Proxy NDP is router behavior in which a router answers IPv6 Neighbor Discovery messages for another host. It matters because IPv4 proxy ARP has no equivalent on Cisco routers. section 21.3.1 section 21.4
This limitation breaks directly connected IPv6 static routes on Ethernet. The route can appear valid, yet the router cannot resolve the remote host’s MAC address and drops packets. section 21.3.1
PC1-to-PC3 failure
R1 routes 2001:db8:3::/64 out G0/0 and shows the route as directly connected. A ping to PC3 fails because R1’s neighbor table remains INCMP: R2 does not answer the Neighbor Solicitation for PC3. section 21.3.1
R1# show ipv6 neighbors IPv6 Address Age Link-layer Addr State Interface 2001:DB8:3::13 0 - INCMP Gi0/0 #1 . . . #1 PC3’s entry is incomplete.
Inspect the INCMP neighbor entry that reveals why the apparently valid Ethernet route cannot forward traffic. section 21.3.1
