The OSI (Open Systems Interconnection) Model is a conceptual framework that standardizes the functions of a network communication system by dividing it into seven distinct layers. These layers ensure seamless communication between different systems and networks by defining protocols and packet transfer processes.

Difference Between OSI and TCP/IP Model:

Difference between HTTP and HTTPS

• Meaning: HTTP = HyperText Transfer Protocol, HTTPS = HyperText Transfer Protocol Secure.
• Security: HTTP is not encrypted, HTTPS is encrypted using SSL/TLS.
• Data Protection: HTTP data can be intercepted, HTTPS protects against eavesdropping and tampering.
• Port: HTTP uses port 80, HTTPS uses port 443.
• Certificate: HTTP does not require a certificate, HTTPS requires a digital certificate.

Subnet Mask

A subnet mask is a 32-bit number used to divide an IP address into network and host portions. It helps determine which part of the IP address identifies the network and which part identifies the device within that network.

Example: 255.255.255.0

Localhost IP Address

The localhost IP address refers to the local machine itself. It is used to test network applications on the same device.

Localhost IPv4: 127.0.0.1

NAT (Network Address Translation)

NAT is a networking technique that allows multiple private IP addresses within a local network to share a single public IP address for Internet access. It helps conserve public IP addresses and improves network security.

Ransomware

Ransomware is a type of malicious software that encrypts a victim’s data and demands a ransom payment to restore access. It often spreads through phishing emails, malicious links, or infected downloads.

Firewall

A firewall is a network security system that monitors and controls incoming and outgoing traffic based on predefined security rules. It acts as a barrier between trusted internal networks and untrusted external networks.

Why ping fails (from the diagram)

• Wrong IP subnet: Mask 255.255.255.240 = /28 (block size 16). Host A = 192.168.1.20 belongs to network 192.168.1.16/28 (range 16–31). Host B = 192.168.1.201 belongs to network 192.168.1.192/28 (range 192–207). They are in different subnets, so direct communication fails without a router.
• Cable type issue (possible): Two PCs directly connected usually need a crossover cable (unless NIC supports Auto MDI/MDIX). Using straight-through may cause no physical link on some devices.

What can be done to provide connectivity

• Option 1 (Best for direct link): Put both hosts in the same subnet
  Example (keep /28): Set Host B to 192.168.1.21 with mask 255.255.255.240 (or any IP within 192.168.1.17–192.168.1.30). Then both are in 192.168.1.16/28.
• Option 2: Use a router (if different subnets must remain)
  Connect both to a router (or L3 switch), configure routing, and set correct default gateway on both hosts.
• Option 3 (Physical fix): Use correct Layer-1 connection
  Use a crossover cable OR connect both hosts to a switch using straight-through cables (or ensure Auto MDI/MDIX is enabled).

How to identify the problem (troubleshooting reasons)

• Check physical link: Link LEDs should be ON; if OFF, suspect wrong cable/port/speed-duplex.
• Verify IP settings: Check IP & mask on both hosts (ipconfig/ifconfig). Compute network IDs to see if they match.
• Ping tests: Ping 127.0.0.1 (TCP/IP stack), then ping own IP, then ping the other host.
• Check ARP: If same subnet, ARP table should show the other host’s MAC; if not appearing, subnet/cable issue likely.
• ICMP blocking: Check host firewall settings that may block ping (ICMP).

Problem: A utility is installed but does not start automatically when the computer boots.

Solution:

• Add the utility to the Startup programs so it runs automatically at system boot.
• In Windows, this can be done by:
  • Placing the utility shortcut in the Startup folder, or
  • Enabling it from Task Manager → Startup tab.
• Ensure the utility is not disabled in startup settings.

Conclusion: Configuring the application to run at startup will solve the issue.

i. Printing a document: Ctrl + P

ii. PowerPoint slide show
Start slideshow: F5 (from beginning)
Exit slideshow: Esc

iii. Increase font size: Ctrl + Shift + >

IPv6 (Internet Protocol version 6) is the latest version of the Internet Protocol used to identify devices on a network. It uses a 128-bit address format, allowing a very large number of unique IP addresses.

Why IPv6 is Needed

• IPv4 address space is almost exhausted.
• IPv6 provides a much larger address space.
• Improves security with built-in IPsec support.
• Supports better routing and network efficiency.

Multiplexing

Multiplexing is a technique used in data communication to combine multiple signals and transmit them over a single communication channel to improve bandwidth utilization.

Types of Multiplexing

• Frequency Division Multiplexing (FDM): Divides the available bandwidth into multiple frequency bands; each signal uses a different frequency.
• Time Division Multiplexing (TDM): Shares the channel by allocating different time slots to different signals.
• Wavelength Division Multiplexing (WDM): Used in fiber optics; multiple signals are sent using different light wavelengths.
• Code Division Multiplexing (CDM): Multiple signals share the same channel using unique codes.

Connection Types in Networking

i. Router to Router:
Uses a Crossover Cable because both devices transmit and receive on the same pins.

ii. Router to Switch:
Uses a Straight-Through Cable because router and switch use different transmit/receive pins.

iii. Computer to Computer:
Uses a Crossover Cable for direct communication without an intermediate device.

iv. Hub to Switch:
Uses a Crossover Cable since both are similar networking devices.

A computer virus is a malicious software program designed to harm or disrupt the normal functioning of a computer. It can replicate itself and spread to other devices, damaging data, files, or software.

Examples of antivirus software:

1. Norton
2. McAfee
3. Kaspersky
4. Avast
5. Bitdefender
6. Panda