255.255.128.0 Subnet Mask
255.255.128.0 is the subnet mask for a /17 network — 32,766 usable hosts out of 32,768 addresses.
CIDR Prefix
/17
Wildcard Mask
0.0.127.255
Total Addresses
32,768
Usable Hosts
32,766
Network Bits
17
Host Bits
15
255.255.128.0 in Binary
Each octet is eight bits. The highlighted bits are the 17 network bits; the rest are the 15 host bits that vary within the subnet.
255
255
128
0
Networks Using 255.255.128.0
| Network | Host Range | Broadcast |
|---|---|---|
| 10.0.0.0/17 | 10.0.0.1 – 10.0.127.254 | 10.0.127.255 |
| 172.16.0.0/17 | 172.16.0.1 – 172.16.127.254 | 172.16.127.255 |
| 192.168.0.0/17 | 192.168.0.1 – 192.168.127.254 | 192.168.127.255 |
Neighbouring Masks
Frequently Asked Questions
What CIDR prefix is 255.255.128.0?
255.255.128.0 is /17 in CIDR notation. The mask sets the first 17 of the 32 bits in an IPv4 address to 1, marking them as the network portion, and leaves the remaining 15 bits as 0 for hosts.
How many hosts does 255.255.128.0 allow?
A network with mask 255.255.128.0 holds 32,768 addresses, of which 32,766 are usable by hosts — the network address and the broadcast address are reserved.
What is the wildcard mask for 255.255.128.0?
The wildcard mask for 255.255.128.0 is 0.0.127.255. It is the bitwise inverse: every 1 in the subnet mask becomes a 0 and every 0 becomes a 1. Cisco access lists and OSPF network statements take the wildcard form rather than the subnet mask.
Standards
- RFC 950 — Internet Standard Subnetting Procedure
Defines the dotted-decimal subnet mask itself, and the rule that the network and broadcast addresses are not assignable to hosts.
- RFC 4632 — Classless Inter-Domain Routing (CIDR)
Establishes the /17 prefix notation that 255.255.128.0 is equivalent to, and requires masks to be contiguous — which is why exactly 33 of the 4.3 billion possible values are valid.