SubnetSleuth

SubnetSleuth is a web + lightweight desktop agent app that continuously maps what IPs are actually in use across your subnets and flags mismatches against your intended IP plan. It focuses on the ugly, common reality: stale spreadsheets, DHCP reservations that drift, shadow IT devices, and “temporary” static IPs that become permanent. The agent passively listens (ARP/NDP, DHCP logs, switch MAC tables via SNMP) and correlates identities (MAC, hostname, vendor, last-seen) to an authoritative inventory. You get alerts for duplicate IPs, unexpected static assignments inside DHCP pools, new devices appearing on restricted VLANs, and subnets nearing exhaustion. It also generates a clean, exportable IP utilization report for audits and change reviews. This is not a full IPAM replacement; it’s a pragmatic “truth layer” that sits on top of whatever you already use and catches what your tools miss.