BD I think that the correct answer there should be SOLICIT Packet, based on the For-way Negotiation (SARR). Before it will send a REQUEST packet to a DHCPv6 server, it should've sent a SOLICIT packet. But NS and RS could also be seem correct from a IPv6 node(client) context, prior to the allocation of addresses, it should be clearly understood that an IPv6 node(client) is required to generate a link-local address and be successfullly evaluated by the Duplicate Address Detection (DAD) process (NS & NA). Following this, a link router discovery process is involved, for which the IPv6 client node broadcast a Router Solicitation(RS) message, and the link router responds with a Router Advertisment(RA) message after receiving the RS message.