/15 Subnet Mask ReferenceIPv4
Pair two adjacent /16s and the natural summary is a /15: mask <code>255.254.0.0</code>, 131,072 addresses. It is the tidy answer when two campuses or two data halls share one routing domain.
/15 facts at a glance
- Subnet mask
- 255.254.0.0
- Wildcard mask
- 0.1.255.255
- Binary mask
- 11111111.11111110.00000000.00000000
- Total addresses
- 131,072
- Usable hosts
- 131,070 (excludes network & broadcast)
- Block size
- 131,072 addresses (217)
- Typical role
- Large enterprise and carrier aggregation
Example /15 networks
Three consecutive /15 blocks, starting at the /15 boundary that contains 198.51.100.0:
| Network | Usable range | Usable hosts |
|---|---|---|
| 198.50.0.0/15 | 198.50.0.1 – 198.51.255.254 | 131,070 |
| 198.52.0.0/15 | 198.52.0.1 – 198.53.255.254 | 131,070 |
| 198.54.0.0/15 | 198.54.0.1 – 198.55.255.254 | 131,070 |
How to calculate a /15 mask
A /15 mask sets the first 15 bits of a 32-bit number to 1 and leaves the remaining 17 bits as 0. In binary that reads 11111111.11111110.00000000.00000000, which converts to dotted decimal 255.254.0.0. Each block covers a contiguous run of 217 = 131,072 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 0.1.255.255.
Where /15 is used
- Merging two /16 sites under a single advertisement.
- Paired data-center blocks planned symmetrically from day one.
- Supernetting practice on the odd/even second-octet boundary.
Famous resident: <code>198.18.0.0/15</code> is reserved for benchmarking network equipment (RFC 2544), spanning 198.18.0.0 through 198.19.255.255.
The second octet must be even: <code>130.10.0.0/15</code> is legal and covers 130.10.0.0 through 130.11.255.255, while <code>130.11.0.0/15</code> is misaligned.
Frequently asked questions
What mask does a /15 use?
<code>255.254.0.0</code>, wildcard <code>0.1.255.255</code>.
How many addresses are in a /15?
131,072 total; 131,070 usable after removing the network and broadcast placeholders.
How many /16s are in a /15?
Exactly two: an even-numbered /16 plus the odd one immediately following it.
Open this block in a calculator
Open the /15 block in the subnet calculator