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Series of Network Fundamentals #4 (IPv4 & IPv6 Address),to get started in Cyber Security.

Hello everyone, I’m back with 4th series of Network Fundamentals, in the last blog we learned about Topologies, in this blog we are going to learn about the IP Addresses.

Let’s start,

Internet Protocol v4 (IP) address

What is IP address

Internet Protocol address is a unique identifier of computer systems on the network to communicate between different host, IPv4 is a 32 bit address, which is in a octet format, separated by “.”(dots) and IP addresses are registered and assigned by, The Internet Corporation for Assigned Names and Numbers (ICANN).


32 bit — 10000111011010010011000010001001
Decimal notation (octet) —

In below image we can see the Class, Range and Subnet mask.

In above image you can see between class A & B the “127” number is missing, because is a Loop back address, it is used to self ping or troubleshooting.

What is APIPA?

APIPA stands for Automatic Private Internet Protocol Addressing, when the DHCP server fails to assign the IP address,the APIPA address will assign the temporary IP address for the host and the range of APIPA is to

In below image you can see the Private range of IP address.

Class A IP address are reserved for Large scale companies, Class B IP address are reserved for Medium Scale companies, and Class C IP address are reserved for Small scale companies.

Subnet mask

What is Subnet mask

Subnet mask is used to identify and classify between network Id and host Id of IP address so the computer can determine the host is on the same network or different network.

What is Network ID

It is used to identify, to which network the IPv4 address belongs to.

What is Host ID

It is used to identify, to which computer device the IPv4 address belongs to in LAN network.


IP address —
Network ID — 192.168.10
Host ID — 1

Table of Default Subnet mask of class A,B & C and classifying the bits of Network ID and Host ID

Image from GOOGLE

Subnet mask is also called as CIDR (Classless Inter Domain Routing), which is denoted by (/) Slash notation, after the IP Address.

If you see the IP Address “” that means “/25” is classifying the 25 network bits.

Image by Powercert VIdeos.

You can see in the above image the “/25” is the 1’s of the binary digits are Network ID and the remaining 0’s are Host ID.


What is Subnetting

Subnetting is the process of transferring the number of Host bits to the Network bits.

When the IPv4 address got exhausted, “ICANN” introduced the Subnetting and NAT(Network Address Translation) to resolve the wastage of the Private and Public IP address.

Formula for Subnetting

Internet Protocol (IP) v6

Image from GOOGLE

IPv6 is a updated version of IPv4 address, Which is developed to deal with the exhaustion of IPv4 address, which is 128 bit address, 2¹²⁸ more than billions IP address. which is denoted in a quartet/groups format, separated by colon (:), total number of quartet’s are 8, each quartet consists of 16 bits and each hexadecimal character consists of 4 bits.


The same IP address, also can be written in FEC0::1:2a:1af:11at this format. in the below image you can see the compressed IPv6 addresses.

Image from GOOGLE

Types of IPv6 address

In IPv6 address there are 3 types of IP address
1) Unicast address
2) Multicast address
3) Anycast

1) Unicast address

Sending packets to single address/unique address is called unicast address.

Image from GOOGLE

2) Multicast Address

Sending packets to multiple address from one source is called multicast address.

Image from GOOGLE

3) Anycast Address

The group of devices represented by one IP address, when you send a packet to that IP address it will only deliver to the one member of group that is also the closest member of the group is called Anycast Address.

Image from GOOGLE

Types of Unicast Address

1) Global Unicast
2) Unique Local unicast
3) Link Local Unicast

1) Global Unicast

Global Unicast is similar like Public IP address from IPv4, which starts from 2000::/3 or 3000::/3, it is to be considered as Global unicast address.

2) Unique Local Unicast

Unique local unicast is similar like Private IP address from IPv4, which starts from FD00::/8 or FC00::/7, it is to be considered as Unique local.

3) Link Local Unicast

Link Local Unicast is default IP address on every IPv6 enabled interface, which starts from FE80::/10, it is to be considered as Link Local Unicast and it is non-routable.

I hope you understood the above write-up, if you have any doubt or to add any content let me know in comment section

The next write-up is about Port numbers and Protocols.

Additional Links,
1) Brief history of IPv4 Exhaution.
2) TryHackMe CTF challenge on IP Address.

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