A /27 subnet is the maximum allocation per dedicated server or VPS, providing 30 usable IP addresses. This is widely used because it balances efficient IP utilization with practical hosting needs, while staying within common allocation policies enforced by providers and registries.
What a /27 Means
A /27 refers to the subnet mask:
- CIDR notation: /27
- Subnet mask: 255.255.255.224
- Total IP addresses: 32
- Usable IP addresses: 30
Why only 30 usable?
Out of the 32 total IPs:
- 1 IP is reserved for the network address
- 1 IP is reserved for the broadcast address
That leaves 30 usable IPs for servers, services, or assignments.
Example of a /27 IP Range
Example subnet: 192.168.1.0/27
- Network address: 192.168.1.0
- Usable range: 192.168.1.1 – 192.168.1.30
- Broadcast address: 192.168.1.31
Full Breakdown of Common IPv4 Subnet Sizes
| CIDR | Subnet Mask | Total IPs | Usable IPs | Typical Use Case |
|---|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 | Single host |
| /31 | 255.255.255.254 | 2 | 2* | Point-to-point links |
| /30 | 255.255.255.252 | 4 | 2 | Small network segments |
| /29 | 255.255.255.248 | 8 | 6 | Small VPS allocations |
| /28 | 255.255.255.240 | 16 | 14 | Medium VPS |
| /27 | 255.255.255.224 | 32 | 30 | Max typical per server/VPS |
| /26 | 255.255.255.192 | 64 | 62 | Larger deployments |
| /25 | 255.255.255.128 | 128 | 126 | Subnet splitting |
| /24 | 255.255.255.0 | 256 | 254 | Standard network block |
| /23 | 255.255.254.0 | 512 | 510 | Larger allocations |
| /22 | 255.255.252.0 | 1024 | 1022 | ISP-level |
| /21 | 255.255.248.0 | 2048 | 2046 | Regional blocks |
| /20 | 255.255.240.0 | 4096 | 4094 | Enterprise networks |
| /19 | 255.255.224.0 | 8192 | 8190 | Large enterprise |
| /18 | 255.255.192.0 | 16384 | 16382 | ISP allocation |
| /17 | 255.255.128.0 | 32768 | 32766 | ISP allocation |
| /16 | 255.255.0.0 | 65536 | 65534 | Large network |
| /8 | 255.0.0.0 | 16M+ | ~16M | Internet-scale |
Key Terms Explained
CIDR (Classless Inter-Domain Routing)
- The “/27” format
- Indicates how many bits are used for the network portion
- Higher number = smaller subnet
Subnet Mask
- Defines network vs host portion
- Example: 255.255.255.224 = /27
Network Address
- First IP in the block
- Identifies the subnet itself
- Not usable
Broadcast Address
- Last IP in the block
- Used to communicate with all devices in the subnet
- Not usable
Usable IP Addresses
- IPs available for assignment to servers, VPS instances, or services
Public vs Private IPs
- Public IPs are routable on the internet
- Private IPs (e.g., 192.168.x.x) are internal only
Why /27 is the Practical Limit per Server or VPS
- Efficient allocation without excessive IP waste
- Common policy limit from data centers and IP providers
- Easier justification for ARIN/RIPE/APNIC requirements
- Larger blocks like /26 or /24 usually require:
- Multi-server deployments
- Load balancing setups
- Detailed IP justification
Summary
- /27 = 32 total IPs, 30 usable
- It is the standard maximum allocation per single server or VPS
- Larger allocations exist but require stronger justification and broader infrastructure use
