IPv4 - Internet Protocol Version 4

What is IPv4?

IPv4 is the fourth version of the Internet Protocol [IP], widely used to identify devices on a network through an addressing system.
It was introduced in 1981 by DARPA and became the first deployed version for production use on SATNET and ARPANET in 1982 and 1983, respectively.
IPv4 addresses are 32-bit numbers written in Decimal Notation, consisting of four decimal values separated by dots, each ranging from 0 to 255.
These numbers are converted into binary [0s and 1s] to be processed by computers.
An example of an IPv4 address is 172.16.254.1:

Parts of IPv4:

An IPv4 address consists of three parts: the Network Part, the Host Part, and, optionally, the Subnet Number.

Network Part - This portion identifies the specific network the address belongs to and determines the class of the network [e.g., Class A, B, C].
It is used to route traffic to the appropriate network.

Host Portion - The host portion uniquely identifies each device [or host] within the network.
This allows each device on the network to be differentiated and addressed individually.

Subnet Number [Optional] - Used when large local networks are divided into subnets for organizational or efficiency purposes.
Subnets allow for more efficient use of the available IP addresses within a network by breaking it into smaller divisions.

Characteristics of IPv4:

32-bit Addressing - IPv4 uses a 32-bit address, which allows for approximately 4.3 billion unique addresses.
VLSM [Variable-Length Subnet Masking] - IPv4 supports the use of different subnet masks across a network,
allowing for flexibility in dividing the network.
Unicast, Broadcast, and Multicast Addresses - IPv4 supports three types of addressing:
1. Unicast: Sending data to a single recipient.
2. Broadcast: Sending data to all devices in the network.
3. Multicast: Sending data to a specific group of devices.
DHCP [Dynamic Host Configuration Protocol] - Networks can be configured either manually or automatically using DHCP,
which assigns IP addresses to devices dynamically.
Packet Fragmentation - IPv4 allows routers to fragment packets to fit the Maximum Transmission Unit [MTU] of the network.
RIP [Routing Information Protocol] - IPv4 supports RIP, a simple routing protocol used to manage routing information between routers.
Address Representation - IPv4 addresses are represented numerically, with each octet [8 bits] separated by a dot [e.g., 172.16.254.1].
ARP [Address Resolution Protocol] - IPv4 uses ARP to map IP addresses to MAC addresses on a local network.
Header Fields - IPv4 headers contain 12 fields with a total length of 20 bytes, including the source and destination addresses,
packet length, and other control information.

The Classes of IPv4 Addresses:

Class A - This class of IP addresses uses the first octet to represent the network portion,
and the remaining three octets to represent the host portion.
Class A addresses range from 1.0.0.0 to 126.0.0.0 and are intended for very large networks.

Class B: This class of IP addresses uses the first two octets to represent the network portion,
and the remaining two octets to represent the host portion.
Class B addresses range from 128.0.0.0 to 191.255.0.0 and are intended for medium-sized networks.

Class C: This class of IP addresses uses the first three octets to represent the network portion,
and the remaining octet to represent the host portion.
Class C addresses range from 192.0.0.0 to 223.255.255.0 and are intended for small networks.

Class D: This class of IP addresses is used for multicasting.
Multicast addresses begin with the binary pattern of 1110 in the first four bits of the first octet.
Class D addresses range from 224.0.0.0 to 239.255.255.255.

Class E: This class of IP addresses is reserved for experimental use and is not used for general networking purposes.
Class E addresses range from 240.0.0.0 to 255.255.255.255.

Subnet Mask

A subnet mask is a 32-bit number that is used to determine which part of an IP address belongs to the network and which part belongs to the host.
It works by masking off the network portion of an IP address to identify the host portion.
In IPv4, subnet masks are commonly used to divide a network into smaller sub-networks,
allowing for better organization and management of network resources.

CIDR [Classless Inter-Domain Routing] notation is a compact representation of an IP address and subnet mask.
CIDR notation consists of the IP address followed by a slash [/] and a number that indicates the number of network bits in the subnet mask.
For example, 192.168.0.0/24 represents an IPv4 address with a subnet mask of 255.255.255.0.
/8, /16, and /24 are common subnet mask values used to create smaller sub-networks within a larger network.
A subnet mask of /8 [255.0.0.0] creates a very large network with up to 16,777,216 hosts.
This type of network is typically used by large organizations or internet service providers.
A subnet mask of /16 [255.255.0.0] creates a moderately sized network with up to 65,536 hosts.
This type of network is often used by mid-sized organizations or for regional network deployments.
A subnet mask of /24 [255.255.255.0] creates a smaller network with up to 256 hosts.
This type of network is commonly used for small office or home office networks, as well as for point-topoint connections.

Advantages of IPv4:

1. Efficient Data Communication - IPv4 efficiently handles multicast communication, allowing for the delivery of data to multiple devices within a network.
2. Scalability in Routing - IPv4 routing is scalable and efficient, using hierarchical addressing to simplify routing table management.
3. Redefined Addressing - IPv4 addresses allow for efficient encoding and data transmission, contributing to its widespread use.
4. Widespread Adoption - IPv4 has been deployed globally with over 85,000 functional routers supporting the protocol.
5. Security - IPv4 supports encryption methods that help maintain privacy and security when transmitting data.
6. NAT Compatibility - IPv4 easily supports NAT [Network Address Translation],
allowing multiple devices to share a single public IP address without conflict.

Limitations of IPv4:

1. Exhaustion of IP Addresses - Due to the 32-bit address space, the supply of unique IPv4 addresses is becoming scarce, leading to the adoption of IPv6.
2. Need for IP Address Classe - With IPv4, large networks require the use of IP address classes to accommodate multiple hosts, which can be inefficient.
3. Security and Scalability Issues - The reliance on IPv4 for certain security protocols, such as IPsec, complicates network setups.
4. Packet Fragmentation and Routing Overhead - Packet fragmentation adds overhead to routing decisions and introduces latency.
5. Transition to IPv6 - IPv4’s limitations in addressing and routing complexity have necessitated the development of IPv6,
which addresses many of these concerns.
6. Complex Network Configuration - IPv4 networks can become complex to configure,
particularly in environments requiring non-hierarchical addressing,
large routing tables, and features like security, mobility, and multicasting.

Conclusion

IPv4 has been the cornerstone of internet communication, providing a system of unique addresses that allows devices to interact across networks.
Composed of four numerical blocks, IPv4 has enabled the successful growth and operation of the internet for decades.
Although it faces limitations-most notably the exhaustion of available addresses-IPv4 has played an essential role in directing data to its correct destination and remains widely used.
Its contributions to the expansion of global connectivity are undeniable, despite the growing need for IPv6 to address modern network demands.

IPv6 - Internet Protocol Version 6

The Internet Protocol version 6 [IPv6] is the latest version of the Internet Protocol [IP],
which is essential for identifying and locating computers on the Internet.
Developed by the Internet Engineering Task Force [IET], IPv6 was introduced to address the exhaustion of IPv4 addresses.
With a 128-bit address space, IPv6 offers a significantly larger address pool than IPv4, utilizing a hexadecimal format separated by colons [:].

IPv6 Address Format

128-bit address - Comprises eight groups, with each group representing 2 bytes [16 bits].
Hexadecimal format - Each hex-digit corresponds to 4 bits [1 nibble].
Delimiter: Colons [:] separate the groups.

Need for IPv6

Resource Allocation - IPv6 introduces traffic class and flow label fields for enhanced resource allocation,
supporting real-time traffic like audio and video.
The development of IPv6 was necessitated by the rapid growth of the Internet of Things [IoT] and the depletion of IPv4 addresses.
Other reasons include inefficiencies in IPv4, such as slow processing and limited support for multimedia and security features.
Enhanced Security - IPv6 includes encryption and authentication options to ensure packet confidentiality and integrity.
Larger Address Space - With 128 bits, IPv6 offers a vastly larger address pool compared to IPv4's 32-bit addresses.
New Options and Extensions - IPv6 is designed to accommodate future technology and protocol extensions.
IPv6 addresses these challenges through the following key improvements:
Improved Header Format - IPv6 separates header options from the base header,
streamlining routing by reducing the need for routers to check most options.

IPv6 Addressing Methods

IPv6 employs three primary addressing methods:
Multicast - Identifies multiple hosts that share a multicast destination address, allowing a packet to be distributed to all associated interfaces.
Unicast - Identifies a single network interface. Packets sent to a unicast address are delivered to the designated interface.
Anycast - Identifies a group of interfaces, with packets delivered to the nearest available interface in the group.
Note: IPv6 does not support broadcast addressing, which was available in IPv4.

Types of IPv6 Addresses

IPv6 addresses are categorized based on their purpose, and the first few bits help identify the type of address:
Provider-Based Unicast Address - Used for global communication. The first 3 bits identify this type, followed by registry and provider IDs.
Geography-Based Unicast Address - Global routing is based on the geographical location, though not commonly in use.
Local Unicast Addresses Include:
Link-Local Addresses - Used for communication on the same link. These addresses begin with FE80 and are not forwarded by routers.
Site-Local Addresses - Equivalent to private IP addresses in IPv4, used for communication within an organization. They start with FEC0.

Special IPv6 Addresses

IPv4-Compatible Addresses - Allows IPv6 devices to communicate with IPv4 devices.
IPv4-Mapped Addresses - Allows IPv6 applications to represent IPv4 addresses.
Loopback Address - Used for testing internal communications on a device.
Unspecified Address - Used when a device is not assigned an IP address.

Advantages of IPv6

Real-time Data Transmission - IPv6 improves the speed and efficiency of real-time data transmission, such as live streaming with minimal delays.
Encryption - IPv6 can encrypt data at the network layer, even when application-layer encryption is not present.
Authentication - IPv6 supports authentication mechanisms to ensure data integrity.
Faster Routing - IPv6 reduces processing time at routers due to its fixed-size base header [40 bytes],
compared to IPv4’s variable header size [20-60 bytes].

Disadvantages of IPv6

Conversion Challenges - The transition from IPv4 to IPv6 requires significant effort and time due to differences in address structures.
Communication Barrier - IPv4 and IPv6 devices cannot communicate directly without transitional mechanisms.
Transition Period - The global transition from IPv4 to IPv6 will take time due to the widespread use of IPv4.
No Backward Compatibility - IPv6 is not backward compatible with IPv4, posing challenges in adoption.

Conclusion

IPv6 was developed in response to IPv4's limitations, such as address exhaustion and processing inefficiencies.
With a 128-bit address space, IPv6 offers vast addressing potential, improved security, and better support for modern network applications.
Despite the advantages, the transition to IPv6 faces challenges such as incompatibility with IPv4 and the need for global infrastructure updates.

MAC Addresses

Media Access Control [MAC] addresses are unique identifiers assigned to network interface cards [NICs] by their manufacturers.
They play a crucial role in communication within local network segments,
allowing devices to identify each other and ensure that data packets are transmitted to their intended recipients.

MAC Address Structure

A MAC address consists of 48 bits, typically displayed in hexadecimal format and separated by colons or hyphens [e.g., 01:23:45:67:89:AB].
The address can be divided into two parts:
Organizationally Unique Identifier [OUI] - The first 24 bits of a MAC address represent the OUI,
which is assigned to the device's manufacturer by the Institute of Electrical and Electronics Engineers [IEEE].
The OUI uniquely identifies the vendor of the network interface card.
Device Identifier - The remaining 24 bits are used by the manufacturer to assign a unique identifier to each network interface card they produce.
This ensures that every NIC has a distinct MAC address.

Finding the Vendor Using the MAC Address

To identify the vendor of a device based on its MAC address, you can use the OUI portion of the address.
By looking up the OUI in an online database or using a tool that has access to an updated OUI list,
you can determine which company manufactured the network interface card.
Here are a few methods to find the vendor using a MAC address:
IEEE OUI Lookup - The IEEE maintains an up-to-date list of OUI assignments, which can be accessed through their website.
By entering the OUI portion of the MAC address, you can retrieve information about the manufacturer.
Online MA - Address Lookup Tools, Several websites and online tools allow you to enter a MAC address and quickly retrieve information about the vendor.
Examples include Wireshark's OUI Lookup Tool and MAC Vendor Lookup.

The Essentials of Network

In today's world, where we rely heavily on the internet, there are several technical terms that we might encounter.
These terms might sound like jargon or alphabet soup to some people,
but they are actually important components that help our devices connect to the internet and communicate with each other.

Network Services

Let's start with DNS, which stands for Domain Name System.
Every website you visit has a unique IP address, which is a series of numbers that identifies the server where the website is hosted.
However, IP addresses can be difficult to remember, especially when there are millions of websites on the internet.
That's where DNS comes in. DNS translates human-readable domain names [like google.com] into IP addresses that computers can understand.
When you type a domain name into your web browser, your computer sends a DNS query to a DNS server, which responds with the IP address of the website you want to visit.
This allows your computer to connect to the correct server and load the website you requested.
In simpler terms, DNS acts as a phone book for the internet.
Just like how you look up a phone number in a phone book to call someone, your computer looks up a website's IP address in DNS to connect to it.

Moving on to DHCP, which stands for Dynamic Host Configuration Protocol.
DHCP is a protocol that automatically assigns IP addresses to devices on a network.
In the early days of networking, devices had to be manually configured with IP addresses, which was a time-consuming and error-prone process.
With DHCP, devices can automatically obtain an IP address from a DHCP server when they connect to a network.
This simplifies the process of setting up and managing a network, especially in large organizations with many devices.
To put it simply, DHCP assigns an IP address to your device when you connect to a network.
It's like checking into a hotel and being assigned a room number.
With DHCP, you don't have to manually configure your device's IP address every time you connect to a new network.

Finally, let's talk about ARP, which stands for Address Resolution Protocol.
ARP is a protocol that helps devices on a network find each other.
When a device wants to communicate with another device on the same network,
it needs to know the other device's MAC address, which is a unique identifier for the device's network interface.
However, devices typically only know each other's IP addresses, not their MAC addresses.
ARP allows a device to send a broadcast message on the network asking which device has a particular IP address.
The device with that IP address responds with its MAC address,
and the requesting device can then use that MAC address to communicate with the other device.
In simpler terms, ARP helps devices on a network find each other.
It's like asking a friend for someone's phone number so you can call or text them.

Port Numbers

In computer networking, a port is a communication endpoint that allows data to be exchanged between devices over a network.
There are many different types of ports, but in this chapter, we will focus on some of the most common ones, including SSH, HTTP, RDP, DHCP, and more.

First up is SSH, which stands for Secure Shell.
SSH is a secure protocol for accessing a remote computer over a network.
It uses encryption to protect the communication between the two devices,
making it a popular choice for system administrators and developers who need to access servers and other network devices remotely.
The default port for SSH is 22, but it can be changed to any other available port.

Next is HTTP, which stands for Hypertext Transfer Protocol.
HTTP is the foundation of the World Wide Web and is used to transfer web pages and other resources between servers and clients.
When you type a URL into your web browser, your computer sends an HTTP request to the server hosting the website,
which responds with the requested resource.
The default port for HTTP is 80, but it is often encrypted using HTTPS [HTTP Secure], which uses port 443.

RDP, or Remote Desktop Protocol, is a protocol used to access and control a remote computer.
It is commonly used by system administrators and support technicians to troubleshoot and fix issues on remote computers.
RDP uses port 3389 by default, but it is often used with a VPN [Virtual Private Network] to provide an extra layer of security.

DHCP, or Dynamic Host Configuration Protocol, is a protocol used to automatically assign IP addresses to devices on a network.
It simplifies the process of configuring network settings by allowing devices to obtain an IP address,
subnet mask, default gateway, and other network settings automatically.
DHCP uses ports 67 and 68 for communication between clients and servers.

SMTP, or Simple Mail Transfer Protocol, is a protocol used for sending email messages between servers.
When you send an email, your email client communicates with an SMTP server to send the message.
SMTP uses port 25 by default, but many email providers also support ports 465 and 587 for encrypted communication.

FTP, or File Transfer Protocol, is a protocol used for transferring files between servers and clients.
It is commonly used by web developers to upload and download files to and from web servers.
FTP uses ports 20 and 21 for communication, but it is often used with SSL/TLS [Secure Sockets Layer/Transport Layer Security] to encrypt the data being transferred.

These ports are commonly used for a variety of services such as web browsing, email, remote access, and database management.
It's important to note that these are just a few examples and there are many other ports used for different services.
Knowing which ports are used by different services is important for troubleshooting network issues,
securing your network, and understanding how different services communicate with each other.

Default Gateway vs. Router - Understanding the Difference

When it comes to computer networking, the terms "default gateway" and "router" are often used interchangeably, but they are not the same thing.
Understanding the difference between these two terms is important for anyone who wants to set up a network or troubleshoot network issues.
In this part, we'll explore what a default gateway is, what a router is, and how they differ from each other.

Default Gateway

A default gateway is an IP address on a network that serves as a route for all traffic that is not destined for a local network.
In other words, it's the address of the next hop that a device will send packets to if the destination IP address is not on the local network.
The default gateway is usually the IP address of the router that connects the local network to the internet.
For example, suppose you have a computer on a local network with an IP address of 192.168.1.10.
If the computer wants to send a packet to a website with an IP address of 192.168.2.10,
it will send the packet to the default gateway [i.e., the router], which will then forward the packet to the correct destination.

Router

A router is a device that connects two or more networks and routes traffic between them.
A router operates at the network layer [layer 3] of the OSI model and uses IP addresses to determine the next hop for each packet.
Routers can be physical devices, such as the ones provided by internet service providers [ISPs], or they can be virtual devices, such as software routers.
A router can perform a variety of functions, such as:
Routing traffic between networks.
Providing network address translation [NAT] to allow multiple devices to share a single public IP address.
Providing firewall and security features to protect the network.
Allocating IP addresses to devices on the network.

What's the Difference?

The main difference between a default gateway and a router is their function.
A default gateway is the IP address of the next hop for traffic that is not destined for a local network,
while a router is a device that connects two or more networks and routes traffic between them.
In other words, the default gateway is the address that a device uses to access the internet,
while a router is the device that makes that connection possible.
To summarize, a default gateway is a concept used within a local network to route traffic to the internet,
while a router is the device that connects multiple networks and routes traffic between them.
While these terms are often used interchangeably,
understanding their differences can help you troubleshoot network issues and optimize network performance.

TCP & UDP

What are TCP and UDP?

TCP [Transmission Control Protocol] and UDP [User Datagram Protocol] are both transport layer protocols
that are used to transmit data between devices.
TCP is a connection-oriented protocol, while UDP is a connectionless protocol.
In other words, when data is sent over TCP, a connection is established between the sender and receiver before data transmission can begin.
This connection ensures that data is transmitted in the correct order and that no data is lost during transmission.
With UDP, there is no connection established between the sender and receiver before data transmission.
Instead, data is sent as individual packets, with no guarantee that they will arrive in the correct order or that all packets will be received.

Key Differences Between TCP & UDP

One of the biggest differences between TCP and UDP is the way in which they handle data transmission.
TCP is a reliable protocol that guarantees that all data is transmitted and that it arrives in the correct order.
UDP, on the other hand, is an unreliable protocol that does not guarantee that all data will be transmitted or that it will arrive in the correct order.
Another key difference between TCP and UDP is the way in which they handle congestion.
TCP uses a congestion control mechanism that helps to ensure that the network is not overloaded with traffic.
UDP, on the other hand, does not have any congestion control mechanism and can send data at a much faster rate.

Advantages Of Using TCP

TCP is a reliable protocol that guarantees that all data is transmitted and that it arrives in the correct order.
This makes it ideal for applications where data integrity is critical, such as online banking or ecommerce websites.
TCP is also able to handle congestion in a way that helps to prevent network overload.
This is particularly important for applications that require a high degree of reliability, such as streaming video or online gaming.

Advantages Of Using UDP

UDP is a faster protocol than TCP, as it does not have the overhead of establishing a connection before data transmission can begin.
This makes it ideal for applications that require real-time data transmission, such as online voice and video chat.
UDP is also able to send data packets that are much larger than those sent by TCP,
which can be useful for applications that require the transfer of large files or datasets.

3-Way Handshake

The three-way handshake is a process used by computer networking protocols like TCP [Transmission Control Protocol]
to establish a connection between two devices before they start exchanging information.
The handshake involves three steps, which is why it's called the "three-way" handshake.
Here's how it works:

SYN [synchronize] packet - The process begins when one device [let's call it Device A] sends a SYN packet to the other device [Device B].
This packet is essentially Device A's way of saying "Hey, I want to talk to you. Can we establish a connection?"

SYN-ACK [synchronize-acknowledge] packet - When Device B receives the SYN packet, it responds with a SYN-ACK packet.
This packet lets Device A know that Device B has received the request and is willing to establish a connection.
The SYN-ACK packet contains a random sequence number that Device B generates,
as well as an acknowledgement number that lets Device A know which sequence number it's expecting to receive next.

ACK [acknowledge] packet - Finally, Device A sends an ACK packet back to Device B,
letting it know that it received the SYN-ACK packet and is ready to start exchanging information.
The ACK packet contains the sequence number generated by Device B in the previous step, plus one,
and another acknowledgement number that lets Device B know which sequence number it's expecting to receive next.
Once the three-way handshake is complete, the two devices have established a connection, and they can start exchanging information.

Think of it like a conversation between two people who have never met before.
Before they can start talking, they need to introduce themselves and make sure the other person is ready to talk.
The threeway handshake is like this introduction process for devices on a network.
In summary, the three-way handshake is a crucial process that allows devices to establish a connection with each other before exchanging information.
It's like the "hello" before a conversation, and it ensures that both devices are ready to start communicating.