/15 · 255.254.0.0
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Two /16s. Sometimes used to give a single VPC room for two /16-sized environments (production and staging) under one aggregate.
Key numbers
| Prefix length | /15 (15 network bits, 17 host bits) |
| Subnet mask | 255.254.0.0 |
| Mask in binary | 11111111.11111110.00000000.00000000 |
| Wildcard mask | 0.1.255.255 |
| Total addresses | 131,072 |
| Usable hosts | 131,070 (total minus network and broadcast) |
| Contains | 512 × /24 networks |
| Block size | Increments of 2 in octet 2 |
Example ranges
Private (RFC 1918) blocks of this size. Click one to open it in the calculator.
| Block | First address | Last address | Usable hosts |
|---|---|---|---|
| 10.0.0.0/15 | 10.0.0.0 | 10.1.255.255 | 10.0.0.1 – 10.1.255.254 |
| 172.16.0.0/15 | 172.16.0.0 | 172.17.255.255 | 172.16.0.1 – 172.17.255.254 |
Usable addresses in the cloud
Cloud providers reserve a few addresses in every subnet for the router, DNS and future use, so the usable count is lower than the formula gives.
| Provider | Usable in a /15 | Notes |
|---|---|---|
| AWS VPC subnet | n/a | Not allowed: AWS subnets must be between /16 and /28. |
| Azure virtual network subnet | 131,067 | Allowed. Azure reserves the first four addresses and the last one. |
| Google Cloud subnet | 131,068 | Allowed. Google Cloud reserves the first two and the last two addresses. |
How the numbers are derived
An IPv4 address has 32 bits. A /15 uses 15 of them for the network, leaving 17 host bits, so the block has 217 = 131,072 addresses. The first address (all host bits 0) is the network address and the last (all host bits 1) is the broadcast address, which leaves 131,070 for hosts. The subnet mask is 15 ones followed by 17 zeros, written in dotted decimal as 255.254.0.0; the wildcard mask 0.1.255.255 is its inverse, used in Cisco ACLs and OSPF configuration.
FAQ
How many hosts can a /15 have?
131,072 addresses in total, of which 131,070 are usable after removing the network and broadcast addresses. Cloud providers reserve a few more: 131,067 usable in AWS and Azure, 131,068 in Google Cloud.
How many /24 subnets fit in a /15?
512. Each step of the prefix length halves or doubles the block, so a /15 contains 2^(24 − 15) = 512 networks of /24 size.