Table of contents
- Why do we need Computer Networks and how it all started?
- Explain Client-Server Architecture
- What are Protocols?
- How is data transferred over the internet?
- What does a data packet include?
- What is a Sequence number?
- What are IP Addresses?
- What are PORT numbers?
- What are Modems and Routers?
- What are LAN, WAN and MAN?
- Explain various topologies.
- Explain OSI Model
- Explain TCP/IP model
- Explain TCP / IP
- Difference between MAC and IP
- What is TCP and UDP
- What are Networking Devices?
- Protocols
Why do we need Computer Networks and how it all started?
Imagine a world without computer networks. In the early days of computing, each computer was like a separate island, isolated from the rest. If you wanted to share information between computers, you'd have to physically move data using things like floppy disks or tapes. This was incredibly inefficient and limited the potential of computers.
The need for computer networks emerged as computers became more common in various industries and institutions. Here are a few key reasons:
Resource Sharing: As computers became more powerful, it made sense to share their resources. Networks allow multiple users to access and use the same hardware, like printers or storage devices, simultaneously.
Remote Access: Networks enable users to access computers and data from remote locations. This was a game-changer for businesses with multiple branches or researchers collaborating across the globe.
Efficient Communication: Email and messaging systems were born out of networking, making communication faster and more convenient than traditional mail or phone calls.
Data Exchange: Networks made it possible to exchange data between computers seamlessly, which was crucial for fields like science and research.
Centralized Management: Networks allow for centralized management of resources and data, making it easier to maintain and secure information.
Internet Emergence: The development of the internet, which is essentially a massive global computer network, revolutionized how we access information, communicate, and conduct business.
Explain Client-Server Architecture
Client-server architecture is a fundamental concept in computer networking and software design. It describes the relationship between two types of computers or software components: clients and servers.
Clients are end-user devices or software applications that initiate requests, such as web browsers or email clients. They are user-focused and have interfaces for interaction.
Servers, on the other hand, are powerful computers or software programs designed to provide services or resources to clients. They respond to client requests efficiently and may not have a user interface.
Client-server interactions follow a request-response model, where clients send requests to servers, and servers process these requests and send back responses. This architecture is used in various applications, such as web browsing, email, and database management, and it allows for scalability and security measures to ensure authorized access.
What are Protocols?
Protocols are a set of rules or conventions that govern how data is transmitted and received between computers or devices on a network. Think of them as the 'language' that devices use to communicate effectively with each other. These rules ensure that data is sent, received, and interpreted correctly, enabling devices to understand and interact with one another on a network.
How is data transferred over the internet?
Step 1: Data Creation
- Data transfer begins with the creation of digital information. This could be anything from a simple text message, an email, a file, or even a video.
Step 2: Data Packaging (Encapsulation)
Before data can be sent over a network, it's organized and packaged into smaller units called data packets. Each packet typically includes:
The actual data (a part of the message or file).
Source and destination addresses (identifying where the data is coming from and where it's going).
Control information (such as error-checking codes and sequence numbers).
Step 3: Sending Data from the Source
The source device, often referred to as the sender or client, initiates the data transfer.
The data packets are sent from the source device to a network interface (like a network card) that connects it to the local network.
Step 4: Routing Within the Local Network
If the destination device is within the same local network as the source (e.g., devices connected to the same Wi-Fi router), the data packets are routed directly to the destination device using local addressing.
Actually, now your data packets will have private IP addresses so the NAT technology ensures that data packets leaving your private network have their source IP addresses and port numbers replaced with the public IP address of your router (ISP), allowing them to be routed across the broader internet. When responses come back, NAT maps them back to the appropriate internal device based on port numbers.
Step 5: Reaching the Destination Network
If the destination device is on a different network (e.g., a server on the internet), the data packets are sent to a local router or gateway.
The local router examines the destination address and determines the best path to reach the destination network.
Step 6: Data Transfer Across the Internet
The data packets are transmitted across the internet through a series of routers and switches.
Each router on the way examines the destination address and forwards the packets to the next hop until they reach a router in the destination network.
Step 7: Arrival at the Destination Network
- When the packets arrive at the destination network, they are further routed through local routers to reach the destination device.
Step 8: Reassembly at the Destination
- Once all the data packets have reached the destination device, they are reassembled in the correct order based on sequence numbers and other control information.
Step 9: Data Processing
- The destination device processes the received data. This could involve displaying a web page, storing a file, playing a video, or any other appropriate action based on the type of data received.
Step 10: Acknowledgment
- In many cases, the destination device sends acknowledgment packets back to the source to confirm the successful receipt of data.
What does a data packet include?
A data packet typically includes the source and destination IP addresses, source and destination port numbers, and sequence and acknowledgment numbers (for ordered and reliable delivery). These components work together to ensure data is correctly addressed, routed, and processed during transmission.
What is a Sequence number?
A "sequence number" is a unique identifier or serial number assigned to each data packet sent over a network. Sequence numbers serve several important purposes in network communication.
Packet Ordering
Detection of Missing or Duplicated Packets
Flow Control
What are IP Addresses?
IP addresses, short for "Internet Protocol addresses," are numerical labels assigned to every device connected to a computer network that uses the Internet Protocol for communication.
Here are some key points about IP addresses:
Unique Identifiers: IP addresses are used to uniquely identify devices on a network, just like a street address or a phone number uniquely identifies a physical location or a person.
Two Versions: There are two main versions of IP addresses in use today:
IPv4 (Internet Protocol version 4): This is the older version and uses a 32-bit address expressed as four sets of numbers separated by dots (e.g., 192.168.1.1). IPv4 addresses are running out due to the growth of the internet. There can be limited number of combination with this version
IPv6 (Internet Protocol version 6): IPv6 is the newer version designed to address the shortage of IPv4 addresses. It uses a 128-bit address format (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). IPv6 provides an almost unlimited number of unique addresses.
Hierarchical Structure: IP addresses are organized hierarchically. The address is typically divided into network and host portions.
The network portion identifies the specific network
The host portion identifies the individual device on that network.
Public vs. Private IP Addresses: Public IP addresses are used to identify devices on the global internet. Private IP addresses are used within private networks, like those in your home or office, and are not routable on the public internet. Network Address Translation (NAT) is used to map multiple private IP addresses to a single public IP address for internet access.
What are PORT numbers?
Definition:
Port numbers are 16-bit unsigned integers (ranging from 0 to 65535) used to identify specific communication endpoints in a network.
Key Points:
Port Types:
Well-Known Ports (0-1023): These are reserved for specific services and applications that are commonly used on the internet. For example, HTTP uses port 80, HTTPS uses port 443, and FTP uses port 21.
Registered Ports (1024-49151): These are assigned by the Internet Assigned Numbers Authority (IANA) to specific services or applications upon request. They are used by various applications and services but are not as universally recognized as well-known ports.
Dynamic or Private Ports (49152-65535): These ports are available for use by any application or service on an ad-hoc basis. They are often used for temporary or ephemeral communication.
Port Number Assignment:
Port numbers are assigned to both the source and destination devices in a network communication.
The combination of the source IP address, source port, destination IP address, and destination port uniquely identifies a network communication session.
Role in Networking:
Ports help devices distinguish between different services and applications running on the same device or remote devices.
When data packets arrive at a device, the port number is used to determine which application or service should handle the data.
Ports are essential for enabling multiple network services to coexist on a single device.
What are Modems and Routers?
Modem (Modulator-Demodulator):
A modem is a hardware device that serves as a bridge between a local network (such as your home or office network) and the wider internet. Its name is derived from its primary functions: modulation and demodulation.
Modems convert digital data from computers and other devices into analog signals for transmission over communication lines (such as telephone lines, cable TV lines, or fiber optic lines). They also demodulate incoming analog signals back into digital data.
The modem's main role is to establish the initial connection to the Internet Service Provider (ISP) and translate the incoming internet signal from the ISP into a format that devices in the local network can understand.
Modems may have Ethernet ports for connecting a single device directly via an Ethernet cable.
Router:
A router is a hardware device that manages the local network within a home or office and facilitates the distribution of internet connectivity to multiple devices.
Routers are responsible for assigning local IP addresses to devices within the network, performing Network Address Translation (NAT) to share a single public IP address provided by the ISP, and managing the flow of data between devices in the local network and the wider internet.
They serve as a central hub, allowing devices to connect to the internet either wirelessly (via Wi-Fi) or through wired connections (via Ethernet).
Routers are crucial for managing traffic within the local network and ensuring that data reaches its intended destinations efficiently.
In summary, modems establish the initial connection to the ISP and convert signals between digital and analog formats, while routers manage the local network, assign IP addresses, and facilitate internet distribution to multiple devices. Together, they enable internet connectivity for homes, offices, and other network environments.
What are LAN, WAN and MAN?
Certainly! When explaining LAN (Local Area Network), WAN (Wide Area Network), and MAN (Metropolitan Area Network) in an interview, you can provide concise definitions and highlight their key characteristics. Here's how you can define each network type:
LAN (Local Area Network):
A Local Area Network, or LAN, is a network that typically covers a small, localized area, such as a home, office, school, or single building.
LANs are designed for connecting devices within close proximity to each other, allowing them to share resources and communicate seamlessly.
Common LAN technologies include Ethernet (wired) and Wi-Fi (wireless).
LANs are often owned, controlled, and managed by a single organization, and they enable devices like computers, printers, and smartphones to connect and share data within the same physical location.
MAN (Metropolitan Area Network):
A Metropolitan Area Network, or MAN, is a network that spans a larger geographic area than a LAN but is still limited to a city or metropolitan region.
MANs are used to interconnect multiple LANs within a city, enabling high-speed data transfer over a wider coverage area.
Fiber optics is a common technology used in MANs for high-speed and reliable data transmission within a metropolitan area.
MANs can be owned and operated by a single organization or by multiple organizations collaborating to provide network services within a city.
WAN (Wide Area Network):
A Wide Area Network, or WAN, is a network that covers a vast geographic area, often spanning cities, countries, or continents.
WANs are designed for long-distance communication and connecting LANs and MANs over large geographical regions.
WANs enable global connectivity and data exchange, and they often use various technologies such as leased lines, satellite links, and the internet itself to connect distant locations.
WAN infrastructure is typically owned and operated by telecommunications companies or internet service providers (ISPs).
Explain various topologies.
Network topologies define the physical or logical layout of devices in a network and how they are interconnected. Each topology has its advantages and disadvantages, making it suitable for specific use cases. Here are some common network topologies:
Bus Topology:
In a bus topology, all devices are connected to a single central cable or "bus." The cable acts as the communication backbone.
Each device on the bus receives all data transmissions but only processes the data intended for it, based on its unique address.
Pros: Simple and inexpensive to set up, suitable for small networks.
Cons: Susceptible to cable failures; network performance degrades as more devices are added.
Ring Topology:
In a ring topology, each device is connected to exactly two other devices, forming a closed loop or ring.
Data travels in one direction around the ring until it reaches its destination.
Pros: Even data distribution, predictable and consistent performance.
Cons: If one device or cable in the ring fails, the entire network can be disrupted.
Star Topology:
In a star topology, all devices are connected to a central hub or switch. Each device has a dedicated connection to the central point.
Data transmissions between devices are routed through the central hub or switch.
Pros: Easy to set up and manage, failure of one device does not affect others, scalable.
Cons: Relies heavily on the central hub; if it fails, the entire network goes down.
Tree Topology:
A tree topology combines characteristics of both star and bus topologies.
Devices are arranged in hierarchies, with multiple star-configured networks connected to a central bus.
Pros: Scalable, can cover a wide area, redundant paths can improve reliability.
Cons: Complex to set up and manage, costly, failure of central bus impacts the entire network.
Mesh Topology:
In a mesh topology, every device is connected to every other device, creating multiple direct paths for data transmission.
Full mesh means every device is connected to every other device, while partial mesh has some devices interconnected.
Pros: Robust, fault-tolerant (if one link fails, alternative paths are available), highly reliable.
Cons: Complex and costly to set up (especially full mesh), many cables and connections required.
Explain OSI Model
The OSI model, which stands for the Open Systems Interconnection model, is a conceptual framework used to understand how network communication works.
Number of Layers:
- Mention that the OSI model is divided into seven layers.
The function of Each Layer:
Physical Layer: Deals with the physical hardware, cables, and transmission of raw binary data.
Data Link Layer: Ensures reliable data transfer within a local network and handles MAC addresses.
Network Layer: Manages addressing and routing, using IP addresses and routers.
Transport Layer: Ensures reliable end-to-end communication using protocols like TCP and UDP.
Session Layer: Manages communication sessions and synchronization.
Presentation Layer: Handles data translation, encryption, and compression.
Application Layer: Provides user interfaces and network services for applications.
Analogy👇:
Imagine the OSI Model as Sending a Letter:
Physical Layer - Writing the Letter:
- The Physical Layer is like writing a letter on a piece of paper. It's the raw content of your message.
Data Link Layer - Enveloping the Letter:
- The Data Link Layer is similar to placing your letter inside an envelope. It adds a protective layer around the content.
Network Layer - Addressing the Envelope:
- The Network Layer is equivalent to addressing the envelope with the recipient's name and address. It determines where the letter needs to go.
Transport Layer - Selecting a Postal Service:
- The Transport Layer is like choosing the postal service or courier to send your letter. It ensures the reliable delivery of the envelope.
Session Layer - Planning the Delivery Route:
- The Session Layer is akin to planning the route the postal service will take to reach the destination. It ensures the letter follows the right path.
Presentation Layer - Language Translation:
- The Presentation Layer is like a translator who ensures that the recipient can read and understand the letter, even if they speak a different language.
Application Layer - Sending the Letter:
- Finally, the Application Layer is the act of sending the letter through a mailbox or post office. It's the user's interaction with the entire process.
Explain TCP/IP model
Provide a brief description of each layer and its main functions:
Network Interface Layer (Link Layer):
Mention that this layer deals with physical connections and includes hardware components like network interface cards (NICs) and protocols like Ethernet and Wi-Fi.
Explain that it's responsible for transmitting raw binary data over the physical medium.
Internet Layer:
Describe this layer as being responsible for addressing, routing, and forwarding data packets between devices on different networks.
Mention that it uses IP addresses and routers to make routing decisions.
Transport Layer:
Explain that the Transport Layer ensures reliable end-to-end communication between devices.
Mention that it uses protocols like TCP (reliable) and UDP (unreliable) and handles tasks like error checking and data sequencing.
Application Layer:
Describe the Application Layer as where applications and user interactions occur.
Mention that it includes protocols like HTTP (for web browsing), FTP (for file transfer), and SMTP (for email).
Explain TCP / IP
The TCP/IP model, named after the two core protocols it's based on, is a fundamental framework for understanding how network communication works
Physical Layer - Writing the Letter:
- The Physical Layer is like writing a letter on a piece of paper. It's the raw content of your message.
Data Link Layer - Enveloping the Letter:
- The Data Link Layer is similar to placing your letter inside an envelope. It adds a protective layer around the content.
Network Layer - Addressing the Envelope:
- The Network Layer is equivalent to addressing the envelope with the recipient's name and address. It determines where the letter needs to go.
Transport Layer - Selecting a Postal Service:
- The Transport Layer is like choosing the postal service or courier to send your letter. It ensures the reliable delivery of the envelope.
Session Layer - Planning the Delivery Route:
- The Session Layer is akin to planning the route the postal service will take to reach the destination. It ensures the letter follows the right path.
Presentation Layer - Language Translation:
- The Presentation Layer is like a translator who ensures that the recipient can read and understand the letter, even if they speak a different language.
Application Layer - Sending the Letter:
- Finally, the Application Layer is the act of sending the letter through a mailbox or post office. It's the user's interaction with the entire process.
Difference between MAC and IP
1. IP Addresses (Layer 3 - Network Layer):
IP addresses are logical addresses used for routing data between devices across different networks, including the Internet.
They are globally significant and help devices find their way through complex, interconnected networks.
IP addresses are hierarchical, and routers use them to determine the path data should take to reach its destination.
2. MAC Addresses (Layer 2 - Data Link Layer):
MAC addresses are physical addresses associated with network interface cards (NICs) and other hardware components. They are unique identifiers assigned to each NIC.
They are used for communication within the same local network (e.g., a LAN segment).
MAC addresses are essential for local network communication, such as delivering data packets between devices within the same LAN.
What is TCP and UDP
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are two transport layer protocols used in networking.
TCP (Transmission Control Protocol):
Connection-Oriented: It's like making a phone call; you establish a connection before talking.
Reliable: Ensures your message arrives in order and accurately, like a registered letter.
Flow Control: Adjusts the speed of talking to avoid overwhelming the listener.
Connection State: Keeps track of the conversation's progress, just like remembering what you said.
Used for: Sending important data, like emails, files, or web pages.
UDP (User Datagram Protocol):
Connectionless: Similar to sending a letter without calling first; no initial setup.
Unreliable: Like sending a postcard; you hope it arrives, but there are no guarantees.
No Flow Control: Sends at a constant rate, regardless of how fast or slow the other side can handle.
No Connection State: Doesn't remember what was said previously; each message is separate.
Used for: Real-time stuff, like live video, online gaming, or quick data requests.
Differences:
TCP is like a phone call, while UDP is like sending postcards.
TCP ensures your message is received correctly, while UDP doesn't guarantee that.
TCP adjusts the speed of talking (flow control); UDP talks at a constant pace.
TCP remembers the conversation's progress; UDP treats each message separately.
Choose TCP when reliability is vital; pick UDP for speed and real-time applications.
What are Networking Devices?
Networking devices are hardware components or equipment used to facilitate communication and data exchange within computer networks. These devices serve various purposes and play essential roles in network design and management. Here's an explanation of some common networking devices:
1. Router:
A router is a critical networking device that connects multiple networks and directs data packets between them.
It makes decisions based on IP addresses to forward data to its intended destination.
Routers are essential for connecting a local network to the internet.
2. Switch:
A switch is used to connect multiple devices within the same local network (e.g., computers, printers) and efficiently manage data traffic.
It operates at the Data Link Layer (Layer 2) of the OSI model and uses MAC addresses for packet forwarding.
3. Access Point (AP):
An access point is a device that allows wireless devices (such as laptops and smartphones) to connect to a wired network using Wi-Fi.
Access points are commonly used in Wi-Fi networks to provide wireless connectivity.
4. Modem (Modulator-Demodulator):
A modem converts digital data from a computer into analog signals for transmission over analog communication lines (e.g., phone lines or cable TV lines).
It also demodulates incoming analog signals back into digital data for the receiving computer.
5. Firewall:
A firewall is a security device or software that protects a network from unauthorized access and cyber threats.
It can filter incoming and outgoing network traffic based on predefined rules and policies.
6. Hub:
Hubs are now considered outdated but were once used to connect multiple devices within a network.
They operate at the Physical Layer (Layer 1) and simply broadcast incoming data to all connected devices.
7. Bridge:
A bridge connects and filters traffic between two or more network segments to reduce network congestion and improve efficiency.
It operates at the Data Link Layer (Layer 2).
8. Gateway:
A gateway is a device or software component that connects two different networks with different communication protocols.
It acts as a translator to enable data transfer between the networks.
9. Load Balancer:
Load balancers distribute network traffic evenly across multiple servers or resources to ensure efficient resource utilization and high availability.
They are commonly used in data centers and web services.
10. Proxy Server:
A proxy server acts as an intermediary between client devices and the internet.
It can enhance security, provide caching, and help control access to web resources.
11. Network Attached Storage (NAS):
- NAS devices are dedicated file storage devices connected to a network, providing centralized file storage and sharing capabilities.
Protocols
Protocols are a set of rules and conventions that govern how data is transmitted and received over a computer network. They ensure that devices within a network can communicate effectively by defining standards for data formatting, error checking, addressing, and more. Here's an overview of some common networking protocols:
1. TCP/IP (Transmission Control Protocol/Internet Protocol):
TCP/IP is a suite of protocols that underlies the internet and most modern networks.
TCP (Transmission Control Protocol) ensures reliable, connection-oriented communication, while IP (Internet Protocol) handles addressing and routing.
2. HTTP (Hypertext Transfer Protocol):
HTTP is the protocol used for transmitting web pages and data on the World Wide Web.
It defines how web browsers request and receive web content from web servers.
3. HTTPS (Hypertext Transfer Protocol Secure):
- HTTPS is a secure version of HTTP that uses encryption (SSL/TLS) to protect the confidentiality and integrity of data transmitted between a web browser and a server.
4. FTP (File Transfer Protocol):
FTP is a protocol for transferring files between computers on a network.
It provides methods for uploading, downloading, and managing files on remote servers.
5. SMTP (Simple Mail Transfer Protocol):
SMTP is used for sending email messages between email servers.
It defines how email clients and servers communicate to deliver messages.
6. POP3 (Post Office Protocol 3) and IMAP (Internet Message Access Protocol):
These protocols are used by email clients to retrieve messages from email servers.
POP3 downloads messages to the client, while IMAP allows messages to be managed on the server.
7. DNS (Domain Name System):
DNS is a protocol used to translate human-readable domain names (e.g., example.com) into IP addresses.
It plays a crucial role in navigating the internet by resolving domain names to their corresponding IP addresses.
8. DHCP (Dynamic Host Configuration Protocol):
DHCP is used to automatically assign IP addresses and network configuration parameters to devices on a network.
It simplifies network management by dynamically allocating addresses.
9. SSH (Secure Shell):
SSH is a protocol used for secure remote access and secure file transfer over an insecure network.
It provides encrypted communication between a client and a server.
10. Telnet:
Telnet is an older protocol used for remote terminal access to network devices.
It transmits data in plaintext, making it less secure than SSH.
11. SNMP (Simple Network Management Protocol):
SNMP is used for managing and monitoring network devices, such as routers, switches, and servers.
It allows administrators to collect information and configure network equipment remotely.
12. ICMP (Internet Control Message Protocol):
ICMP is used for diagnostic and error-reporting purposes in IP networks.
It includes functions like ping and traceroute to check network connectivity and troubleshoot issues.
13. BGP (Border Gateway Protocol):
BGP is a routing protocol used in the internet to exchange routing and reachability information between autonomous systems (ASes).
It's essential for routing traffic between different parts of the internet.