Contifield

Text and developer tools

IPv4 and IPv6 CIDR overlap checker

Compare two IPv4 or IPv6 network prefixes for overlap, containment, equality or adjacency with exact address ranges and counts.

Runs in your browser. Inputs stay on this page and are not uploaded or added to the URL.

IPv4 /0–/32 or IPv6 /0–/128. Host bits are cleared to the containing network.
At most 80 characters per entry. Use a numeric prefix, without a URL, port, zone or brackets.

How to use this tool

Enter two address/prefix pairs. The checker normalizes host bits to network boundaries, then shows whether the ranges are equal, one contains the other, or they are disjoint. Adjacent ranges touch at consecutive addresses but do not overlap. For aligned CIDR prefixes, any intersection is the smaller contained network.

Both IPv4 and IPv6 support their full prefix ranges, including /0 and single-address /32 or /128. IPv6 accepts hexadecimal groups, one :: compression and an optional dotted IPv4 tail. Display uses lowercase, the longest zero run and the leftmost run when tied; a single zero group is not compressed. IPv4-mapped addresses use ::ffff:dotted-decimal notation.

IPv4 and IPv6 remain separate address families. Comparing an IPv4 block with an IPv4-mapped IPv6 block reports different families rather than inventing a mapping. Counts include all addresses in each prefix and do not represent usable hosts, allocated addresses or reachable services. All arithmetic stays in your browser; no network probes are made.

Worked example

2001:db8::1/32 normalizes to 2001:db8::/32 and contains 2001:db8:1234::/48. For IPv4, 192.0.2.0/25 and 192.0.2.128/25 are adjacent, with zero shared addresses.

References and method

Contifield is an independent utility site. Reference publishers do not endorse this tool.

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