Subnet Calculator
Calculate subnet mask, network address, broadcast address, and usable host range from an IP address and CIDR prefix.
VLAN Capacity Calculator
Calculate VLAN capacity and plan broadcast domain sizing based on host count, traffic patterns, and performance targets.
bytes
%
VLANs Needed⧉
4.00
Plus 2 overhead = 6 total
Hosts per VLAN⧉
200.00
0.79% subnet utilization
Broadcast per VLAN⧉
1,000.00 pps
800.00 Kbps bandwidth
VLAN ID Usage⧉
0.00%
6 of 4094 VLAN IDs used
Future VLANs (Growth)⧉
6.00
920.00 hosts at 15% growth
Wasted IPs⧉
216.00
Unused addresses across all subnets
VLAN Utilization
Subnet Usage
0.79%
VLAN IDs Used
0.00%
Broadcast Domain Health
Broadcast Load
800.00 Kbps
Warning: High broadcast traffic. Consider smaller subnets.
Subnet Mask Comparison
| Mask | Max Hosts | VLANs | Utilization | Broadcast BW |
|---|---|---|---|---|
| /24 | 254.00 | 4 | 0.79% | 800.00 Kbps |
| /23 | 510.00 | 2 | 0.78% | 1,600.00 Kbps |
| /22 | 1,022.00 | 1 | 0.78% | 3,200.00 Kbps |
| /21 | 2,046.00 | 1 | 0.39% | 3,200.00 Kbps |
| /20 | 4,094.00 | 1 | 0.20% | 3,200.00 Kbps |
Planning notes, formulas, and examples
About the VLAN Capacity Calculator
VLANs segment a physical network into separate broadcast domains. Each VLAN limits the scope of broadcast traffic to its members, reducing noise and improving performance. However, oversized VLANs with too many hosts generate excessive broadcast traffic that degrades performance.
This calculator helps network engineers determine optimal VLAN sizes based on host count and acceptable broadcast traffic levels. The general recommendation is to keep broadcast domains under 250 hosts for standard office networks and under 500 for data centers.
Proper VLAN sizing balances segmentation benefits (performance, security, isolation) against management complexity (more VLANs = more ACLs, more routing). The goal is the smallest broadcast domain that's practical for your network architecture.
When This Page Helps
Oversized VLANs cause broadcast storms and performance issues. This calculator helps size VLANs appropriately based on host count and performance requirements.
How to Use the Inputs
- Enter the total number of hosts to be distributed across VLANs.
- Enter the target maximum hosts per VLAN.
- Enter the average broadcast packets per host per second.
- Review the number of VLANs needed and broadcast traffic per VLAN.
Formula used
VLANs Needed = ceil(total_hosts / max_per_vlan)
Broadcast Traffic = hosts_per_vlan × broadcasts_per_host
Broadcast Bandwidth = broadcast_packets × avg_packet_sizeExample Calculation
Result: 4 VLANs, 1,000 broadcast pps per VLAN
800 hosts / 200 per VLAN = 4 VLANs. Each VLAN: 200 hosts × 5 broadcast packets/sec = 1,000 broadcast pps. At 100 bytes per packet, that's about 800 Kbps of broadcast traffic per VLAN — well within acceptable limits.
Tips & Best Practices
- Keep broadcast domains under 250 hosts for user networks, 500 for data centers.
- Monitor broadcast traffic levels and split VLANs if broadcasts exceed 5% of bandwidth.
- Use private VLANs to add micro-segmentation within a VLAN.
- Align VLAN boundaries with security zones for defense in depth.
- VLANs 1 and 4095 are reserved — usable range is 2–4094.
- Document VLAN assignments in a network management system.
VLAN Design Principles
Effective VLAN design follows the principle of minimal broadcast domains. Each VLAN should contain only hosts that need direct Layer 2 communication. Hosts that primarily communicate via IP (Layer 3) should be in separate VLANs with routed interconnection.
Broadcast Traffic Impact
Every host on a VLAN sees every broadcast frame. ARP, DHCP, NetBIOS, and other protocols generate broadcasts. With 200 hosts generating 5 broadcasts per second each, that's 1,000 broadcast frames per second — each processed by every host on the VLAN.
Modern VLAN Alternatives
For cloud and container environments, traditional VLANs are being supplemented by software-defined networking (SDN), security groups, and microsegmentation. These provide finer-grained control without the scaling limitations of 802.1Q VLANs.
Sources & Methodology
Last updated:
Frequently Asked Questions
The 802.1Q standard supports VLAN IDs 1–4094 (VLAN 0 and 4095 are reserved). This gives a theoretical maximum of 4,094 VLANs. Practical limits depend on switch hardware — most enterprise switches support 1,000–4,000 VLANs.
A broadcast storm occurs when broadcast traffic overwhelms the network, consuming all available bandwidth. It typically results from switching loops, misconfigured devices, or an oversized broadcast domain with too many chatty hosts.
Generally yes. A 1:1 mapping between VLANs and IP subnets is the most common and manageable design. Traffic between VLANs must be routed (Layer 3), enabling firewall and ACL control at VLAN boundaries.
For office networks: 50–250 hosts. For data centers: 100–500 hosts. For IoT or high-broadcast environments: 50–100 hosts. The key metric is broadcast traffic: if broadcasts exceed 3–5% of VLAN bandwidth, the VLAN is too large.
VXLAN (Virtual Extensible LAN) extends VLAN segmentation to Layer 3, supporting up to 16 million segments. Use VXLAN in data centers and multi-site networks where 4,094 VLANs are insufficient or where overlapping VLANs are needed.
VLANs isolate broadcast domains, preventing hosts in different VLANs from communicating at Layer 2. Traffic between VLANs must pass through a router where ACLs and firewalls can filter it. This provides network-level segmentation.
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