/15 Subnet: Mask 255.254.0.0

A /15 is two /16s side by side. The second octet must be even, and the block covers that even number plus the odd one after it.

/15 at a glance

Subnet mask
255.254.0.0
Wildcard mask
0.1.255.255
Usable hosts
131,070
Total addresses
131,072 (217)
Block size (second octet)
2
Network / host bits
15 / 17
Mask in hex
0xFFFE0000

Mask in binary: 11111111.11111110.00000000.00000000

Network bits Host bits

Try it: which /15 is an address in?

Network address
198.18.0.0/15
First usable host
198.18.0.1
Last usable host
198.19.255.254
Broadcast address
198.19.255.255
Next /15 starts at
198.20.0.0
Open this in the full subnet calculator (binary view, exports, cloud reserved IPs) →

How many /15 networks fit

How /15 relates to /8, /16 and /24 blocks
Parent block Relationship
/8 128 × /15 fit inside one /8
/16 One /15 covers 2 × /16
/24 One /15 covers 512 × /24

A /15 is exactly two /16s or 512 /24s.

Worked example: 198.19.44.1/15

A lab appliance uses 198.19.44.1. Is that inside the benchmarking range 198.18.0.0/15?

  1. The mask is 255.254.0.0. The second octet (254) is the "interesting" one — the first that is not 255.
  2. Block size = 256 − 254 = 2. Networks start at multiples of 2 in the second octet: 0, 2, 4, …
  3. The second octet of 198.19.44.1 is 19. 19 ÷ 2 = 9 remainder 1, so the block starts at 9 × 2 = 18.
  4. Network = 198.18.0.0 (octets after the second become 0). Broadcast = 18 + 2 − 1 = 19, giving 198.19.255.255 (octets after it become 255).
  5. Usable hosts: 198.18.0.1 to 198.19.255.254, which is 217 − 2 = 131,070 addresses.

Same thing in binary (network bits | host bits):

Address  11000110.0001001|1.00101100.00000001
Mask     11111111.1111111|0.00000000.00000000
Network  11000110.0001001|0.00000000.00000000

Where /15 is used in real networks

  • Benchmarking range 198.18.0.0/15

    RFC 2544 reserves 198.18.0.0 to 198.19.255.255 for network device benchmarking. Test tools like traffic generators use it so lab traffic never collides with real addresses.

  • Pairing two /16s

    If a site was given 10.40.0.0/16 and later needs more room, choosing 10.41.0.0/16 as the second block lets both be summarised as 10.40.0.0/15. Choosing 10.42.0.0/16 would not.

Common /15 mistakes

  • Writing 10.41.0.0/15. The second octet of a /15 must be even, so it snaps back to 10.40.0.0/15.
  • Using 198.18.0.0/15 for a production LAN because it "looks private". It is reserved for benchmarking and some security tools flag it.

/15 FAQ

How many hosts are in a /15?

131,070 usable: 2^17 = 131,072 addresses minus network and broadcast.

What is the range of 198.18.0.0/15?

198.18.0.0 to 198.19.255.255. A /15 covers two values of the second octet, here 18 and 19.

What is the wildcard mask for /15?

0.1.255.255. The mask's second octet is 254, and 255 − 254 = 1.

Related tools

Subnet Calculator Full /15 breakdown with binary and exports Wildcard Mask Calculator ACL and OSPF wildcard for /15 and every other prefix CIDR Calculator Split 198.18.0.0/15 into smaller blocks VLSM Calculator Mix /15 with other sizes in one plan Subnet Mask Calculator Convert mask ↔ prefix ↔ host count Subnetting Practice Drill questions like this one, with visual answers