Network subnetting divides larger IP networks into smaller, manageable segments. This partitioning improves network security, optimizes performance, and enables efficient IP address allocation. Think of subnetting like dividing a large office building into departments – each gets its own space while remaining part of the whole structure.
Why should I subnet my network?
Isolate systems and control traffic flow between network segments
Reduce broadcast traffic and network congestion
Group devices logically by function, department, or location
Allocate IP addresses efficiently based on actual needs
Simplify troubleshooting and implement access controls
CIDR stands for Classless Inter-Domain Routing.
| CIDR | Subnet Mask | Usable IPs | Typical Usage |
|---|---|---|---|
/32 |
255.255.255.255 | 1 | Single host (loopback, point-to-point) |
/30 |
255.255.255.252 | 2 | Point-to-point links (router interconnects) |
/24 |
255.255.255.0 | 254 | Typical LAN / small office |
/16 |
255.255.0.0 | 65,534 | Large organization network |
/8 |
255.0.0.0 | 16,777,214 | ISP ranges / very large networks |
Consider these factors when choosing your subnet size:
1. Current number of devices you need to support
2. Expected growth over the next 2-3 years (multiply current needs by 1.5-2x)
3. Network segmentation requirements (security zones, departments, etc.)
4. Reserved addresses for network infrastructure (routers, switches, etc.)
For example, if you currently have 100 devices and expect 50% growth, choose a /24 subnet (254 usable addresses) rather than a /25 (126 addresses).
While both masks help define network boundaries, they serve different purposes:
Subnet masks use 1s for network bits and 0s for host bits (e.g., 255.255.255.0) Wildcard masks are the inverse, using 0s for network bits and 1s for host bits (e.g., 0.0.0.255)
Wildcard masks are primarily used in access control lists (ACLs) and routing configurations to specify which bits should be matched exactly and which can vary.
Follow these best practices to prevent IP conflicts:
Yes, but only if they’re contiguous and properly aligned.
For example: Two /25 networks (192.168.1.0/25 and 192.168.1.128/25) can be combined into one /24
1. The networks must share the same parent network
2. All IP addresses must be renumbered during consolidation
3. Plan your initial subnetting carefully to minimize the need for future consolidation.
Always reserve these addresses in your planning:
1. Network address (first address in the range)
2. Broadcast address (last address in the range)
3. Gateway address (typically first or last usable address)
4. Key infrastructure (DHCP servers, DNS servers)
5. Management addresses for network equipment
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