Cisco Systems, Inc Ericsson Struik Security Consultancy This document updates the 6LoWPAN Neighbor Discovery (ND) protocol defined in RFC 6775 and RFC 8505. The new extension is called Address Protected Neighbor Discovery (AP-ND) and it protects the owner of an address against address theft and impersonation attacks in a low-power and lossy network (LLN). Nodes supporting this extension compute a cryptographic identifier (Crypto-ID) and use it with one or more of their Registered Addresses. The Crypto-ID identifies the owner of the Registered Address and can be used to provide proof of ownership of the Registered Addresses. Once an address is registered with the Crypto-ID and a proof-of-ownership is provided, only the owner of that address can modify the registration information, thereby enforcing Source Address Validation.