Reverse Subnet Lookup
"What subnet is this IP in?" — check an address against a list of known networks
Reverse Lookup
Paste your known networks below (one CIDR per line) and check which ones contain a given IPv4 address. Handy for troubleshooting which VLAN/subnet an address belongs to.
| Network | Prefix | Result |
|---|
How the match is decided
For each network line, the tool ANDs your target IP with that network's subnet mask and compares it to the network address — if they match, the IP falls inside that block. When several networks overlap and all contain the address, the one with the longest prefix (most specific, e.g. /26 over /24) is marked as the best match — the same longest-prefix-match rule real routers use.