All tools on CIDRGen
Everything on this site runs 100% in your browser. No uploads, no accounts, nothing sent anywhere.
CIDRGen (main tool)
Free, 100% client-side CIDR subnet calculator. Network and broadcast addresses, usable ranges, netmask and wildcard, special-range detection, for IPv4 and IPv6 prefixes.
Subnet Splitter
Split an IPv4 CIDR block into equal smaller subnets: choose the new prefix and get every network with its usable host count. Runs in your browser.
CIDR Overlap Checker & Aggregator
Paste a list of IPv4 CIDR blocks to find overlaps and containment, spot entries that are not network addresses, and get the smallest set of blocks that covers them. Runs in your browser.
Netmask, Prefix and Wildcard Converter
Convert between a prefix length (/26), a dotted netmask (255.255.255.192) and an ACL wildcard (0.0.0.63). Rejects non-contiguous masks. Runs in your browser.
Looking for explanations rather than a tool? CIDRGen guides cover 3 worked examples and gotchas.
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