/17 Subnet Mask (255.255.128.0)
| Prefix | /17 |
|---|---|
| Subnet mask | 255.255.128.0 |
| Wildcard mask | 0.0.127.255 |
| Binary mask | 11111111.11111111.10000000.00000000 |
| Total addresses | 32,768 |
| Usable hosts | 32,766 |
| Host bits | 15 |
| Subnets of /17 in a /16 | 2 |
e.g. 10.0.0.5/22 or 10.0.0.5 255.255.252.0
| Network address | 172.16.0.0 | |
|---|---|---|
| Broadcast address | 172.16.127.255 | |
| First usable host | 172.16.0.1 | |
| Last usable host | 172.16.127.254 | |
| Total addresses | 32,768 | |
| Usable hosts | 32,766 | |
| Subnet mask | 255.255.128.0 | |
| Wildcard mask | 0.0.127.255 | |
| CIDR notation | 172.16.0.0/17 | |
| IP class | Class B (legacy) | |
| Address type | Private (RFC 1918) | |
| IP address (binary) | 10101100.00010000.00000000.00000000 | |
| Subnet mask (binary) | 11111111.11111111.10000000.00000000 |
■ network bits ■ host bits
| Requested hosts | CIDR | First host | Last host | Broadcast | Usable hosts |
|---|
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What is a /17 subnet?
A /17 subnet uses the first 17 bits of an IPv4 address for the network and leaves 15 bits for hosts. Its subnet mask is 255.255.128.0, and it contains 2¹⁵ = 32,768 addresses, of which 32,766 can be assigned to devices. Typical use: Half of a /16 (32,766 usable hosts); used to split a VPC or campus range into two halves. Use the subnet calculator above to check any /17 network.
/17 subnet example
For 172.16.0.0/17: network address 172.16.0.0, usable hosts 172.16.0.1 – 172.16.127.254, broadcast address 172.16.127.255, wildcard mask 0.0.127.255.
/17 networks in 172.16.0.0/16
A /16 holds 2 /17 networks:
- 172.16.0.0/17
- 172.16.128.0/17
Frequently asked questions
How many usable IPs are in a /17?
32,766. The block has 32,768 addresses; the first is the network address and the last is the broadcast address.
What is the subnet mask for /17?
255.255.128.0, or 11111111.11111111.10000000.00000000 in binary.
How many /17 subnets are in a /16?
2 (2¹), because a /17 uses 1 more network bits than a /16.
What is the difference between /17 and /16?
A /16 (255.255.0.0) is twice as large: 65,536 addresses and 65,534 usable hosts, spanning two consecutive /17 blocks such as 172.16.0.0–172.16.255.255.