Internet Addressing

1. Internet Addressing

2. When your computer is on the Internet, anything you do requires data to be transmitted and received. • For example, when you visit a web site, such as google.com, data is transmitted to your computer in order to load the content of the web page. • The server where google.com is located needs to know where to send the data. • Network layer • When you connect to google.com, it receives your IP Address and then knows where to send the data.

3. Every machine on the Internet­ has a unique identifying number, called an IP Address. • Without a unique IP address on your machine, you will not be able to communicate with other devices, users, and computers on the Internet. • You can look at your IP address as if it were a telephone number, each one being unique and used to identify a way to reach you and only you.

4. A typical IP address looks like this: • 216.27.61.137 • ­To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a "dotted decimal number" like the one above. But computers communicate in binary form. • Look at the same IP address in binary: • 11011000.00011011.00111101.10001001

5. There are three common ways in which IP address can be represented. • There is the binary notation which uses base two number system to represent numbers. For ex – 11011000.00011011.00111101.10001001  • There is the decimal notation which uses base ten number system to represent numbers. For ex – 254.202.52.23 • There is the hexadecimal notation which uses the base sixteen number system to represent numbers. For ex - E3:F4:C8:A5

6. ­The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers. Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between 0 and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique values!

7. Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts.

8. Every IP address that is exposed to the public Internet is unique. In contrast, IP addresses within a local network use the same private addresses; thus, • a user's computer in company A can have the same address as a user in company B and thousands of other companies. However, private IP addresses are not reachable from the outside world.

9. IP address classes • These IP addresses can further be broken down into classes. These classes are A, B, C, D, E and their possible ranges can be seen in Figure 2 below. • Class Start address Finish address • A 0.0.0.0 126.255.255.255 • B 128.0.0.0 191.255.255.255 • C 192.0.0.0 223.255.255.255 • D 224.0.0.0 239.255.255.255 • E 240.0.0.0 255.255.255.255

10. IP address classes, Network and Host

11. Private Addresses • There are also blocks of IP addresses that are set aside for internal private use for computers not directly connected to the Internet. These IP addresses are not supposed to be routed through the Internet, and most service providers will block the attempt to do so. These IP addresses are used for internal use by company or home networks that need to use TCP/IP but do not want to be directly visible on the Internet. These IP ranges are:

12. Class Private Start Address Private End AddressA 10.0.0.0 10.255.255.255B 172.16.0.0 172.31.255.255C 192.168.0.0 192.168.255.255If you are on a home/office private network and want to use TCP/IP, you should assign your computers/devices IP addresses from one of these three ranges. That way your router/firewall would be the only device with a true IP address which makes your network more secure.

13. If you look at the table you may notice something strange. The range of IP address from Class A to Class B skips the 127.0.0.0-127.255.255.255 range. That is because this range is reserved for the special addresses called Loopback addresses that have already been discussed above.

14. The Address Itself (Loopback Address) • Out of these addresses there are 3 special ranged that are reserved for special purposes. The first is the 0.0.0.0 address and refers to the default network and the 255.255.255.255 address which is called the broadcast address. These addresses are used for routing, which will not be covered in this tutorial. The third address, 127.0.0.1, is the loopback address, and refers to your machine. Whenever you see, 127.0.0.1, you are actually referring to your own machine. That means if you clicked on this link, http://127.0.0.1, you are actually trying to connect to your own computer, and unless you have a web server running, you will get a connection error.

15. Default Network: The special network 0.0.0.0 is generally used for routing. • Class A: From the table above you see that there are 126 class A networks. These networks consist of 16,777,214 possible IP addresses that can be assigned to devices and computers. This type of allocation is generally given to very large networks such as multi-national companies. • Loopback: This is the special 127.0.0.0 network that is reserved as a loopback to your own computer. These addresses are used for testing and debugging of your programs or hardware. • Class B: This class consists of 16,384 individual networks, each allocation consisting of 65,534 possible IP addresses. These blocks are generally allocated to Internet Service Providers and large networks, like a college or major hospital.

16. Class C: There is a total of 2,097,152 Class C networks available, with each network consisting of 255 individual IP addresses. This type of class is generally given to small to mid-sized companies. • Class D: The IP addresses in this class are reserved for a service called Multicast. • Class E: The IP addresses in this class are reserved for experimental use. • Broadcast: This is the special network of 255.255.255.255, and is used for broadcasting messages to the entire network that your computer resides on.

17. Static and Dynamic IPNetwork infrastructure devices such as servers, routers and firewalls are typically assigned permanent "static" IP addresses. The client machines can also be assigned static IPs by a network administrator, but most often are automatically assigned temporary "dynamic" IP addresses via software that uses the "dynamic host configuration protocol" (see DHCP). Cable and DSL modems typically use dynamic IP with a new IP address assigned to the modem each time it is rebooted.

18. Logical vs. PhysicalAn IP address is a logical address that is assigned by software residing in a server or router (DHCP). In order to locate a device in the network, the logical IP address is converted to a physical address by a function within the TCP/IP protocol software (ARP). The physical address is actually built into the hardware (MAC address).

19. IPv4 and IPv6 Addresses • There are two flavors of IP Addresses that can be used on a network. • The first, and the version that the Internet and most routers are currently configured for, is IPv4 or Internet Protocol version 4. • This version uses 32-bit addresses, which limits the amount of addresses to 4,294,967,296 possible unique addresses. • Some of these addresses, about 290 million, are also reserved for special purposes.

20. IPv6 is going to solve a few major problems: • IP address contains two parts. The first part is the network identifier and the second is the host identifier in that network. Not all the addresses in a specific network are going to be used, which is very wasteful. • The Internet is growing rapidly. Many organizations have more than a single LAN, and wireless networks are also going to be used more and more in the future. • There is an increased usage in IP addressing in many new areas. Not only computers can be connected to a network, but also other electric devices can be controlled using the SNMP protocol. (Mobiles) • There are advantages of giving multiple addresses per host, The problem - an increase in the number of addresses in use.

21. All of these problems are solved in IPv6 because the new address in IPv6 is constructed from 128 bits instead of 32 bits and it is going to increase the address space by 2128. • IP addresses change significantly with IPv6. IPv6 addresses are 16 bytes (128 bits) long rather than four bytes (32 bits). This larger size means that IPv6 supports more than • 300,000,000,000,000,000,000,000,000,000,000,000,000 – 38 0’s

22. In the coming years, as an increasing number of cell phones, PDAs, and other consumer electronics expand their networking capability, the smaller IPv4 address space will likely run out and IPv6 address become necessary.IPv6 addresses are generally written in the following form:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh

23. "IP Conflict" There are some guidelines to how IP address can appear, though. The four numbers must be between 0 and 255, and the IP address of 0.0.0.0 and 255.255.255.255 are reserved, and are not considered usable IP addresses. IP addresses must be unique for each computer connected to a network. That means that if you have two computers on your network, each must have a different IP address to be able to communicate with each other. If by accident the same IP address is assigned to two computers, then those computers would have what is called an "IP Conflict" and not be able to communicate with each other.

24. How to find your IP Address? • Windows -- Though you can click through the user interface to find your network interface settings, one quick way to find your IP address is to open the Command Prompt application from Accessories and enter this command: ipconfig