CIDR Range Expander

Enumerate IPv4 addresses from a CIDR block with explicit boundary and output-size controls.

IPv4 CIDR block

A host address inside the block is accepted; output is normalized to the block's prefix boundary.

Choose what gets emitted

Output format

Expansion safety limit

Address count is checked before any list is allocated. Output above 65,536 addresses is refused so a broad prefix cannot freeze the page.

Include prefix-base and broadcast boundaries for /0–/30/31 point-to-point prefixes keep both endpoints, and /32 always keeps its single address.Show subnet detailsKeep masks, boundaries, counts, and the normalized CIDR visible beside the generated list.

Expanded IP output

Expanded IPv4 addresses will appear here.

Expansion is local browser arithmetic. The CIDR value is not sent to a network service.

A CIDR block is compact; an address list is not

192.168.1.0/29 describes eight IPv4 addresses in a few characters. Expanding that block is useful when an allowlist, audit, spreadsheet, or script needs individual values rather than a prefix.

The size doubles every time the prefix becomes one bit shorter. A /16 already contains 65,536 addresses; a /8 contains more than sixteen million. That growth is why the page refuses oversized output before constructing it.

Boundary addresses are a policy choice, not just a checkbox

Traditional IPv4 subnets from /0 through /30 normally keep the prefix-base address for the subnet itself and the all-ones host address for directed broadcast. Excluding those two values is therefore a sensible default for a generic host list.

/31 is different. RFC 3021 permits both addresses as endpoints on a point-to-point link, so neither is removed here. /32 represents one address and is emitted as one address. RFC 3021 covers the /31 exception.

Why the input is normalized

10.0.0.37/24 and 10.0.0.0/24 describe the same /24 block. Host bits are cleared before expansion so the list always matches the actual prefix boundary.

What CIDR itself standardizes

RFC 4632 documents the IPv4 CIDR addressing and aggregation model. Expansion into a text, CSV, or JSON list is an application convenience rather than part of the CIDR standard. Read RFC 4632.

Output formats have different downstream expectations

Line list

One IP per line works well for simple allowlists, shell input, and visual review.

CSV

A single column named ip with CRLF rows is easier to import into spreadsheets and data tools than one comma-packed line.

JSON array

Quoted string values preserve each address cleanly for application configuration and scripts.