CIDR /25Private (RFC 1918)
/25 Subnet Mask (255.255.255.128) - Usable Hosts & CIDR | ipcalc.net
Everything about /25 subnets: Subnet mask 255.255.255.128, wildcard mask 0.0.0.127, 126 usable hosts, binary breakdown, and Cisco configuration templates.
Enter any notation: 192.168.1.1/24, 10.0.0.1 255.255.255.0, or plain IP
Subnet Mask Prefix: /25Netmask: 255.255.255.128
Presets:
32-Bit Subnet Boundary Visualizer
Click any bit position to adjust the CIDR prefix boundary
Network (25 bits)
Host (7 bits)
Octet 1192Mask: 255
11111111
Octet 2168Mask: 255
11111111
Octet 31Mask: 255
11111111
Octet 40Mask: 128
10000000
Usable Hosts
126
Total IPs: 128
Network Address
192.168.1.0
Prefix: /25
Usable Host Range
192.168.1.1
192.168.1.126
Broadcast Address
192.168.1.127
Subnet Broadcast
Detailed Subnet Breakdown
Private (RFC 1918)Subnet Mask
255.255.255.128
Wildcard Mask (Cisco ACL)
0.0.0.127
Hexadecimal IP / Mask
0xC0A80100 / 0xFFFFFF80
Integer / Decimal IP
3232235776
IP Class & Routing
Class C • Classless Inter-Domain Routing (CIDR)
Reverse DNS (in-addr.arpa)
0.1.168.192.in-addr.arpa
Cisco IOS Command Templates
ip address 192.168.1.0 255.255.255.128
access-list 1 permit 192.168.1.0 0.0.0.127
Technical Subnet Specifications
Prefix Length/25
Dotted Decimal Subnet Mask255.255.255.128
Wildcard Mask (Inverse)0.0.0.127
Total Available IP Addresses128
Usable Host Capacity126 hosts
Network Bits vs Host Bits25 Network / 7 Host
Binary Subnet Mask11111111.11111111.11111111.10000000
Cisco IOS Configuration
Copy-paste templates for Cisco router and switch interface setup:
! Configure Interface
interface GigabitEthernet0/0/1
ip address 192.168.1.1 255.255.255.128
no shutdown
! Access-Control List
access-list 10 permit 192.168.1.0 0.0.0.127
Tip: Wildcard mask is computed by inverting the subnet mask (
~mask).Typical Network Use Cases for /25
A /25 network block provides 128 total IP addresses with 126 usable host interfaces.
Designated Role: Half Class C (126 usable).
Frequently Asked Questions: /25 (255.255.255.128)
Authoritative answers to common /25 subnetting, host capacity, and networking questions.
Q1How many usable hosts are in a /25 subnet?
A /25 subnet provides 126 usable host IP addresses out of 128 total addresses. In IPv4 networking, 2 addresses are reserved: the network address (192.168.1.0) and the directed broadcast address (192.168.1.127). Formula: 2^(32 - 25) - 2 = 126 usable hosts.
Q2What is the subnet mask and wildcard mask for /25?
The dotted-decimal subnet mask for a /25 prefix is 255.255.255.128. The corresponding wildcard mask (used in Cisco ACLs and OSPF network statements) is 0.0.0.127. In binary, the subnet mask consists of 25 network bits (1s) followed by 7 host bits (0s).
Q3What are the network, broadcast, and usable IP ranges for 192.168.1.0/25?
For the 192.168.1.0/25 subnet: the Network Address is 192.168.1.0, the Broadcast Address is 192.168.1.127, and the usable host range extends from 192.168.1.1 through 192.168.1.126. Any host interface configured in this subnet must have an IP within this range and netmask 255.255.255.128.
Q4What is a /25 subnet typically used for in network design?
A /25 subnet is typically deployed for half class c (126 usable). In enterprise and cloud environments (such as AWS VPCs or Azure VNets), /25 allocations provide the optimal balance between host capacity and address conservation.
Q5What does /25 mean in CIDR notation?
Classless Inter-Domain Routing (CIDR) notation expresses the subnet mask as a forward slash followed by the prefix length. A /25 prefix indicates that the first 25 bits of the 32-bit IPv4 address are locked for network identification, leaving the remaining 7 bits available for addressing host interfaces.