Network Examples and Protocols Exercise Solutions | KalviGavani

(a) FTP    (b) SMTP    (c) HTTP    (d) POP3

(a) 80    (b) 21    (c) 25    (d) 110

(a) POP3    (b) SMTP    (c) IMAP    (d) FTP

(a) UDP    (b) TCP    (c) IP    (d) ICMP

(a) 16    (b) 32    (c) 64    (d) 128

(a) HTTP    (b) HTTPS    (c) FTP    (d) Telnet

(a) File transfer    (b) Email    (c) Video streaming    (d) Web browsing

(a) Class A    (b) Class B    (c) Class C    (d) Class D

(a) 255.0.0.0    (b) 255.255.0.0    (c) 255.255.255.0    (d) 255.255.255.255

(a) 25 and 110    (b) 20 and 21    (c) 80 and 443    (d) 53 and 67

HTTPS is HTTP + SSL/TLS encryption, making it essential for any site that handles sensitive data like passwords or credit card numbers.

An IP address is a unique numerical identifier assigned to each device on a network for communication.

IPv4:

• 32-bit address, written in dotted-decimal notation (e.g., 192.168.1.1).
• Four octets, each ranging from 0 to 255.
• Approximately 4.3 billion unique addresses.
• Classes: A (large networks), B (medium), C (small), D (multicast), E (reserved).

IPv6:

• 128-bit address, written in hexadecimal (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).
• Eight groups of four hexadecimal digits separated by colons.
• Virtually unlimited addresses (3.4 x 10^38).
• Built-in security (IPsec), better multicast, and auto-configuration.

Subnetting is the practice of dividing a large network into smaller sub-networks (subnets) for better management, security, and performance.

Subnet mask determines which part of an IP address is the network portion and which is the host portion.

Example: For IP 192.168.1.100 with subnet mask 255.255.255.0 (/24):

• Network portion: 192.168.1.0
• Host portion: 0.0.0.100
• Usable host range: 192.168.1.1 to 192.168.1.254
• Broadcast address: 192.168.1.255
• Maximum hosts: 254 (256 - 2 for network and broadcast)

Benefits of subnetting:

• Reduces network congestion by limiting broadcast domains.
• Improves security by isolating network segments.
• Efficient use of IP addresses.

A domain name is a human-readable address used to access websites (e.g., www.google.com). It maps to a numeric IP address through the Domain Name System (DNS).

How it works: 1. User types www.example.com in the browser. 2. The browser queries a DNS server to resolve the domain name. 3. DNS returns the IP address (e.g., 93.184.216.34). 4. The browser connects to that IP address to load the website.

Structure of a domain name:

• Top-Level Domain (TLD): .com, .org, .in, .edu
• Second-Level Domain: example
• Subdomain: www
• Full: www.example.com

Domain names are easier to remember than IP addresses, which is why DNS exists to translate between them.

HTTP (HyperText Transfer Protocol):

• Purpose: Transfers web pages and resources between a web server and a browser.
• Port: 80 (HTTP), 443 (HTTPS).
• Stateless: Each request is independent; the server doesn't remember previous requests.
• Methods: GET (retrieve), POST (submit), PUT (update), DELETE (remove).
• Example: When you visit a website, your browser sends an HTTP GET request, and the server responds with the HTML page.

FTP (File Transfer Protocol):

• Purpose: Transfers files between a client and a server.
• Ports: 21 (control), 20 (data).
• Modes: Active and Passive.
• Commands: PUT (upload), GET (download), DELETE, RENAME.
• Example: Uploading website files to a hosting server using FileZilla.

SMTP (Simple Mail Transfer Protocol):

• Purpose: Sends emails from a client to a mail server or between mail servers.
• Port: 25 (standard), 587 (submission), 465 (SMTP over SSL).
• Push protocol: It pushes emails to the receiving server.
• Example: When you click "Send" in Gmail, SMTP transfers your email to the recipient's mail server.

POP3 (Post Office Protocol version 3):

• Purpose: Downloads emails from a mail server to a local client.
• Port: 110 (standard), 995 (over SSL).
• Downloads and deletes: By default, emails are removed from the server after download.
• Example: Downloading emails to Outlook on a single computer.

IMAP (Internet Message Access Protocol):

• Purpose: Accesses and manages emails on the server without downloading.
• Port: 143 (standard), 993 (over SSL).
• Server-based: Emails stay on the server; multiple devices can access the same mailbox.
• Example: Reading Gmail on both your phone and computer with synced read/unread status.

IP Address Classes (IPv4):

Private IP Address Ranges (not routable on the Internet):

Private IPs are used within local networks (homes, offices) and translated to public IPs via NAT.

Subnet Mask:

• Determines the network and host portions of an IP address.
• Example: IP 192.168.1.50 with mask 255.255.255.0
• Network: 192.168.1.0
• Host: 50
• Broadcast: 192.168.1.255
• Usable hosts: 192.168.1.1 to 192.168.1.254 (254 hosts)

TCP Use Cases:

• Web browsing (HTTP/HTTPS)
• Email (SMTP, IMAP, POP3)
• File transfer (FTP)
• SSH (secure remote access)
• Any application where data integrity matters more than speed.

UDP Use Cases:

• Video streaming (YouTube, Netflix)
• Online gaming (real-time updates)
• DNS queries (quick lookups)
• VoIP (Skype, WhatsApp calls)
• Any application where speed matters more than perfect delivery.

TCP 3-Way Handshake: 1. Client sends SYN (synchronise). 2. Server responds with SYN-ACK (synchronise-acknowledge). 3. Client sends ACK (acknowledge). Connection is now established.

IPv4 Addressing:

• 32-bit address divided into 4 octets.
• Written in decimal: 192.168.1.1
• Each octet: 0–255 (8 bits each).
• Total addresses: 2^32 = ~4.3 billion.
• Example: 172.16.254.1

IPv6 Addressing:

• 128-bit address divided into 8 groups of 4 hexadecimal digits.
• Written in hexadecimal: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
• Can be abbreviated: 2001:db8:85a3::8a2e:370:7334
• Total addresses: 2^128 = 3.4 x 10^38 (virtually unlimited).
• Example: ::1 (loopback), fe80::1%eth0 (link-local).

Why IPv6 was needed: 1. Address exhaustion — IPv4's 4.3 billion addresses are depleted due to Internet growth. 2. No more NAT — IPv6 provides enough addresses for every device to have a public IP. 3. Built-in security — IPsec is mandatory in IPv6. 4. Simplified header — IPv6 headers are simpler, improving router performance. 5. Auto-configuration — Devices can generate their own IPv6 addresses. 6. Better multicast — IPv6 has improved multicast and quality of service features.

IPv4 vs IPv6 Comparison:

SMTP (Simple Mail Transfer Protocol) is responsible for sending emails from a client to a mail server and between mail servers.

Email flow using SMTP:

1. Sender's email client (e.g., Outlook, Gmail web) composes an email and sends it to the sender's SMTP server. 2. The sender's SMTP server looks up the recipient's domain (e.g., gmail.com) in DNS to find the recipient's SMTP server (MX record). 3. The sender's SMTP server transfers the email to the recipient's SMTP server using SMTP. 4. The recipient's SMTP server stores the email in the recipient's mailbox. 5. The recipient retrieves the email using POP3 or IMAP.

Key SMTP commands:

• HELO/EHLO — identifies the client to the server.
• MAIL FROM — specifies the sender's email address.
• RCPT TO — specifies the recipient's email address.
• DATA — begins the email content.
• QUIT — ends the SMTP session.

Important distinction: SMTP is only for sending emails. POP3 and IMAP are for receiving/accessing emails. Together, they form the complete email system.