How is a subnet mask calculated?
CIDR (Classless Inter-Domain Routing) notation expresses how many bits of an IP block are reserved for the network portion via a /prefix. For example, /24 means 24 of 32 bits are the network, leaving 8 bits (256 addresses) for hosts — 2 of which (network and broadcast) are unusable, leaving 254 usable host addresses. This calculator runs all arithmetic in your browser; nothing is sent to a server.
Subnetting is critical for VPC/VLAN segmentation, firewall rule planning and IP pool allocation in server infrastructure. /31 and /32 are special cases: per RFC 3021, /31 uses both addresses as hosts on point-to-point links (no broadcast is reserved), while /32 represents a single host address.
When should you use Subnet / CIDR Calculator?
The KEYDAL Subnet / CIDR Calculator tool is a browser-based utility that developers, system administrators, SEO specialists and enterprise technology teams use in their daily operations. It requires no installation, is free, and produces results instantly. It is designed so local teams can run audits without connecting to server environments and run analyses without touching production.
Typical scenarios include: post-migration verification, comparing domain or hosting providers, diagnosing customer issues, security auditing (pre-pentest reconnaissance), root-cause analysis of email deliverability problems, validating CDN or proxy configuration, surfacing technical audit data for SEO teams, and rapid information gathering during incident response. You can copy results as text and share them or paste them into internal documentation.
The KEYDAL infrastructure team provides web hosting, VPS, dedicated server management, server hardening, DNS configuration and SSL/TLS deployment services from Türkiye. Beyond these tools, we deliver server setup and operations support across Hetzner, OVHcloud, Contabo, DigitalOcean and Turkish providers.
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