Ancillary Data for the advanced API

Use via msg_control data or socket options.

IPV6_PKTINFO, IPV6_RECVPKTINFO
Specifying/Receiving the Interface.
Specifying/Receiving source/destination address
IPV6_PKTINFO, IPV6_RECVPKTINFO
Specifying/Receiving the hop limit.
IPV6_RTHDR, IPV6_RECVRTHDR
Specifying/Receiving IPv6 routing headers.
IPV6_HOPOPTS, IPV6_RECVHOPOPTS
Specifying/Receiving IPv6 hop-by-hop options headers.
IPV6_DSTOPTS, IPV6_RECVDSTOPTS
Specifying/Receiving IPv6 destination options headers.
and more...(see the spec)