When to Use VLSM vs Equal-Size Subnets

You're designing a network and need to divide your address space. Do you carve it into equal chunks, or use Variable Length Subnet Masking (VLSM) to optimize allocation? The answer depends on your priorities.

Equal-Size Subnets: The Simple Approach

With equal subnetting, you divide your network into identically-sized blocks. A /24 becomes four /26 networks, each with 62 usable hosts.

Advantages:

• Easy to plan and document
• Simple to summarize and route
• Consistent addressing scheme across sites
• Easier for junior staff to understand

Disadvantages:

• Wastes addresses when segment sizes vary
• May run out of subnets before running out of addresses

VLSM: The Efficient Approach

VLSM lets you use different prefix lengths for different segments. A point-to-point link gets a /30 (2 hosts), while the data center gets a /23 (510 hosts).

Subnet Calculator Plan your VLSM allocation with accurate host counts

Advantages:

• Minimal address waste
• Right-sized subnets for each purpose
• More subnets from the same address space

Disadvantages:

• More complex to plan
• Harder to summarize routes
• Documentation becomes critical
• Easier to make allocation mistakes

A Practical Example

Given 192.168.1.0/24, you need subnets for:

• Server VLAN: 50 hosts
• User VLAN: 100 hosts
• Guest VLAN: 25 hosts
• Management VLAN: 10 hosts
• Two point-to-point links: 2 hosts each

Equal-Size Approach

The largest need is 100 hosts, requiring a /25 (126 hosts). Equal /25 subnets give you only two subnets from a /24—not enough.

You'd need to use /26 (62 hosts max), but that doesn't fit the 100-host requirement. Equal sizing fails here without a larger starting block.

VLSM Approach

Segment	Hosts Needed	Subnet	Size
Users	100	192.168.1.0/25	126
Servers	50	192.168.1.128/26	62
Guests	25	192.168.1.192/27	30
Management	10	192.168.1.224/28	14
Link 1	2	192.168.1.240/30	2
Link 2	2	192.168.1.244/30	2

Everything fits in a single /24, with 192.168.1.248-255 left for growth.

When to Choose Each

Use equal-size subnets when:

• Address space is plentiful
• Simplicity is more valuable than efficiency
• You're deploying many similar sites
• Route summarization is a priority

Use VLSM when:

• Address space is constrained
• Segment sizes vary significantly
• You need maximum subnets from limited space
• You have experienced staff to manage it

The Hybrid Approach

Many organizations use a mix. Equal-size /24s for each site (simple summarization), then VLSM within each /24 to allocate VLANs efficiently. This balances simplicity at the WAN level with efficiency at the LAN level.