This feature makes a switch act as a neighbor discovery proxy for an IPv6 subnets. It can be used in conjunction with BUM

IPv6 Duplicate Address Detection Proxy is a proxy-based mechanism allowing the use of Duplicate Address Detection (DAD) by IPv6 nodes in a point-to-multipoint architecture with a "split-horizon" forwarding scheme. In Split-horizon scenario where the hosts can not directly communicate with each other, but only through a BNG (Broadband Network Gateway). 

Proxy IPv6 ND EOS 4.32.0F