Loading page
About this tool
Convert between CIDR notation, start-end IP ranges and Cisco wildcard masks in bulk, with minimal CIDR splitting for arbitrary ranges.
This converter translates IPv4 networks between their three common notations — CIDR blocks (RFC 4632), start–end address ranges and Cisco ACL wildcard masks — in bulk, one entry per line. Arbitrary ranges that do not align to a power-of-two boundary are decomposed into the minimal list of CIDR blocks using the standard greedy alignment algorithm, and non-contiguous wildcard masks are detected and rejected with an explanation. It is built for network and cloud engineers moving allowlists between firewalls, ACLs and cloud security groups that each demand a different format.
Open CIDR to IP Range Converter on AltFTool — it loads instantly in your browser.
Paste or upload your source content.
Choose the target format or conversion mode.
Copy or download the converted result.
Every line is shown as a range, as CIDR block(s) and — when exact — as a wildcard entry.
Unaligned ranges are decomposed into the fewest possible blocks, never one-per-address.
Non-contiguous wildcard masks are flagged instead of being silently misconverted.
If the range starts on a power-of-two boundary and its length is a power of two, it is a single CIDR: 10.0.0.0–10.0.0.255 is 10.0.0.0/24. Otherwise it must be split: the greedy algorithm repeatedly takes the largest block that starts at the current address and fits the remainder, so 10.0.0.5–10.0.0.16 becomes 10.0.0.5/32, 10.0.0.6/31, 10.0.0.8/29 and 10.0.0.16/32.
A wildcard mask is the bitwise inverse of the subnet mask: /24 has subnet mask 255.255.255.0 and wildcard 0.0.0.255. Wildcards are used in Cisco ACLs and OSPF network statements, where 0 bits mean 'must match' and 1 bits mean 'ignore'. Unlike subnet masks, wildcards may legally be non-contiguous, in which case they match a scattered set that no single CIDR can represent.
CIDR blocks are always a power-of-two in size and start at a multiple of that size. A range like 10.0.0.5–10.0.0.16 holds 12 addresses starting at an odd offset, so no single prefix covers exactly those addresses — it takes four blocks. This tool always emits the provably minimal set.
2^(32 − prefix): a /24 holds 256 addresses, a /16 holds 65,536 and a /8 holds 16,777,216. That count includes the network and broadcast addresses; usable host counts are two lower on ordinary subnets (see a subnet calculator for /31 and /32 special cases).
Add the CIDR to IP Range Converterwidget to your blog or website — free, responsive, no signup. Just keep the “Widget by AltFTool” credit link visible.
<iframe src="https://www.altftool.com/embed/widget/cidr-to-ip-range-converter"
title="CIDR to IP Range Converter — free AltFTool widget"
width="100%" height="640" style="border:0;border-radius:12px;overflow:hidden"
loading="lazy" referrerpolicy="no-referrer-when-downgrade"></iframe>
<p style="font-size:12px;margin:4px 0 0">Widget by <a href="https://www.altftool.com/tools/all/cidr-to-ip-range-converter?utm_source=embed&utm_medium=widget">AltFTool — free online tools</a></p>