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• Router: Connects different networks and routes traffic.
• Switch: Connects devices within the same network and uses MAC addresses to forward data.
• Hub: A basic device that connects multiple devices in a network (repeats data to all ports).
• Modem: Modulates and demodulates signals for Internet access.
• Access Point: Provides wireless connectivity to a wired network.
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• HTTP/HTTPS: Hypertext Transfer Protocol (Secure), used for web traffic.
• FTP: File Transfer Protocol, used for transferring files.
• SMTP: Simple Mail Transfer Protocol, used for sending emails.
• IMAP/POP3: Used for retrieving emails.
• DHCP: Dynamic Host Configuration Protocol, automatically assigns IP addresses.
• DNS: Resolves domain names to IP addresses.
• ARP: Maps IP addresses to MAC addresses.

• 802.11a: 5 GHz, 54 Mbps
• 802.11b: 2.4 GHz, 11 Mbps
• 802.11g: 2.4 GHz, 54 Mbps
• 802.11n: 2.4/5 GHz, up to 600 Mbps
• 802.11ac: 5 GHz, up to 3 Gbps
• 802.11ax (Wi-Fi 6): 2.4/5 GHz, up to 9.6 Gbps

• Firewall: Controls incoming and outgoing network traffic based on security rules.
• VPN: Securely connects to a remote network over the Internet.
• Encryption: Protects data by converting it into a secure format.
• Authentication: Verifies the identity of users/devices.
• IDS/IPS: Intrusion Detection/Prevention Systems monitor and prevent malicious activity.

• FTP: 20, 21
• Telnet: 23
• SMTP: 25
• DNS: 53
• HTTP: 80
• POP3: 110
• IMAP4: 143
• HTTPS: 443

OSI Model (Open Systems Interconnection Model)

The OSI model consists of seven layers that standardize network communication:

• Physical Layer: Handles the transmission of raw bit streams over physical media.
• Data Link Layer: Manages error detection, correction, and MAC addressing within a local network.
• Network Layer: Determines the best path for data and handles logical addressing (IP addresses).
• Transport Layer: Ensures reliable data transfer with error checking and flow control.
• Session Layer: Manages sessions and connections between applications.
• Presentation Layer: Translates data formats and handles encryption.
• Application Layer: Interfaces directly with user applications (e.g., web browsers, email clients).

An IP address is a unique identifier assigned to devices on a network to enable communication. IPv4 uses a 32-bit format (e.g., 192.168.1.1) and supports about 4.3 billion addresses, while IPv6 uses a 128-bit format (e.g., 2001:0db8::1) to accommodate a vastly larger number of devices.

IP addresses in IPv4 are divided into five classes (A, B, C, D, E) based on their leading bits. Here’s a breakdown of the most commonly used classes (A, B, C) along with their ranges:

1. Class A

   • Range: 1.0.0.0 to 126.255.255.255
   • Default Subnet Mask: 255.0.0.0
   • Purpose: Used for large networks with millions of devices.
   • Number of Networks: 128 (2^7 – 2 for reserved)
   • Hosts per Network: ~16.7 million (2^24 – 2 for network and broadcast addresses)

2. Class B

   • Range: 128.0.0.0 to 191.255.255.255
   • Default Subnet Mask: 255.255.0.0
   • Purpose: Medium-sized networks like those used by universities or businesses.
   • Number of Networks: 16,384 (2^14)
   • Hosts per Network: ~65,534 (2^16 – 2)
     
     

3. Class C

   • Range: 192.0.0.0 to 223.255.255.255
   • Default Subnet Mask: 255.255.255.0
   • Purpose: Small networks, commonly used for private or local business networks.
   • Number of Networks: ~2 million (2^21)
   • Hosts per Network: 254 (2^8 – 2)
     
     

4. Class D (Multicast)

   • Range: 224.0.0.0 to 239.255.255.255
   • Purpose: Reserved for multicast groups, not for host assignment.
     
     

5. Class E (Experimental)

   • Range: 240.0.0.0 to 255.255.255.255
   • Purpose: Reserved for research and experimental use, not for general public use.

Subnetting divides a larger network into smaller subnetworks, improving efficiency and security. The subnet mask determines how the IP address is split between the network and host portions.

• Example: In Class C, with a default subnet mask of 255.255.255.0, there’s only one subnet and 254 hosts.
  • By using a subnet mask of 255.255.255.192, you can create 4 subnets with 62 hosts each.

Benefits of Subnetting:

1. Efficient Use of IP Addresses: Avoid wasting IPs by dividing into subnets.
2. Improved Security: Isolate parts of the network.
3. Reduced Broadcast Traffic: Each subnet is its own broadcast domain.

A default gateway is the device (typically a router) that routes traffic from a local network to other networks, including the internet. It acts as an intermediary for devices to communicate outside their subnet.

• Example: If a device has an IP of 192.168.1.10 and a subnet mask of 255.255.255.0, its default gateway might be 192.168.1.1. This gateway routes traffic beyond the local 192.168.1.x network.