IPv4 range expander
Given a start and end IP, computes the minimal list of CIDR blocks covering that range — very practical when tidying firewall rules.
Given a start and an end IPv4 address, this tool calculates a valid IPv4 subnet along with its CIDR notation.
Steps and notes
What is IPv4 range expander?
Given a start and an end address, this tool finds the smallest CIDR block (or a minimal set of blocks) that covers the whole range. Useful when a firewall, cloud security group or routing table only accepts CIDR notation but your list of machines was defined by two endpoints.
- Enter the start IP
- Enter the end IP
- Read the generated CIDR list
- If the range is not a contiguous block it is split into several CIDRs — that is expected
Frequently asked questions
- Why is the result larger than my range?
- CIDR blocks must start on a boundary and have a power-of-two size. If your start and end are not aligned, the covering block necessarily includes extra addresses on both sides — the tool picks the smallest such block.
- Why did my range split into several CIDRs?
- Some ranges cannot be covered by a single block without huge waste. The tool then returns the minimal set of contiguous blocks that exactly covers your endpoints, which is still valid for firewall rules.
- What does /32 mean here?
- /32 is a block of exactly one address — start and end are the same. It is the tightest possible rule and often what you want when whitelisting a single host.
Category: Network
Network & IP workflow
IPv4 Subnet Calculator → IPv4 range expander → IPv4 address converter → IPv6 ULA generator → MAC address generator → MAC address lookup → WHOIS lookup