Since Cisco Certifications are always hot and the Cisco CCNA is the most popular from all, I decided to start a series of articles regarding important topics that you need to be prepared for passing the CCNA 640-802 composite exam. These topics will be also useful for people taking the two-exam option (ICND1 640-822 and ICND2 640-816).
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
– As the number of networks grew, the IP addresses were broken into categories called classes to accommodate different sizes of networks. We have five classes of IP addresses. Class A, B, C, D, E.
– Any address that starts with a value between 1 and 126 in the first decimal octet is a Class A address. E.g 10.1.2.24 is a Class A address.
– Any address that starts with a value in the range of 128 to 191 in the first octet is a Class B address. E.g 172.16.1.27 is a Class B address.
– Any address that starts with a value in the range of 192 to 223 in the first octet, it is a Class C address. E.g 192.168.5.1 is a Class C address.
– An IP address that starts with a value in the range of 224 to 239 in the first octet is a Class D address. Class D address range is used for multicasting. E.g 18.104.22.168
– Any address that starts with a value between 240 to 255 is a Class E address. These addresses are reserved and not used anywhere.
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