server echoes back to the relay agent.
verbatim to the relay agent in server-to-client replies .
even if the server does not recognize them.
echoes back to the relay agent.
options that the server must echo back.
option-len               2 * number of requested options.
agent options in the Relay Forward message.
does not otherwise recognize that option.
23 of  provides general DHCPv6 security considerations.
Agent Echo Request) Option (43).