Section 1: What Is an IP Address?

Goal: Understand what IPs are and why they matter.

1. What’s an IP Address?

Think of an IP address as a house address for devices (PCs, phones, routers). It tells them where to send or receive data.

IPv4 uses 32 bits, written as 4 numbers (e.g., 192.168.1.1). Each number (0-255) is an octet (8 bits).

Example: Your laptop might be 192.168.1.10, talking to your router at 192.168.1.1.

2. Why Do We Need It?

Devices use IPs to find each other, like how you need a friend’s address to send a letter.

Problem: IPv4 has only 4.3 billion addresses (2³²), and many are reserved, so we’re running low (hello, IPv6!).

Formula: Total IPs = 2³² = 4,294,967,296

Section 2: IP Classes (Public and Private)

Goal: Learn how IPs are grouped and the difference between public and private.

1. What Are IP Classes?

IPv4 divides IPs into 5 classes (A, B, C, D, E) based on the first octet. Each has a default size for networks and hosts (devices).

Note: 127.0.0.0/8 is loopback (e.g., 127.0.0.1 tests your device).

2. Public vs. Private IPs

Public: Unique worldwide, routable on the internet (e.g., 8.8.8.8 - Google DNS).

Private: Local only, reused in different networks (e.g., 192.168.1.1 at your home and mine).

Explanation:

• Class A: /8 = 24 host bits → 2²⁴ - 2 = 16,777,214. Min = 10.0.0.1, Max = 10.255.255.254.
• Class B: /16 = 16 host bits → 2¹⁶ - 2 = 65,534. Min = 172.16.0.1, Max = 172.31.255.254.
• Class C: /24 = 8 host bits → 2⁸ - 2 = 254. Min = 192.168.0.1, Max = 192.168.255.254 (each /24 ends at .254).

Formula: Usable Hosts = 2^(32 - Mask) - 2

Section 3: Subnetting and CIDR (Breaking It Down)

Goal: Learn how to split or combine networks, step-by-step.

1. What’s Subnetting?

It’s like chopping a big cake into smaller slices. You take one network (e.g., 192.168.0.0/24) and make smaller ones (e.g., /26).

Why? Organize devices (e.g., IT vs. HR), improve security, reduce traffic.

2. Subnetting Step-by-Step

Start: 192.168.0.0/24 (254 usable hosts).

Goal: 4 subnets.

1. How Many Subnets? Need 4 → 2² = 4, so borrow 2 bits.
2. New Mask: /24 + 2 = /26.
3. Host Bits Left: 32 - 26 = 6.
4. Total IPs per Subnet: 2⁶ = 64.
5. Usable Hosts: 64 - 2 = 62.
6. Ranges:

Subnet 0 Explained: Old systems skipped it (confused with network address), but it’s usable now.

3. CIDR (Flexible Sizing)

CIDR lets you pick any mask (e.g., /23) instead of fixed /8, /16, /24.

Example: 192.168.0.0/23 = 510 hosts (2⁹ - 2).

4. Supernetting (e.g., 192.168.0.0/21 to /16)

Combines smaller networks into a big one.

• /21: Mask: 255.255.248.0, Hosts: 2¹¹ - 2 = 2046, Range: 192.168.0.0 - 192.168.7.255 (usable: .0.1 - .7.254). Use: 1000 devices (school).
• /16: Mask: 255.255.0.0, Hosts: 2¹⁶ - 2 = 65,534, Range: 192.168.0.0 - 192.168.255.255 (usable: .0.1 - .255.254). Use: University.

Formulas: Subnets = 2ᴮ (B = borrowed bits), Hosts = 2^(32 - Mask) - 2

5. Common Subnets

Section 4: VLANs vs. Subnets

Goal: Understand VLANs, how they differ from subnets, and why they’re used.

1. What’s a VLAN?

A VLAN is like separate rooms in a house, but all on one switch. It groups devices without needing extra cables or routers.

Uses tags (VLAN IDs) to mark traffic.

2. VLANs vs. Subnets

3. Why VLANs Over Subnets?

• Security: Guests (VLAN 30) can’t see Servers (VLAN 40).
• Less Chaos: Cuts broadcast traffic (e.g., ARP floods).
• Easier: Move a PC to VLAN 20 without changing its IP.

4. 4 VLAN Example

Why It Matters: Keeps Guests out of Servers, reduces network noise, fits all in one /24.

5. Configuring VLANs

FortiGate (Router)

Cisco Switch

D-Link Switch

MikroTik

pfSense

Formula: VLANs don’t change IP math—use Subnet formulas (Hosts = 2^(32 - Mask) - 2)

Section 5: NAT and PAT (Getting Online)

Goal: Learn how private IPs connect to the internet.

1. What’s NAT?

NAT is like a translator—it changes your private IP (e.g., 192.168.1.10) to a public IP (e.g., 203.0.113.1) so you can browse the web.

Types:

• Static NAT: 1 private IP → 1 public IP (e.g., a server).
• Dynamic NAT: Many private IPs → a pool of public IPs.
• PAT (Port Address Translation): Many private IPs → 1 public IP using ports.

2. PAT Explained

PAT is a special NAT that adds port numbers to squeeze lots of devices into one public IP.

How It Works:

• Laptop (192.168.1.10:12345) → Router (203.0.113.1:54321).
• Phone (192.168.1.11:56789) → Router (203.0.113.1:98765).

Real-World: Your home WiFi—10 devices share 1 public IP via PAT.

3. Configuring NAT/PAT

FortiGate

Cisco

MikroTik

pfSense

Formula: PAT Ports = 2¹⁶ = 65,536 per public IP

Section 6: Multicast and Experimental IPs

Goal: Understand special IPs for group messaging and testing.

1. Multicast (Class D)

Range: 224.0.0.0 - 239.255.255.255.

Sends data to many devices at once (e.g., live TV).

Examples: 224.0.0.1 (all local devices), 239.255.255.250 (smart TVs).

2. Experimental (Class E)

Range: 240.0.0.0 - 255.255.255.255.

For research, not internet-ready.

Formula: No host calc—fixed ranges

Section 7: Dynamic IP to Static IP

Goal: Make a changing IP act like a fixed one.

1. Tools

• No-IP: Free DDNS (e.g., myhome.no-ip.com).
• Cloudflare Zero Trust: Secure tunneling.
• DynDNS: DDNS with domains.

2. Configs

FortiGate

Cisco

MikroTik

pfSense

3. Better Protocols

Formula: No math—just config steps

Section 8: Advanced IPv4 Topics

Goal: Explore extra tools and concepts.

• IP Fragmentation: Splits big packets (e.g., 4000 bytes → 1500-byte chunks).
• IPv4 Header: Contains Source IP, Destination IP, TTL (hops).
• ARP: Links IPs to MAC (e.g., 192.168.1.1 → router’s MAC).
• DHCP: Auto-assigns IPs (e.g., 192.168.1.100 - .150). FortiGate: Network > Interfaces > LAN, Enable DHCP.
• Default Gateway: Exit point (e.g., 192.168.1.1 to internet).
• QoS: Prioritizes traffic (e.g., VoIP over downloads).

Formula: No specific math—concept-based

Section 9: IP-to-IP Routing and Virtual IPs

Goal: Understand how packets travel and why VIPs work.

1. IP-to-IP Routing

Packets hop from IP to IP via routers using tables (e.g., “192.168.2.0/24 go to 203.0.113.1”).

2. Virtual IPs (VIPs)

Why Gateway IP? The public IP (e.g., 203.0.113.1) is what outsiders see; VIP maps it to private (e.g., 192.168.1.10).

FortiGate: Virtual IPs > New, External = WAN IP.

Formula: No math—routing logic

Section 10: Buying and Routing ICANN IPs

Goal: Get and use your own public IPs.

1. How to Buy

Go to an RIR (e.g., ARIN.net). Pay ($500 + $150/year for /24, e.g., 203.0.114.0/24).

2. Routing

Use BGP with your ISP or cloud (e.g., AWS) to announce IPs.

Formula: No math—process-based

IP Subnet Calculator

Calculate Subnets for Your Network

This calculator helps you determine the number of subnets, hosts per subnet, and IP ranges when you subnet a network. It’s directly related to Section 3 of the IPv4 syllabus blog, where we discuss subnetting step-by-step.

CIDR Calculator

Determine Usable Hosts and IP Ranges

This calculator helps you calculate the number of usable hosts and IP ranges for a given CIDR notation (e.g., 192.168.0.0/23). It ties into Section 3 of the blog, where we discuss CIDR and supernetting.

Binary to Decimal Converter

Convert IP Addresses Between Formats

This converter helps you understand IP addresses in binary form, which is useful for learning how IPs work (Section 1 of the blog). For example, convert 192.168.1.1 to binary or vice versa.

Wildcard Mask Calculator

Generate Wildcard Masks for Configurations

This calculator generates wildcard masks for subnet masks, which are used in Cisco configurations (Section 4 and 5 of the blog). For example, a subnet mask of 255.255.255.0 has a wildcard mask of 0.0.0.255.