172.16.0.0/12
Private (RFC 1918) RFC 1918The 172.16.0.0/12 block spans 172.16.0.0 through 172.31.255.255, covering 1,048,576 IP addresses. AWS uses 172.31.0.0/16 as the default VPC CIDR in newly created accounts.
Network address — the base address of the block (172.16.0.0). All devices in this subnet share this prefix. Cannot be assigned to a host.
Broadcast address — packets sent to 172.31.255.255 are delivered to every device in the subnet. Also reserved — not assignable.
Usable hosts — the 1,048,574 addresses between those two that you can assign to servers, VMs, or interfaces.
Subnet mask — 255.240.0.0 is the dotted-decimal equivalent of /12. Older tools and Cisco configs use this format instead of CIDR slash notation.
Full Details
| CIDR Notation | 172.16.0.0/12 |
| Network Address | 172.16.0.0 |
| Broadcast Address | 172.31.255.255 |
| Subnet Mask | 255.240.0.0 |
| Wildcard Mask | 0.15.255.255 |
| Prefix Length | /12 |
| IP Address Class | Class B |
| Total IP Addresses | 1,048,576 |
| Usable Host Addresses | 1,048,574 |
| First Usable IP | 172.16.0.1 |
| Last Usable IP | 172.31.255.254 |
| Network (Hex) | 0xAC100000 |
| Broadcast (Hex) | 0xAC1FFFFF |
| Governing RFC | RFC 1918 |
| Address Type | Private (RFC 1918) |
Binary Representation
The first 12 bits (1s in the mask) identify the network. The remaining 20 bits identify hosts within the network.
Split into Equal Subnets
Split 172.16.0.0/12 into 2 equal /13 subnets (524,286 usable hosts each).
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 172.16.0.0/13 | 172.16.0.0 | 172.16.0.1 | 172.23.255.254 | 172.23.255.255 | 524,286 |
| 2 | 172.24.0.0/13 | 172.24.0.0 | 172.24.0.1 | 172.31.255.254 | 172.31.255.255 | 524,286 |
Split 172.16.0.0/12 into 4 equal /14 subnets (262,142 usable hosts each).
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 172.16.0.0/14 | 172.16.0.0 | 172.16.0.1 | 172.19.255.254 | 172.19.255.255 | 262,142 |
| 2 | 172.20.0.0/14 | 172.20.0.0 | 172.20.0.1 | 172.23.255.254 | 172.23.255.255 | 262,142 |
| 3 | 172.24.0.0/14 | 172.24.0.0 | 172.24.0.1 | 172.27.255.254 | 172.27.255.255 | 262,142 |
| 4 | 172.28.0.0/14 | 172.28.0.0 | 172.28.0.1 | 172.31.255.254 | 172.31.255.255 | 262,142 |
Split 172.16.0.0/12 into 8 equal /15 subnets (131,070 usable hosts each).
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 172.16.0.0/15 | 172.16.0.0 | 172.16.0.1 | 172.17.255.254 | 172.17.255.255 | 131,070 |
| 2 | 172.18.0.0/15 | 172.18.0.0 | 172.18.0.1 | 172.19.255.254 | 172.19.255.255 | 131,070 |
| 3 | 172.20.0.0/15 | 172.20.0.0 | 172.20.0.1 | 172.21.255.254 | 172.21.255.255 | 131,070 |
| 4 | 172.22.0.0/15 | 172.22.0.0 | 172.22.0.1 | 172.23.255.254 | 172.23.255.255 | 131,070 |
| 5 | 172.24.0.0/15 | 172.24.0.0 | 172.24.0.1 | 172.25.255.254 | 172.25.255.255 | 131,070 |
| 6 | 172.26.0.0/15 | 172.26.0.0 | 172.26.0.1 | 172.27.255.254 | 172.27.255.255 | 131,070 |
| 7 | 172.28.0.0/15 | 172.28.0.0 | 172.28.0.1 | 172.29.255.254 | 172.29.255.255 | 131,070 |
| 8 | 172.30.0.0/15 | 172.30.0.0 | 172.30.0.1 | 172.31.255.254 | 172.31.255.255 | 131,070 |
Split 172.16.0.0/12 into 16 equal /16 subnets (65,534 usable hosts each).
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 172.16.0.0/16 | 172.16.0.0 | 172.16.0.1 | 172.16.255.254 | 172.16.255.255 | 65,534 |
| 2 | 172.17.0.0/16 | 172.17.0.0 | 172.17.0.1 | 172.17.255.254 | 172.17.255.255 | 65,534 |
| 3 | 172.18.0.0/16 | 172.18.0.0 | 172.18.0.1 | 172.18.255.254 | 172.18.255.255 | 65,534 |
| 4 | 172.19.0.0/16 | 172.19.0.0 | 172.19.0.1 | 172.19.255.254 | 172.19.255.255 | 65,534 |
| 5 | 172.20.0.0/16 | 172.20.0.0 | 172.20.0.1 | 172.20.255.254 | 172.20.255.255 | 65,534 |
| 6 | 172.21.0.0/16 | 172.21.0.0 | 172.21.0.1 | 172.21.255.254 | 172.21.255.255 | 65,534 |
| 7 | 172.22.0.0/16 | 172.22.0.0 | 172.22.0.1 | 172.22.255.254 | 172.22.255.255 | 65,534 |
| 8 | 172.23.0.0/16 | 172.23.0.0 | 172.23.0.1 | 172.23.255.254 | 172.23.255.255 | 65,534 |
| 9 | 172.24.0.0/16 | 172.24.0.0 | 172.24.0.1 | 172.24.255.254 | 172.24.255.255 | 65,534 |
| 10 | 172.25.0.0/16 | 172.25.0.0 | 172.25.0.1 | 172.25.255.254 | 172.25.255.255 | 65,534 |
| 11 | 172.26.0.0/16 | 172.26.0.0 | 172.26.0.1 | 172.26.255.254 | 172.26.255.255 | 65,534 |
| 12 | 172.27.0.0/16 | 172.27.0.0 | 172.27.0.1 | 172.27.255.254 | 172.27.255.255 | 65,534 |
| 13 | 172.28.0.0/16 | 172.28.0.0 | 172.28.0.1 | 172.28.255.254 | 172.28.255.255 | 65,534 |
| 14 | 172.29.0.0/16 | 172.29.0.0 | 172.29.0.1 | 172.29.255.254 | 172.29.255.255 | 65,534 |
| 15 | 172.30.0.0/16 | 172.30.0.0 | 172.30.0.1 | 172.30.255.254 | 172.30.255.255 | 65,534 |
| 16 | 172.31.0.0/16 | 172.31.0.0 | 172.31.0.1 | 172.31.255.254 | 172.31.255.255 | 65,534 |
Common Use Cases
- → AWS default VPC (172.31.0.0/16)
- → Mid-size enterprise networks
- → Docker default bridge network (172.17.0.0/16)
- → Container orchestration clusters