How many usable IP addresses are in a /17 subnet?

A /17 subnet contains 32,768 total IP addresses. In standard networking, 2 addresses are reserved (the Network ID and Broadcast address), leaving 32,766 usable host IP addresses.

What is the wildcard mask for /17?

The wildcard mask for /17 (255.255.128.0) is 0.0.127.255. Wildcard masks are commonly used in Cisco IOS Access Control Lists (ACLs) and OSPF routing configurations.

Home/Subnet Calculator//17 CIDR

/16 /18

IPv4 CIDR Reference

/17 Subnet Mask — 255.255.128.0 Netmask & Host Calculator

A /17 subnet prefix allocates 255.255.128.0 as its subnet mask. It provides 32,768 total IPv4 addresses and 32,766 usable host addresses with a wildcard mask of 0.0.127.255.

Subnet Mask

255.255.128.0

Usable Hosts

32,766

Total Addresses

32,768

Wildcard Mask

0.0.127.255

Interactive /17 Subnet Calculator

Binary Architecture of a /17 Mask

An IPv4 address consists of 32 bits. In a /17 prefix, the first 17 bits are locked as binary 1s (representing the network prefix), while the remaining 15 bits are binary 0s (reserved for host assignment).

Prefix Length: /17

Binary Mask: 11111111.11111111.10000000.00000000

Dotted Decimal: 255.255.128.0

Formula: 2^(32 - 17) = 32,768 IPs

When Should You Use a /17 Subnet?

General purpose local subnet or cloud partition.

Optimized for low-waste routing and efficient IP allocation.

Frequently Asked Questions about /17 Subnets

The subnet mask for a /17 CIDR prefix is 255.255.128.0. In binary notation, this is 11111111.11111111.10000000.00000000 (17 contiguous network bits and 15 host bits).