IP Range Calculator
IP Address Classification & Subnetting Reference
CIDR (Classless Inter-Domain Routing) uses IP/prefix-length to denote networks. The prefix length is the number of consecutive 1-bits in the subnet mask. E.g., /24 = 255.255.255.0 (first 24 bits = network, last 8 = host).
Subnet masks identify the network portion (1=network, 0=host). Wildcard masks are the bitwise inverse, used in ACLs and routing protocols (e.g., OSPF). The wildcard for 255.255.255.0 is 0.0.0.255.
RFC 2544 reserved for network device benchmarking. Clash/Mihomo's fake-ip mode uses 198.18.0.1/16 (a subset) as its fake IP pool by default โ these addresses are never routed on the public internet, avoiding conflicts with real traffic.
RFC 6598 reserved for Carrier-Grade NAT. If your public IP falls in this range, you're behind ISP-level NAT, which may affect P2P, port forwarding, and direct VPN connections. Tailscale/ZeroTier mesh VPNs also use this range.
Three private IP ranges not routed on the public internet: 10.0.0.0/8 (Class A, 16M addresses), 172.16.0.0/12 (Class B, 1M), 192.168.0.0/16 (Class C, 65K). Home routers typically use 192.168.x.x; enterprises and cloud VPCs use 10.x.x.x.
To split a large network into smaller subnets: โ Determine how many subnets and hosts per subnet you need; โก Borrow bits from the host portion (each borrowed bit doubles subnets, halves hosts); โข Calculate each subnet's network address and usable range. E.g., /24 split into 4x /26 gives 62 usable hosts each.
FAQ
Of 256 addresses, the first is the network address (e.g., 192.168.1.0) and the last is the broadcast (e.g., 192.168.1.255). These can't be assigned to hosts, so usable = 2^(32-prefix) - 2.
/31 (RFC 3021) is for point-to-point links โ only 2 addresses, no network/broadcast needed. Supported by Cisco/Juniper routers. /32 is a single host address, commonly used for loopback interfaces and routing policies.
Variable Length Subnet Masking allows different prefix lengths within the same network, maximizing IP utilization. E.g., server subnet uses /27 (30 hosts), office subnet uses /24 (254 hosts).