CIDR to IP Range
Convert between CIDR notation and IP ranges. Supports IPv4 and IPv6. Aggregate multiple ranges into minimal CIDR blocks.
192.168.1.0/24
- Network
- 192.168.1.0
- Broadcast
- 192.168.1.255
- First usable
- 192.168.1.1
- Last usable
- 192.168.1.254
- Prefix
- /24
- Total
- 256
About this tool
CIDR (Classless Inter-Domain Routing) notation — a block like
192.168.1.0/24 — replaced the old A/B/C address classes
in 1993. It is the native format for routing tables, firewall rules,
and ACLs on every modern network device. But humans often think in
ranges (192.168.1.0 through 192.168.1.255),
and some input forms (security audit reports, CSV exports from
scanning tools, geo-IP feeds) give ranges rather than CIDR. This tool
converts in both directions, for both IPv4 and IPv6.
CIDR → range mode is the common case: paste one or
more CIDR blocks and see the first and last addresses, total size,
and (for IPv4) the broadcast and first/last usable hosts.
Range → CIDR mode takes a dash-separated range and
finds the minimal set of CIDR blocks that cover it. For an aligned
range like 10.0.0.0 - 10.0.255.255, that is a single
/16. For an arbitrary range, it may be a list of
different-sized blocks — the greedy algorithm always finds the
shortest list.
CIDR aggregation is used everywhere in networking: BGP route
summarization, firewall rule compaction, WAF allow-list maintenance,
and cloud VPC peering. A smaller CIDR list means fewer rules to
evaluate, which improves performance and reduces the chance of
misconfiguration. If you have fifty individual /32 IPs
that turn out to be contiguous, aggregating them to a single
/24 replaces fifty rules with one.
For IPv6, the tool uses BigInt arithmetic to handle the
128-bit address space accurately. Aggregation math is identical to
IPv4 in principle; the prefix lengths are simply larger. A single
/64 IPv6 range fits eighteen quintillion
addresses, so the "total" column uses scientific notation for blocks
with prefixes shorter than /110 or so.
Bulk mode: paste many CIDRs or ranges at once,
one per line. Comments starting with # are ignored. This
is useful for auditing exported firewall rules, cloud security
groups, or geo-IP allow-lists.
Frequently asked questions
When should I use CIDR vs an explicit IP range?
CIDR is preferred for firewall rules, routing tables, and access control lists because most network tooling accepts CIDR directly. Explicit ranges are more human-friendly for documentation and for ranges that do not align to a power-of-two boundary. The tool converts between the two so you can use whichever fits the system you are configuring.
What are the RFC 1918 private ranges?
10.0.0.0/8 (16,777,216 addresses), 172.16.0.0/12 (1,048,576 addresses), and 192.168.0.0/16 (65,536 addresses). Any IP outside these, plus the loopback 127.0.0.0/8, link-local 169.254.0.0/16, and carrier-grade NAT 100.64.0.0/10, is either public or reserved. The tool does not flag RFC 1918 ranges specifically here — use the Subnet Calculator for that.
What is the difference between a supernet and a subnet?
A supernet is a larger block formed by combining two or more smaller blocks. A subnet is a smaller block carved out of a larger one. If 192.168.0.0/24 and 192.168.1.0/24 are combined, the supernet is 192.168.0.0/23. This tool aggregates adjacent ranges into their shortest-possible CIDR list via greedy algorithm.
Why is /31 special?
In classical IPv4, a /31 has only two addresses — the network and the broadcast — leaving no usable hosts. RFC 3021 (from 2000) reallocated /31 for point-to-point links between routers: both addresses are usable, since no broadcast is needed on a two-host segment. This tool reflects that: /31 reports two usable addresses, not zero.
How does CIDR work for IPv6?
Exactly the same way — the prefix tells you how many leading bits identify the network. The difference is scale: IPv6 prefixes range from /0 to /128, and a "normal" end-user subnet is /64 (same size as the entire IPv4 Internet, squared). Aggregation and range conversion use the same algorithm as IPv4, just with 128-bit arithmetic.