Every device that communicates over the Internet relies on one foundational technology: the Internet Protocol (IP). Whether you are browsing the web, watching a video, or connecting to a remote server, IP ensures packets find the correct destination.
This guide summarizes the core concepts of IP addressing, subnetting, addressing types, DHCP allocation, NAT translation, and how hosts communicate across networks.
What Is an IP Address? #
An IP address is a logical identifier assigned to a device’s network interface. It ensures that:
- The device can communicate over a network
- Packets are delivered to the correct destination
- Responses reach the original sender
IPv4 Address Structure #
IPv4 addresses are 32-bit binary numbers, split into four 8-bit groups (octets).
Example:
192.168.1.5 → 11000000.10101000.00000001.00000101
Because raw binary is difficult to read, IPv4 uses dotted decimal notation, where each octet ranges from 0 to 255.
This gives IPv4 a total of over 4 billion possible addresses.
Network & Host Portions of an IP Address #
An IPv4 address is hierarchical:
- Network portion: Identifies the network
- Host portion: Identifies the device within that network
Example:
192.168.18.57 →
- Network:
192.168.18 - Host:
57
Routers only need to know how to reach networks, not individual hosts—making the Internet scalable.
This is similar to a telephone system: country code → area code → local number.
Subnet Masks: How Devices Know the Network Boundary #
An IP address alone does not tell a host which part is the network portion.
This is determined by the subnet mask, also 32 bits.
Common masks:
/8→255.0.0.0/16→255.255.0.0/24→255.255.255.0
A subnet mask identifies:
1bits → network portion0bits → host portion
Subnetting in Action #
Example: IP: 192.168.1.5 Mask: 255.255.255.0
yaml
Network = 192.168.1.0
Broadcast = 192.168.1.255
Calculating Hosts #
If a subnet has x host bits, usable hosts = 2^x - 2.
Example: /24 → 8 host bits → 2^8 - 2 = 254 usable hosts.
IP Address Classes #
IPv4 addresses have 5 classes:
| Class | Range of First Octet | Default Mask | Usage |
|---|---|---|---|
| A | 1–126 | /8 | Very large networks |
| B | 128–191 | /16 | Medium-sized networks |
| C | 192–223 | /24 | Small networks |
| D | 224–239 | n/a | Multicast |
| E | 240–255 | n/a | Experimental |
Example classifications:
15.4.234.12→ Class A150.110.12.50→ Class B200.14.193.67→ Class C
Public vs. Private IP Addresses #
Not all IPv4 addresses are routed on the Internet.
Private IP ranges (RFC 1918) are used internally:
- A Class: 10.0.0.0/8
- B Class: 172.16.0.0 – 172.31.255.255
- C Class: 192.168.0.0 – 192.168.255.255
Private addresses:
- Are not globally unique
- Are not routed on the Internet
- Provide additional security
- Enable internal network scalability
A special private range also exists: 127.0.0.0/8 → loopback testing (127.0.0.1).
Unicast, Broadcast, and Multicast #
Devices can communicate in three modes:
Unicast #
One-to-one communication.
Example: A PC requesting a webpage from a server.
Broadcast #
One-to-all communication within the LAN.
Example protocols using broadcast:
- ARP
- DHCP Discover
Example broadcast address for /24 network:
192.168.1.255
Multicast #
One-to-many, group-based communication.
Address range: 224.0.0.0 – 239.255.255.255
Used for:
- Live streaming
- Online gaming sessions
- Virtual classrooms
Corresponding multicast MAC addresses begin with:
01-00-5E
How IP Addresses Are Assigned #
IP addresses can be assigned:
Static Assignment #
A network admin manually enters:
- IP address
- Subnet mask
- Default gateway
Used for:
- Servers
- Printers
- Infrastructure devices
Advantages:
- Predictable addressing
- More control
Disadvantages:
- Time-consuming
- Prone to human error
Dynamic Assignment (DHCP) #
Most networks use DHCP for automatic address assignment.
DHCP provides:
- IP address
- Subnet mask
- Default gateway
- DNS server
DHCP Allocation Workflow #
- Discover → Client broadcasts a request (
255.255.255.255, MACFF:FF:FF:FF:FF:FF) - Offer → DHCP server proposes an address
- Request → Client asks to use the offered address
- ACK → Server confirms the assignment
Clients receive an address lease, which expires unless renewed.
Home routers often act as both DHCP server (LAN side) and DHCP client (WAN side).
NAT: Network Address Translation #
Since private IPs cannot be routed on the Internet, NAT converts them into public IPs.
Why NAT? #
- Conserves public IPv4 addresses
- Provides security by hiding internal addresses
Gateways & Address Boundaries #
A router connects multiple networks and defines network boundaries.
Each interface:
- Has its own IP address
- Represents a separate network
Hosts must know the router’s IP address → default gateway.
The gateway may be assigned:
- Statically
- Via DHCP
Home routers typically use:
- LAN side → private address (e.g.,
192.168.1.1) - WAN side → ISP-assigned public address
Conclusion #
The Internet Protocol is the backbone of network communication. Understanding IPv4 addressing, subnet masks, DHCP automation, and NAT translation is essential for troubleshooting, secure network design, and effective communication between devices.
As networks grow and IPv6 adoption accelerates, these fundamentals remain crucial for anyone involved in technology, cybersecurity, or software development.
