🌐 VLSM Subnet Calculator
Variable Length Subnet Masking — Plan multiple subnets from a single IP block with real CIDR math
Enter each subnet name and the number of hosts required. The calculator will assign the smallest possible CIDR block for each.
| CIDR Prefix | Subnet Mask | Total Addresses | Usable Hosts | Wildcard Mask | Typical Use |
|---|---|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | 0.255.255.255 | Large ISP / RFC 1918 Class A |
| /16 | 255.255.0.0 | 65,536 | 65,534 | 0.0.255.255 | Enterprise / RFC 1918 Class B |
| /20 | 255.255.240.0 | 4,096 | 4,094 | 0.0.15.255 | Large campus segment |
| /22 | 255.255.252.0 | 1,024 | 1,022 | 0.0.3.255 | Medium campus / ISP allocation |
| /24 | 255.255.255.0 | 256 | 254 | 0.0.0.255 | Standard LAN / VLAN |
| /25 | 255.255.255.128 | 128 | 126 | 0.0.0.127 | Half subnet split |
| /26 | 255.255.255.192 | 64 | 62 | 0.0.0.63 | Small office segment |
| /27 | 255.255.255.224 | 32 | 30 | 0.0.0.31 | Small workgroup |
| /28 | 255.255.255.240 | 16 | 14 | 0.0.0.15 | Server cluster / mgmt |
| /29 | 255.255.255.248 | 8 | 6 | 0.0.0.7 | Small server group |
| /30 | 255.255.255.252 | 4 | 2 | 0.0.0.3 | Point-to-point WAN link |
| /31 | 255.255.255.254 | 2 | 2* | 0.0.0.1 | P2P (RFC 3021, no broadcast) |
| /32 | 255.255.255.255 | 1 | 1 | 0.0.0.0 | Host route / loopback |
| Use Case | Recommended CIDR | Usable Hosts | Notes |
|---|---|---|---|
| Point-to-Point Link | /30 | 2 | Router-to-router WAN |
| Management VLAN | /28 — /29 | 6 — 14 | Network devices only |
| Server Farm (small) | /27 — /28 | 14 — 30 | Physical servers, VMs |
| Home Lab VLAN | /27 — /26 | 30 — 62 | With room for VMs |
| Small Office LAN | /26 — /25 | 62 — 126 | 10–50 users typical |
| Medium Office LAN | /24 | 254 | Standard VLAN size |
| Large LAN / Wifi | /23 | 510 | High-density wireless |
| Campus Segment | /22 — /20 | 1,022 — 4,094 | Multiple buildings |
| IoT Segment | /25 — /24 | 126 — 254 | Isolated VLAN |
| Voice / VoIP | /25 — /26 | 62 — 126 | Dedicated QoS VLAN |
| Scenario | Base Block | Subnets Needed | Smallest Subnet | Addresses Used |
|---|---|---|---|---|
| Home Lab 3-VLAN | 192.168.1.0/24 | 3 | /27 | ~96 of 256 |
| Small Office | 192.168.0.0/24 | 4 | /28 | ~208 of 256 |
| Campus Multi-VLAN | 10.0.0.0/16 | 8 | /27 | ~2,144 of 65,536 |
| ISP /22 Allocation | 203.0.113.0/22 | 4 | /25 | ~640 of 1,024 |
| Data Center Segs | 10.10.0.0/20 | 6 | /28 | ~528 of 4,096 |
VLSM-calculator helps to share nets in smaller subnets of various sizes. It is a useful resource for those that work with IP-addresses because it allows to create subnets that match exactly to your needs, without waste of address space.
Such calculators are simple to use, even so still strong. They make it possible to find IP-addresses, count the amount of hosts, control network masks and research available ranges. Some of them even allow to plan a whole net using only one page.
Make Different Size Subnets with a VLSM Calculator
That simplifies the process, when one handles several levels of subntes.
VLSM beats the average subnetting. In traditional subnetting all subnets must have the same size. VLSM changes that, allowing to split nets into subnets of different sizes.
So, if one part of a net requires 1000 hosts and another only 20, one can set the sizes right. Today we do not want too waste IPv4-addresses.
A good VLSM-calculator will show for every subnet the subnet address, the mask, the first available IP, the last available IP and the broadcast address. Some of them also care about automatic placement of subnets and best placement of hosts without overlaps. It really is useful, when one designs a net from scratch.
There are tools that handle both IPv4 and IPv6 protocols. They provide info about network address, subnet mask, IP-range and others. Some extras include conversions between decimal and binary together with VLSM and CIDR-calculations.
Support for CIDR usually covers from /8 until /32, because it deals with IPv4.
Subnetting of nets has many benefits. It logically separates the net, improves security by means of limiting traffic between subnets and reduces broadcast traffic. One can fit the amount of IP-addresses for every subnet according to particular needs.
Such resources well serve students of networking, network engineers and IT-professionals. Some calculators are made user-friendly for pupils, even so stay professionally fit for actual work. Even a visual subnet-calculator can show how one can further split a subnet, with the biggest subnets in the center and thesmallest around.
Key things to know are, that VLSM simply allows subnets to have different sizes. For masks bigger than /24, one counts the last octet from 256 to find the number of valid addresses for that mask. Getting comfort with those basics does make use of any VLSM-calculator much more simple.
