An IP subnet cheat sheet can be helpful for quickly understanding and calculating subnets. Here’s a cheat sheet covering some essential information:
Subnetting Basics
- Subnet Mask Format:
- Written in dotted-decimal format (e.g., 255.255.255.0).
- CIDR Notation:
- CIDR (Classless Inter-Domain Routing) represents the subnet mask using a slash followed by the subnet prefix length (e.g., /24).
Subnetting Formula
- Number of Subnets (2^n):
- n = Number of subnet bits.
- Number of Hosts (2^(32-n) – 2):
- n = Number of host bits.
Subnetting Rules
- All-Zero Subnet:
- Represents the network itself (e.g., 192.168.1.0).
- All-One Subnet:
- Reserved for broadcast (e.g., 192.168.1.255).
- Subnet Size:
- Determines the number of usable host addresses.
Subnet Mask Table
| Subnet Mask | CIDR Notation | Usable IPs | Subnet Size |
|---|---|---|---|
| 255.255.255.252 | /30 | 2 | Point-to-Point Link |
| 255.255.255.248 | /29 | 6 | Small Office |
| 255.255.255.240 | /28 | 14 | Small Office |
| 255.255.255.224 | /27 | 30 | Small Office |
| 255.255.255.192 | /26 | 62 | Medium Office |
| 255.255.255.128 | /25 | 126 | Medium Office |
| 255.255.255.0 | /24 | 254 | Large Office |
| 255.255.254.0 | /23 | 510 | Large Office |
| 255.255.252.0 | /22 | 1022 | Large Office |
| 255.255.248.0 | /21 | 2046 | Large Office |
| 255.255.240.0 | /20 | 4094 | Large Office |
Subnetting Examples
- Example 1:
- IP Range: 192.168.1.0 – 192.168.1.255
- Subnet Mask: 255.255.255.0 (CIDR: /24)
- Example 2:
- IP Range: 10.0.0.0 – 10.0.15.255
- Subnet Mask: 255.255.240.0 (CIDR: /20)
VLSM (Variable Length Subnet Masking)
- Allocate Larger Subnets to Areas with More Hosts:
- Efficiently use IP addresses based on specific network requirements.
Subnetting Tools
- Online Subnet Calculators:
- Various tools available for calculating subnets and CIDR notation.
Subnetting Practice
- Practice Calculations:
- Practice subnetting exercises to reinforce understanding.
Subnetting Best Practices
- Plan Ahead:
- Plan for future growth when designing subnets.
- Documentation:
- Keep detailed documentation of subnet allocations.
This cheat sheet provides a quick reference for IP subnetting concepts, rules, and examples. Subnetting is a crucial skill for network administrators and engineers, enabling efficient use of IP address space and optimizing network performance.