Try: , ,
| Subnet | Hosts needed | Network | Mask | Usable range | Spare |
|---|---|---|---|---|---|
| #1 | 60 | 192.168.10.0/26 | 255.255.255.192 | 192.168.10.1 – 192.168.10.62 | 2 |
| #2 | 28 | 192.168.10.64/27 | 255.255.255.224 | 192.168.10.65 – 192.168.10.94 | 2 |
| #3 | 12 | 192.168.10.96/28 | 255.255.255.240 | 192.168.10.97 – 192.168.10.110 | 2 |
| #4 | 2 | 192.168.10.112/30 | 255.255.255.252 | 192.168.10.113 – 192.168.10.114 | 0 |
116 of 256 addresses allocated (45%). Subnets are placed largest first so each one stays aligned.
How to use it
- Enter the network you want to divide, such as 192.168.10.0/24.
- List how many hosts each subnet needs, separated by commas or spaces: 60, 28, 12, 2.
- Read the allocation: each requirement gets the smallest subnet that fits, placed largest first so nothing overlaps.
What the result means
VLSM (variable-length subnet masking) gives each subnet its own prefix instead of cutting the network into equal pieces. That wastes far fewer addresses.
For every requirement the table shows the subnet it got, its mask, the usable range and how many addresses are spare. A subnet for n hosts needs n + 2 addresses (network and broadcast), rounded up to a power of two: 60 hosts need 64 (/26), 28 need 32 (/27), 12 need 16 (/28), 2 need 4 (/30).
Placing the largest subnets first keeps every block aligned on its own boundary. If a requirement doesn't fit in what's left, it's marked so you can choose a bigger starting network.
Frequently asked questions
What is VLSM?
Variable-length subnet masking: dividing a network into subnets of different sizes. A /24 can hold one /26 for 60 hosts, one /27 for 28 hosts and several /30 links, instead of eight equal /27s.
Why allocate the largest subnet first?
A subnet must start on a multiple of its own size. Placing big blocks first means each following smaller block always lands on a valid boundary, with no gaps or overlaps.
How many addresses does a subnet for 2 hosts need?
Four, a /30: network, two hosts and broadcast. It's the classic size for a link between two routers. Some networks use /31 (RFC 3021) for these links instead, which needs only two.
What is the difference between FLSM and VLSM?
FLSM (fixed-length) uses one mask for every subnet, so each is as big as the largest one needs. VLSM sizes each subnet to its own requirement, which saves addresses.
Is VLSM on the CCNA exam?
Yes. Designing a VLSM scheme from host requirements is a standard CCNA task. Practise with this calculator, then check yourself with the subnetting practice questions.