Net Practice Pro

Complete IP Addressing & Subnetting Guide

Essential Tool

🎯 The Magic Decoder Chart

The single most important chart in networking - MEMORIZE THIS!

2⁷

128

2⁶

2⁵

2⁴

2³

2²

2¹

2⁰

💡 The Pattern: Each position is double the previous → 1, 2, 4, 8, 16, 32, 64, 128

💡 Why It Matters: This chart converts binary to decimal AND solves subnet problems!

How to Use: Binary → Decimal

Binary to Decimal Converter

Enter Binary (8 bits):

Example 1: Convert 11000000 to decimal

Position	128	64	32	16	8	4	2	1
Binary	1	1	0	0	0	0	0	0
Add	128	64	-	-	-	-	-	-

128 + 64 = 192

Answer: 11000000 = 192

Example 2: Convert 10101100 to decimal

Position	128	64	32	16	8	4	2	1
Binary	1	0	1	0	1	1	0	0
Add	128	-	32	-	8	4	-	-

128 + 32 + 8 + 4 = 172

Answer: 10101100 = 172

Core Skill

🔄 Decimal to Binary Conversion

Master both directions: Decimal → Binary and Binary → Decimal

Decimal to Binary Converter

Enter Decimal (0-255):

Method: Decimal → Binary

1 Write the Magic Numbers

128, 64, 32, 16, 8, 4, 2, 1

2 Start from 128 - does it fit?

If YES → write "1" and subtract. If NO → write "0" and move on.

3 Repeat for each position until you reach 0

Example: Convert 207 to Binary

Start with: 207

#	Power	Value	Fits?	Bit	Remainder
1	2⁷ = 128	207	✔ Yes	1	79
2	2⁶ = 64	79	✔ Yes	1	15
3	2⁵ = 32	15	✘ No	0	15
4	2⁴ = 16	15	✘ No	0	15
5	2³ = 8	15	✔ Yes	1	7
6	2² = 4	7	✔ Yes	1	3
7	2¹ = 2	3	✔ Yes	1	1
8	2⁰ = 1	1	✔ Yes	1	0

11001111

Decimal 207 = Binary 11001111

Common Subnet Mask Values

These appear constantly in networking - memorize them!

Decimal	Binary	Common Use
255	11111111	Network portion (all 1s)
254	11111110	/31 mask
252	11111100	/30 mask (4 IPs, 2 usable)
248	11111000	/29 mask (8 IPs)
240	11110000	/28 mask (16 IPs)
224	11100000	/27 mask (32 IPs)
192	11000000	/26 mask (64 IPs)
128	10000000	/25 mask (128 IPs)
0	00000000	Host portion (all 0s)

🎯 Pro Tips

Binary	Decimal	Note
11111111	255	All bits on — memorize!
10000000	128	Only the highest bit
11000000	192	128 + 64

💡 Remember: More 1s from the left = bigger number. Practice daily — you'll get fast!

Network Types

📋 IP Address Classes

Legacy system still used for understanding network size

Class	Range	Default Mask	CIDR	Networks	Hosts/Network	Use
A	1-126	255.0.0.0	/8	126	16,777,214	Huge orgs
B	128-191	255.255.0.0	/16	16,384	65,534	Med orgs
C	192-223	255.255.255.0	/24	2,097,152	254	Small nets
D	224-239	Multicast
E	240-255	Experimental/Reserved

Why skip 127? The entire 127.0.0.0/8 range is reserved for loopback. 127.0.0.1 = localhost (your computer talking to itself)

Private IP Ranges (RFC 1918)

These are NOT routable on the public internet - use for internal networks

Class	Private Range	CIDR	Total IPs	Common Use
A	10.0.0.0 - 10.255.255.255	10.0.0.0/8	16,777,216	Large enterprises
B	172.16.0.0 - 172.31.255.255	172.16.0.0/12	1,048,576	Medium orgs
C	192.168.0.0 - 192.168.255.255	192.168.0.0/16	65,536	Home/small office

Special Purpose Addresses

Address/Range	Purpose	Example
127.0.0.0/8	Loopback	127.0.0.1 (localhost)
169.254.0.0/16	APIPA (auto-config when DHCP fails)	169.254.1.1
0.0.0.0/8	This network / Default route	0.0.0.0
255.255.255.255	Limited broadcast	Broadcasts to local network

Critical Concept

📐 Subnet Intervals Explained

The "block size" or "magic number" for finding subnet boundaries

Interval Calculator

Subnet Mask Octet:

What is the Interval?

The interval (or block size) is how many IP addresses are in each subnet. It's the key to finding network boundaries quickly!

How to Calculate the Interval

1 Look at the subnet mask

Example: 255.255.255.192

2 Find the "interesting octet" (the one that's not 255 or 0)

In this case: 192 (4th octet)

3 Subtract from 256

256 - 192 = 64

The interval is 64!

Interval Table — Memorize This!

CIDR	Subnet Mask	Last Octet	Interval (256-X)	Total IPs	Usable
/24	255.255.255.0	0	256	256	254
/25	255.255.255.128	128	128	128	126
/26	255.255.255.192	192	64	64	62
/27	255.255.255.224	224	32	32	30
/28	255.255.255.240	240	16	16	14
/29	255.255.255.248	248	8	8	6
/30	255.255.255.252	252	4	4	2

Example: Find all subnets in 192.168.1.0/26

1 Find the interval

Mask = 255.255.255.192
Interval = 256 - 192 = 64

2 Count by the interval in the interesting octet

Start at 0, count by 64: 0, 64, 128, 192

Subnet	Network	First Usable	Last Usable	Broadcast
1	192.168.1.0	192.168.1.1	192.168.1.62	192.168.1.63
2	192.168.1.64	192.168.1.65	192.168.1.126	192.168.1.127
3	192.168.1.128	192.168.1.129	192.168.1.190	192.168.1.191
4	192.168.1.192	192.168.1.193	192.168.1.254	192.168.1.255

Visual Tool

📊 Subnet Block Divider

Watch a network block get divided into subnets in real time

Interactive Visualizer

Base Network:

Starting CIDR:

Slide to subnet into: /24 (no split)

Practical Skills

🧮 Calculate Everything from a Mask

Given an IP and mask, find network, broadcast, and host range

Interactive Subnet Calculator

IP Address:

CIDR:

The Process (Step-by-Step)

Example: 172.16.45.200/20 - Find all parameters

1 Convert /20 to subnet mask

/20 means 20 bits are "on" (1s)
First 2 octets: 255.255 (16 bits)
Third octet needs 4 more bits: 11110000 = 240
Mask: 255.255.240.0

2 Find the interval (block size)

Interesting octet: 240 (3rd octet)
256 - 240 = 16

3 Find which subnet 45 falls into

Count by 16 in 3rd octet: 0, 16, 32, 48
45 is between 32 and 48, so it's in the subnet starting at 32

4 Calculate all addresses

Network Address:	172.16.32.0
First Usable:	172.16.32.1
Last Usable:	172.16.47.254
Broadcast:	172.16.47.255
Total Hosts:	4,096
Usable Hosts:	4,094

🎯 Quick Formulas

What	Formula
Network	Start of interval
Broadcast	(Start of next interval) − 1
First Usable	Network + 1
Last Usable	Broadcast − 1
Total Hosts	2^{(32 − CIDR)}
Usable Hosts	Total − 2

Master Skill

🔪 How to Subnet a Network

Break one big network into smaller subnets

Interactive Subnet Creator

Base Network:

Base CIDR:

Subnets Needed:

The Subnetting Formula

2^n ≥ Number of Subnets Needed

Where n = number of bits to borrow from the host portion

Example: Split 192.168.1.0/24 into 4 subnets

1 How many bits do we need?

2^1 = 2 (not enough)
2^2 = 4 (perfect!)
We need to borrow 2 bits

2 New CIDR notation

Original: /24
Add 2 borrowed bits: /24 + 2 = /26

3 New subnet mask

/26 = 255.255.255.192
Interval: 256 - 192 = 64

4 List all subnets

Subnet	Network	Usable Range	Broadcast	Hosts
1	192.168.1.0	192.168.1.1 - 192.168.1.62	192.168.1.63	62
2	192.168.1.64	192.168.1.65 - 192.168.1.126	192.168.1.127	62
3	192.168.1.128	192.168.1.129 - 192.168.1.190	192.168.1.191	62
4	192.168.1.192	192.168.1.193 - 192.168.1.254	192.168.1.255	62

Common Subnetting Scenarios

Need X Subnets	Borrow Bits	Get Subnets	From /24 becomes
2 subnets	1 bit	2	/25 (128 hosts each)
3-4 subnets	2 bits	4	/26 (62 hosts each)
5-8 subnets	3 bits	8	/27 (30 hosts each)
9-16 subnets	4 bits	16	/28 (14 hosts each)
17-32 subnets	5 bits	32	/29 (6 hosts each)
33-64 subnets	6 bits	64	/30 (2 hosts each)

🎯 The Magic Decoder Chart

2⁷

128

2⁶

2⁵

2⁴

2³

2²

2¹

2⁰

🛠️ Smart Unified Network Assistant

IP Address

Subnet Mask

CIDR (e.g. /24)

Subnets Needed

Decimal to Binary (e.g. 207, 172)

💡 Fill in one or more fields above, then press Analyze & Solve

Cheat Sheet

📝 Quick Reference Guide

CIDR to Everything Chart

CIDR	Mask	Wildcard	Total IPs	Usable	Class C Equiv
/8	255.0.0.0	0.255.255.255	16,777,216	16,777,214	256 C
/16	255.255.0.0	0.0.255.255	65,536	65,534	256 C
/17	255.255.128.0	0.0.127.255	32,768	32,766	128 C
/18	255.255.192.0	0.0.63.255	16,384	16,382	64 C
/19	255.255.224.0	0.0.31.255	8,192	8,190	32 C
/20	255.255.240.0	0.0.15.255	4,096	4,094	16 C
/21	255.255.248.0	0.0.7.255	2,048	2,046	8 C
/22	255.255.252.0	0.0.3.255	1,024	1,022	4 C
/23	255.255.254.0	0.0.1.255	512	510	2 C
/24	255.255.255.0	0.0.0.255	256	254	1 C
/25	255.255.255.128	0.0.0.127	128	126	1/2 C
/26	255.255.255.192	0.0.0.63	64	62	1/4 C
/27	255.255.255.224	0.0.0.31	32	30	1/8 C
/28	255.255.255.240	0.0.0.15	16	14	1/16 C
/29	255.255.255.248	0.0.0.7	8	6	1/32 C
/30	255.255.255.252	0.0.0.3	4	2	Point-to-point
/31	255.255.255.254	0.0.0.1	2	2	P2P (no broadcast)
/32	255.255.255.255	0.0.0.0	1	1	Host route

Powers of 2 (Essential!)

Memorize these for instant subnet calculations

2^n	Value	2^n	Value	2^n	Value
2^0	1	2^8	256	2^16	65,536
2^1	2	2^9	512	2^17	131,072
2^2	4	2^10	1,024	2^18	262,144
2^3	8	2^11	2,048	2^19	524,288
2^4	16	2^12	4,096	2^20	1,048,576
2^5	32	2^13	8,192	2^24	16,777,216
2^6	64	2^14	16,384	2^32	4,294,967,296
2^7	128	2^15	32,768

Host / Mask Quick Picks

Use this table when an exam or design question says "I need X hosts" and you must choose the right subnet mask.

Needed Hosts (min)	Smallest CIDR	Mask (last octet)	Total IPs	Usable Hosts
2	/30	255.255.255.252	4	2
4–6	/29	255.255.255.248	8	6
10–14	/28	255.255.255.240	16	14
20–30	/27	255.255.255.224	32	30
40–62	/26	255.255.255.192	64	62
80–126	/25	255.255.255.128	128	126
130–254	/24	255.255.255.0	256	254

🎓 How to use this

Step 1: Take the number of hosts you need.
Step 2: Find the first row where "Usable Hosts" is ≥ your number.
Step 3: That row gives you the CIDR and subnet mask to choose.
Memory trick: /30 → 2, /29 → 6, /28 → 14, /27 → 30, /26 → 62 (roughly double each time).

🌐 TCP/IP Model Overview

The four-layer model that powers the modern Internet

Layer #	TCP/IP Layer	OSI Equivalent	Primary Function	Key Protocols	Data Unit
4	Application	Application + Presentation + Session	User-facing services and data formatting	HTTP, HTTPS, FTP, SSH, DNS, DHCP, SMTP, POP3, IMAP, SNMP, Telnet	Data / Message
3	Transport	Transport	End-to-end delivery, reliability, flow control	TCP, UDP	Segment (TCP) / Datagram (UDP)
2	Internet	Network	Logical addressing and routing across networks	IP (v4/v6), ICMP, ARP, IGMP	Packet
1	Network Access	Data Link + Physical	Physical transmission and local delivery	Ethernet, Wi-Fi (802.11), PPP, Frame Relay	Frame / Bits

📦 Encapsulation flow: Data → Segment → Packet → Frame → Bits. Each layer wraps the data from the layer above with its own header (and sometimes trailer), then passes it down.

🔀 TCP vs UDP Comparison

When to use each transport protocol

Feature	TCP (Transmission Control Protocol)	UDP (User Datagram Protocol)
Connection	Connection-oriented (3-way handshake)	Connectionless
Reliability	Guaranteed delivery (ACKs, retransmission)	Best-effort, no guarantee
Ordering	In-order delivery (sequence numbers)	No ordering
Flow Control	Yes (sliding window)	No
Error Checking	Checksum + retransmission	Checksum only (optional in IPv4)
Header Size	20–60 bytes	8 bytes
Speed	Slower (overhead from reliability)	Faster (minimal overhead)
Use Cases	Web (HTTP/S), Email, FTP, SSH	DNS queries, VoIP, video streaming, gaming, DHCP

🤝 TCP 3-Way Handshake:

1 SYN — Client sends a synchronize request to the server.
2 SYN-ACK — Server acknowledges and sends its own SYN back.
3 ACK — Client acknowledges. Connection is now established.

🚪 Common Port Numbers

Essential ports every network engineer should know

Port	Protocol	Service	Description
20	TCP	FTP Data	File transfer (data channel)
21	TCP	FTP Control	File transfer (command channel)
22	TCP	SSH	Secure remote login & file transfer (SCP/SFTP)
23	TCP	Telnet	Unencrypted remote login (legacy)
25	TCP	SMTP	Sending email between servers
53	TCP/UDP	DNS	Domain name resolution
67/68	UDP	DHCP	Dynamic IP address assignment (server/client)
69	UDP	TFTP	Trivial file transfer (no authentication)
80	TCP	HTTP	Web traffic (unencrypted)
110	TCP	POP3	Retrieving email (downloads to client)
143	TCP	IMAP	Retrieving email (server-synced)
161/162	UDP	SNMP	Network device monitoring & management
443	TCP	HTTPS	Secure web traffic (TLS/SSL)
3389	TCP	RDP	Remote Desktop Protocol (Windows)

Port ranges: Well-Known (0–1023) are reserved for standard services. Registered (1024–49151) are assigned to applications. Dynamic/Ephemeral (49152–65535) are used by clients for temporary connections.

🔧 Essential Network Protocols

Key protocols and what they do at each layer

Internet Layer Protocols

Protocol	Full Name	Purpose
IP	Internet Protocol	Logical addressing and routing of packets across networks. IPv4 uses 32-bit addresses; IPv6 uses 128-bit.
ICMP	Internet Control Message Protocol	Error reporting and diagnostics (ping, traceroute). Sends messages like "Destination Unreachable" and "Time Exceeded."
ARP	Address Resolution Protocol	Maps a known IP address to a MAC address on the local network. Works via broadcast requests.
IGMP	Internet Group Management Protocol	Manages multicast group memberships on local network segments.

Application Layer Protocols

Protocol	Full Name	Purpose
DNS	Domain Name System	Translates domain names (e.g., google.com) into IP addresses. Uses hierarchical name servers (Root → TLD → Authoritative).
DHCP	Dynamic Host Configuration Protocol	Automatically assigns IP addresses, subnet masks, default gateways, and DNS servers to clients. Uses DORA: Discover → Offer → Request → Acknowledge.
NAT	Network Address Translation	Translates private IP addresses to public IPs (and back) at a router. Enables multiple devices to share one public IP. Types: Static NAT, Dynamic NAT, PAT (Port Address Translation).
HTTP/S	HyperText Transfer Protocol (Secure)	Foundation of web communication. GET, POST, PUT, DELETE methods. HTTPS adds TLS encryption on port 443.
FTP	File Transfer Protocol	Transfers files between client and server. Uses two channels: control (port 21) and data (port 20). SFTP (over SSH) is the secure alternative.
SSH	Secure Shell	Encrypted remote access to devices. Replaced Telnet. Also used for tunneling and secure file transfer (SCP, SFTP).

📨 IPv4 Packet Header Structure

What's inside every IP packet

Field	Size	Purpose
Version	4 bits	IP version (4 for IPv4)
IHL	4 bits	Header length in 32-bit words (min 5 = 20 bytes)
DSCP / ECN	8 bits	Quality of Service (traffic prioritization)
Total Length	16 bits	Entire packet size in bytes (max 65,535)
Identification	16 bits	Fragment identification for reassembly
Flags + Offset	16 bits	Fragmentation control (DF, MF) and fragment offset
TTL	8 bits	Time To Live — decremented at each hop, packet discarded at 0
Protocol	8 bits	Upper-layer protocol (6 = TCP, 17 = UDP, 1 = ICMP)
Header Checksum	16 bits	Error detection for the header only
Source Address	32 bits	Sender's IP address
Destination Address	32 bits	Receiver's IP address
Options	Variable	Optional fields (rarely used; e.g., record route, timestamp)

Minimum IPv4 Header = 20 bytes (5 × 32-bit words) | Maximum = 60 bytes (15 × 32-bit words with options)

🔒 Network Security Essentials

Core security concepts for network certification

Concept	Description
Firewall	Filters traffic based on rules (source/destination IP, port, protocol). Types: stateless (packet filtering), stateful (tracks connections), application-layer (deep inspection).
ACL	Access Control List — ordered set of permit/deny rules applied at router interfaces. Standard ACLs filter by source IP; Extended ACLs filter by source, destination, port, and protocol.
VPN	Virtual Private Network — creates an encrypted tunnel over a public network. Common types: IPsec (site-to-site), SSL/TLS VPN (remote access), WireGuard.
TLS/SSL	Transport Layer Security — encrypts data in transit. Used by HTTPS, SMTPS, IMAPS. Replaced the older SSL protocol. Uses certificates for authentication.
DMZ	Demilitarized Zone — a perimeter network segment that exposes public-facing services (web, email) while shielding the internal LAN.
IDS / IPS	Intrusion Detection / Prevention System — monitors network traffic for threats. IDS alerts; IPS actively blocks. Can be signature-based or anomaly-based.

📡 Network Device Reference

What each device does and where it operates

Device	OSI Layer	Addresses Used	Function
Hub	Layer 1 (Physical)	None	Broadcasts all traffic to every port. No intelligence. Legacy device.
Switch	Layer 2 (Data Link)	MAC addresses	Forwards frames only to the correct port using a MAC address table. Creates separate collision domains.
Router	Layer 3 (Network)	IP addresses	Routes packets between different networks/subnets. Creates separate broadcast domains. Uses routing tables.
L3 Switch	Layer 2 + 3	MAC + IP	Switch with routing capability. Can perform inter-VLAN routing at hardware speed.
Firewall	Layer 3–7	IP + Ports	Inspects and filters traffic based on security rules. Can be hardware or software.
Access Point	Layer 1–2	MAC addresses	Bridges wireless clients to a wired network. Manages Wi-Fi connections (802.11).
Load Balancer	Layer 4–7	IP + Ports	Distributes traffic across multiple servers for availability and performance.

⚡ Networking Quick Formulas

Handy formulas for certification exams and daily work

Usable Hosts = 2^{(32 − CIDR)} − 2

Number of Subnets = 2^{bits borrowed}

Magic Number (Block Size) = 256 − subnet mask octet value

Broadcast Address = Network Address + Block Size − 1 (in the relevant octet)

Wildcard Mask = 255.255.255.255 − Subnet Mask

Throughput = Window Size ÷ RTT (basic TCP throughput estimate)

🎓 Exam Tips

Topic	Tip
Subnetting shortcut	Find the "interesting" (non-255, non-0) octet in the mask. The block size in that octet determines all subnet boundaries.
AND operation	IP AND Mask = Network Address. Only AND the "interesting" octet; 255 octets stay the same, 0 octets become 0.
TTL values	Default TTL: 64 (Linux), 128 (Windows), 255 (Cisco). Useful for OS fingerprinting.
Private ranges	10.0.0.0/8 · 172.16.0.0/12 · 192.168.0.0/16 — never routed on the public Internet.
CIDR /31	RFC 3021 — point-to-point links, no broadcast address needed.

Advanced

📐 VLSM Calculator

Variable Length Subnet Masking — allocate different-sized subnets from one network to minimize waste

Base Network IP

CIDR Prefix

Subnet Requirements

Add the subnets you need — VLSM will sort by size and allocate optimally.

📖 What is VLSM?

Variable Length Subnet Masking (VLSM) allows you to use different subnet masks within the same network, unlike traditional subnetting which uses a single mask for all subnets.

Why use VLSM? It minimizes IP address waste. A department with 200 hosts gets a /24, while a point-to-point link with 2 hosts gets a /30 — all from the same parent network.

Key rule: Always allocate the largest subnet first, then fit smaller ones into the remaining space.

Hosts Needed	Host Bits	CIDR	Block Size	Usable Hosts
1–2	2	/30	4	2
3–6	3	/29	8	6
7–14	4	/28	16	14
15–30	5	/27	32	30
31–62	6	/26	64	62
63–126	7	/25	128	126
127–254	8	/24	256	254

Utilities

🔧 Network Tools

Practical utilities for network planning and troubleshooting

🔍 Subnet Overlap Checker

Check if two or more subnets overlap in address space

Subnet 1 IP

CIDR

Subnet 2 IP

CIDR

📦 Route Summarization (Supernetting)

Find the smallest CIDR block that covers multiple contiguous subnets

Network 1 IP

CIDR

Network 2 IP

CIDR

🎯 IP-in-Subnet Checker

Check if a specific IP address belongs to a given subnet

IP Address

Subnet Network

CIDR

Exam Simulator

🏆 Network Certification Drill

Timed practice questions to sharpen your subnetting skills under pressure

⏱ Timer

0 Streak

0 Correct

0 Attempted

Press "Start Challenge" to begin!

📈 Session History

Visualizer

📊 Network Diagram Generator

Visualize subnets as an interactive hub-and-spoke topology diagram

Base Network IP

CIDR Prefix

Number of Subnets