VLSM & Subnet Planner
Plan multiple IPv4 subnets from one parent network. Enter the required host count for each department, VLAN, CCTV group or site segment and Zee Links will allocate appropriately sized subnets from largest requirement to smallest.
Subnet Requirements
VLSM Allocation
| Requirement | Hosts Requested | Network | CIDR | Subnet Mask | Usable Hosts | First Host | Last Host | Broadcast |
|---|
How VLSM Works
VLSM — Variable Length Subnet Masking lets you divide one address block into subnets of different sizes. Instead of giving every department the same number of addresses, each group receives a subnet sized for its actual requirement.
Example: If CCTV needs 60 hosts, office PCs need 30, Wi-Fi needs 20 and management needs 10, using VLSM avoids wasting a full /24 for every group.
Planning method
- Choose the parent network.
- List required hosts for each segment.
- Sort requirements from largest to smallest.
- Allocate the smallest suitable subnet for each requirement.
- Verify that every allocated subnet stays inside the parent network and does not overlap.
Important practical points
- Traditional IPv4 LAN subnets reserve the network and broadcast addresses, so usable hosts are normally total addresses minus two.
- A /31 can be used for suitable point-to-point links under RFC 3021 and does not provide the usual network/broadcast host model.
- A /32 represents a single IPv4 address and is commonly used for host routes rather than a normal LAN subnet.
- VLSM is an addressing technique; it does not itself create VLANs, routing or DHCP scopes.
CCTV / Network Example
| Segment | Hosts | Possible subnet |
|---|---|---|
| CCTV Cameras | 60 | /26 · 62 usable hosts |
| Office PCs | 30 | /27 · 30 usable hosts |
| Wi-Fi | 20 | /27 · 30 usable hosts |
| Management | 10 | /28 · 14 usable hosts |
This kind of planning is useful when designing CCTV VLANs, office networks, wireless networks and management networks inside a larger address block.