify people, computers, and Internet resources. Using the Internet requires an understanding of different addressing schemes. People are identified with electronic mail addresses. Computers are identified with IP addresses and domain names. Resources and files available through the World Wide Web are identified using URLs.
