NETWORKING BASICS

Published: February 19, 2022

Last Modified: April 7, 2023

NETWORKING BASICS:

IP Addresses

Internet Protocol address is the abbreviation of IP address.
Each digital device (computer, laptop, phone, tablet, etc.) is assigned an IP address, and this is what enables us to communicate and connect with devices. Imagine an IP address as similar to your house address. Without that address, no one could find you or send you snail mail. 
💠 The IP address system we are presently using is known as IP version 4, or IPv4.  It is made up of 32 bits of four octets, or four groups of 8 bits (on/off switches).
💠For instance, 192.168.1.101. Each of the numbers between the periods (.) is the decimal equivalent of 8 bits. This means that we calculate the base 2 number that computers use represented by the 8 bits and convert them to decimal numbers that humans are more accustomed to working with. Each one of the octets (8 bits) is capable of representing numbers within the range 0 through 255 (2 to the 8th power).
✳️ Classes of IP Addresses:
💠 IP addresses are generally put into three classes, and the ranges are:
🔹Class A: 0.0.0.0 – 127.255.255.255
🔹 Class B: 128.0.0.0 – 191.255.255.255
🔹 Class C: 192.0.0.0 – 223.255.255.255
💠 Later, we will address subnetting and subnet masks that vary with these different IP classes.
✳️ Public vs. Private IP Addresses
💠 It’s important to note that our IP address system has its limitations. The biggest limitation is that there are not enough IP addresses to cover all of the devices that need to connect to the internet. The IPv4 system that we are working with now has only 4.3 billion IP addresses. With 7.3 billion people on the planet and far more devices, that certainly is not enough.
💠 As a result, a system was developed to reuse a group of IP addresses to be used within a LAN—and are not usable over the internet. These addresses can be used over and over again within each local area network, but not over the internet, thereby conserving the number of IP addresses necessary to keep the world going ’round.
✅ These private addresses include:
🔹192.168.0.0 – 192.168.255.255
🔹10.0.0.0 – 10.255.255.255
🔹172.16-.0.0 – 172.16.255.255
✅ You have probably seen the private IP addresses beginning with 192.168.xxx.xxx or 10.xxx.xxx.xxx on your Kali system when you type ifconfig.
💠 This is your private IP that is only usable on the local area network. To communicate over the internet, it must be translated to a public IP by a NAT device 
💠 Dynamic Host Configuration Protocol (DHCP) assigns IP addresses dynamically. This means that you do not have the same IP address all of the time. Most of the time, these IP address assignments are on a local area network. Remember, on LANs we use private IP addresses. When each device is connected to the LAN, it must request an IP address. That device sends that request to the DHCP server that then assigns an IP address to that system for a fixed length of time known as a “lease.”
💠 Each time you connect to the LAN, you are likely to receive a different (dynamic) IP address, but usually in the same range. For instance, 192.168.0.0 – 192.168.255.255.
✳️ NAT
💠 Network Address Translation (NAT) is protocol whereby internal private IP addresses are “translated” to an external public IP address that can be routed through the internet to its destination. Remember, private IP addresses of the systems inside the LAN cannot use their IP addresses on the internet because they are not unique (every LAN uses basically the same IP addresses inside their network).
💠 The NAT device accepts requests to traverse the internet from an internal machine. It then records that machine’s IP address in a table and converts the IP address to the external IP address of the router. When the packet returns from its destination, the NAT device looks into its saved table of the original request and forwards on the packet to the internal IP address of the system that made the original request within the LAN. When working properly, the individual systems and users don’t even realize this translation is taking place.
🌀LAN: LAN stands for “Local Area Network” and refers to a network that is not publicly accessible by the internet. Examples of this are home or office network.
🌀WAN: WAN stands for “Wide Area Network” and generally refers to large dispersed networks and, more broadly, the internet.
🌀ISP: ISP stands for “Internet Service Provider” and refers to the company responsible for providing you access to the internet.
🌀NAT: Network Address Translation allows requests from outside your local network to be mapped to devices within your local network.
🌀Firewall: A firewall is a piece of hardware or software that enforces what type of network traffic is and is not allowed. This is generally done by establishing rules for which ports should be externally accessible.
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