Calculating and Implementing Subnets
Overview
Subnetting is the process of dividing a network into smaller network segments. Understanding subnetting is crucial for network administration and configuration in Linux systems.
Subnetting Basics
IP Address Structure
An IPv4 address consists of 4 octets (32 bits total):
192.168.1.10
Each octet can range from 0 to 255.
Subnet Mask
A subnet mask determines which part of an IP address is the network and which part is the host.
255.255.255.0- /24 network (254 usable hosts)255.255.0.0- /16 network (65,534 usable hosts)255.255.255.128- /25 network (126 usable hosts)
CIDR Notation
CIDR (Classless Inter-Domain Routing) uses a slash followed by the number of network bits:
Examples:
192.168.1.0/24 = 255.255.255.010.0.0.0/8 = 255.0.0.0172.16.0.0/12 = 255.240.0.0Linux Networking Commands
ip addr show
Display network interfaces and their IP addresses.
ip route show
Display routing table.
ifconfig
Older command to view/configure network interfaces (may need net-tools package).
Key Calculations
- Network Address: First address in the subnet (all host bits = 0)
- Broadcast Address: Last address in the subnet (all host bits = 1)
- Usable Hosts: Total hosts - 2 (network & broadcast)
- Formula: Usable hosts = 2^(32 - prefix) - 2
Subnet Calculator
Enter an IP address and CIDR prefix to calculate subnet information.
| Network Address | 192.168.1.0 |
|---|---|
| Subnet Mask | 255.255.255.0 |
| Broadcast Address | 192.168.1.255 |
| First Usable IP | 192.168.1.1 |
| Last Usable IP | 192.168.1.254 |
| Total Hosts | 256 |
| Usable Hosts | 254 |