We are all used to using the internet for almost anything we can think of. Some of us shop online, while others of us read news articles, and still others play games! This is all made possible by a networking system called TCP/IP. TCP/IP is an acronym that stands for Transmission Control Protocol and Internet Protocol. All you really need to remember is that TCP/IP is the most popular ways that computers communicate with each other. The first thing we need to cover is how IP addressing works. Each computer on a network has a unique address which identifies it. The address consists of 4 numbers, called octets that are separated by dots. Each number can range in value between 0 and 255. 192.168.3.9 is an example of a valid IP address. In this case the address is telling us that your computer is number 9 on the 192.168.3 network. A good way to think about this is that it is very like a street address for a house or a business. The network number, which you will recall is the first three numbers, is like the street name, while the host or computer number is just like the house number. All of the computers on the same network are neighbors and can talk freely. However, if there are any differences in the first three numbers of the address, which means that the computers are on different networks, the computers can only talk to each other with the aid of a device called a router. A router is just like a mailman that delivers messages on different streets.

                  The CCNA exam will test your ability to understand the Internet Layer of the TCP/IP model, and specifically you must be able to describe the components and structure of an IPv4 address, compare public and private addresses, differentiate between the classes of IP addresses, define the function of DHCP and DNS in IP addressing etc. So let’s see some important concepts below:

– Each internet network host (computer, router, server etc) has its own unique IP address to communicate with other hosts. It is like the unique postal address of our home. There are two versions of IP addresses available. IPv4 and IPv6. The IP version 4 type is the most common today but in the future the IP version 6 will dominate. IPv4 is a 32-bit address and IPv6 is 128-bit address.

– IP addresses can be assigned to hosts either manually or dynamically. Dynamic assignment uses the Dynamic Host Configuration Protocol (DHCP).

– The purpose of DNS is so resolve domain names to IP addresses.

– An IPv4 address (32 bits) is broken into 4 sections with 8 bits each. Although the IP address is a binary number, we represent it into decimal notation.

– An IP address (IPv4) consists of the Network ID (leftmost or high-order bits) and the Host ID (rightmost or low-order bits). The subnet mask specifies what is the Network ID and what is the Host ID. For example an IP address 192.168.10.20 with subnet mask 255.255.255.0 specifies that the Network ID is 192.168.10 and the Host ID is 20. Also, an IP address 10.1.2.30 with subnet mask 255.255.0.0 specifies that the Network ID is 10.1 and the Host ID is 2.30. You get the point now.

– We have public and private IP addresses. Public addresses are always unique but private addresses can be reused in private LAN networks. The Private addresses are within the following ranges:

10.0.0.0 through 10.255.255.255

172.16.0.0 through 172.31.255.255

192.168.0.0 through 192.168.255.255

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