Reserved IP addresses in cloud subnets
Every cloud provider silently takes some addresses out of each subnet you create, so you always get fewer usable IPs than the subnet maths suggests. Here is exactly what each one reserves.
Reserved addresses by provider
| Provider | Reserved per subnet | Smallest subnet | Usable in a 10.0.0.0/24 |
|---|---|---|---|
| Standard | 2 | /32 | 254 / 256 |
| AWS | 5 | /28 | 251 / 256 |
| Azure | 5 | /29 | 251 / 256 |
| Google Cloud | 4 | /29 | 252 / 256 |
| Oracle Cloud | 3 | /30 | 253 / 256 |
Which addresses are reserved in a 10.0.0.0/24 block
Standard
In a 10.0.0.0/24 subnet, Standard makes these addresses unavailable:
| Address | Why it is unavailable |
|---|---|
| 10.0.0.0 | Network address |
| 10.0.0.255 | Broadcast address |
That leaves 254 of 256 addresses assignable. Smallest subnet allowed: /32. RFC 1812 § 4.2.3.1
AWS
In a 10.0.0.0/24 subnet, AWS makes these addresses unavailable:
| Address | Why it is unavailable |
|---|---|
| 10.0.0.0 | Network address |
| 10.0.0.1 | AWS VPC router |
| 10.0.0.2 | AWS VPC DNS |
| 10.0.0.3 | Reserved by AWS for future use |
| 10.0.0.255 | Broadcast address |
That leaves 251 of 256 addresses assignable. Smallest subnet allowed: /28. AWS — Subnet sizing for IPv4
Azure
In a 10.0.0.0/24 subnet, Azure makes these addresses unavailable:
| Address | Why it is unavailable |
|---|---|
| 10.0.0.0 | Network address |
| 10.0.0.1 | Azure default gateway |
| 10.0.0.2 | Azure DNS mapping |
| 10.0.0.3 | Azure DNS mapping |
| 10.0.0.255 | Broadcast address |
That leaves 251 of 256 addresses assignable. Smallest subnet allowed: /29. Azure — Virtual network FAQ
Google Cloud
In a 10.0.0.0/24 subnet, Google Cloud makes these addresses unavailable:
| Address | Why it is unavailable |
|---|---|
| 10.0.0.0 | Network address |
| 10.0.0.1 | Google Cloud default gateway |
| 10.0.0.254 | Reserved by Google Cloud for future use |
| 10.0.0.255 | Broadcast address |
That leaves 252 of 256 addresses assignable. Smallest subnet allowed: /29. Google Cloud — VPC subnets
Oracle Cloud
In a 10.0.0.0/24 subnet, Oracle Cloud makes these addresses unavailable:
| Address | Why it is unavailable |
|---|---|
| 10.0.0.0 | Network address |
| 10.0.0.1 | Oracle Cloud default gateway |
| 10.0.0.255 | Broadcast address |
That leaves 253 of 256 addresses assignable. Smallest subnet allowed: /30. Oracle Cloud — Networking overview
Official documentation
Each provider states these reservations in its own documentation:
| Provider | Official documentation |
|---|---|
| Standard | RFC 1812 § 4.2.3.1 (opens the provider’s documentation) |
| AWS | AWS — Subnet sizing for IPv4 (opens the provider’s documentation) |
| Azure | Azure — Virtual network FAQ (opens the provider’s documentation) |
| Google Cloud | Google Cloud — VPC subnets (opens the provider’s documentation) |
| Oracle Cloud | Oracle Cloud — Networking overview (opens the provider’s documentation) |
Frequently asked questions
- How many usable IP addresses are in a 10.0.0.0/24 subnet on Standard?
- A 10.0.0.0/24 subnet on Standard has 254 usable addresses out of 256, because Standard reserves 2 of them.
- How many usable IP addresses are in a 10.0.0.0/24 subnet on AWS?
- A 10.0.0.0/24 subnet on AWS has 251 usable addresses out of 256, because AWS reserves 5 of them.
- How many usable IP addresses are in a 10.0.0.0/24 subnet on Azure?
- A 10.0.0.0/24 subnet on Azure has 251 usable addresses out of 256, because Azure reserves 5 of them.
- How many usable IP addresses are in a 10.0.0.0/24 subnet on Google Cloud?
- A 10.0.0.0/24 subnet on Google Cloud has 252 usable addresses out of 256, because Google Cloud reserves 4 of them.
- How many usable IP addresses are in a 10.0.0.0/24 subnet on Oracle Cloud?
- A 10.0.0.0/24 subnet on Oracle Cloud has 253 usable addresses out of 256, because Oracle Cloud reserves 3 of them.