/25 vs /27 — Subnet Comparison
A /25 subnet is 4× larger than a /27. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /25 has 22 = 4 times as many addresses.
126 usable hosts — half a /24
Typical Uses
- →Public vs private half of a /24
- →Department sub-segment
- →Smaller cloud application subnets
30 usable hosts — small workgroup
Typical Uses
- →Small workgroup LAN
- →Network device management subnet
- →Cloud NAT gateway subnet
Key Differences
How 4 /27 Subnets Divide a /25
Example using 10.0.0.0/25 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/27 | 10.0.0.0 | 10.0.0.1 | 10.0.0.30 | 10.0.0.31 | 30 |
| 2 | 10.0.0.32/27 | 10.0.0.32 | 10.0.0.33 | 10.0.0.62 | 10.0.0.63 | 30 |
| 3 | 10.0.0.64/27 | 10.0.0.64 | 10.0.0.65 | 10.0.0.94 | 10.0.0.95 | 30 |
| 4 | 10.0.0.96/27 | 10.0.0.96 | 10.0.0.97 | 10.0.0.126 | 10.0.0.127 | 30 |
FAQ
What is the difference between /25 and /27?
A /25 has 126 usable hosts
and a /27 has 30.
The subnet masks differ: /25 uses 255.255.255.128
while /27 uses 255.255.255.224.
Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means
/25 is exactly 4× larger.
How many /27 subnets fit in a /25?
Exactly 4 /27 subnets fit perfectly inside one /25 with no wasted space. To split a /25 into /27s, just increment the last 2 bits of the network address for each new subnet.
Which should I choose?
/25 is typically used for: Half a /24 — public/private split. /27 is better for: Small workgroup / management subnet. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.