IP Overlap Checker
One CIDR block per line, IPv4 and IPv6 mixed. Checked in your browser.
5 networks checked.
Overlapping pairs 3
- 10.0.0.0/16 appears more than once#1 · #5
- 10.0.0.0/16 contains 10.0.128.0/20#1 · #2
- 10.0.0.0/16 contains 10.0.128.0/20#5 · #2
Merged list (2)
The smallest set of CIDR blocks that covers exactly the same addresses.
10.0.0.0/16 192.168.0.0/24
Overlapping networks cause some of the most confusing faults in practice: two VPN sites that both use 10.0.0.0/16, a cloud subnet that collides with an office LAN, or a firewall rule that silently shadows another.
Paste your networks one per line. CIDR blocks can only nest or be disjoint, so every overlap the tool reports is one of two kinds: the same block listed twice, or one block containing another. The check runs in your browser in a single pass, so lists of several thousand blocks are fine.
The merged list is the smallest set of CIDR blocks that covers exactly the same addresses: duplicates and contained blocks disappear and adjacent blocks are joined where they line up (10.0.0.0/25 and 10.0.0.128/25 become 10.0.0.0/24). It is the list you would put in a route filter or an allowlist.
Frequently asked questions
Why was my entry changed?
An entry with host bits set, such as 10.1.2.3/16, describes the network 10.1.0.0/16. The tool shows the network it was read as.
Can I mix IPv4 and IPv6?
Yes. They are checked separately, since an IPv4 block can never overlap an IPv6 block.
Is anything sent to the server?
No. The calculation runs entirely in your browser.