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Subnet Calculator

v2.10.0

IP Address?Enter an IPv4 address (e.g. 192.168.1.1) or CIDR notation (e.g. 192.168.1.0/24). The subnet mask field is optional when using CIDR notation.

Netmask?Enter the subnet mask as a prefix length (/24), dotted-decimal (255.255.255.0), or wildcard (0.0.0.255). Leave blank when using CIDR notation in the IP field.

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Split Subnet

Split into?Enter a prefix length larger than the parent (e.g. /25 splits a /24 into two /25 subnets). The result is capped at the configured maximum.

Supernet & Route Summarisation

?Finds the smallest single CIDR block that contains all of the listed CIDRs. Useful for aggregating routes into a single summary route. ?Computes the minimal set of non-overlapping CIDRs that exactly covers the listed networks. Unlike Find Supernet, this avoids including addresses outside the input ranges.

IP Range → CIDR?Enter a start and end IPv4 address to get the minimal set of CIDR blocks that exactly covers that range using the greedy largest-aligned-block algorithm.

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Subnet Allocation Tree

Parent CIDR

Wildcard ↔ CIDR?Bidirectional Cisco-style converter. Enter a wildcard mask (e.g. 0.0.0.255) to get its CIDR prefix, or a prefix (/24 or 24) to get the wildcard. Non-contiguous masks are rejected.

IPv6 Address

Prefix

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Tool

Split Subnet

Split into?Enter a prefix length larger than the parent (e.g. /65 splits a /64 into two /65 subnets). The result is capped at the configured maximum.

IPv6 ULA Prefix Generator (RFC 4193)

Global ID (optional 10 hex chars)?A 40-bit hex value used as the globally unique portion of the ULA prefix (RFC 4193). Leave blank to generate one pseudo-randomly from the current timestamp.

Parent Network

Prefix

Name Hosts Needed

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Tool

Subnet Overlap Checker?Compares two CIDRs and reports whether they overlap, one contains the other, are identical, or have no relationship. Supports both IPv4 and IPv6.

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Multi-CIDR Overlap Check?Enter up to 50 IPv4 or IPv6 CIDRs, one per line. The tool reports any pairs that overlap, are identical, or where one contains the other.

github.com/seanmousseau/Subnet-Calculator · Docs

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