arping: Detect a Duplicate IP Address or Proxy ARP on Linux
Two MACs can answer for one IP while ping still works. Capture the duplicate, repair it, and test a Linux proxy that answers ARP but not DAD.
Linux Labs
Hands-on Linux networking labs built from network namespaces, veth links, and open-source tools. Each lab breaks one thing on purpose, captures the evidence, and verifies the fix.