.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" The following socket options are undocumented
.\"	All of the following are from:
.\"	    commit 333fad5364d6b457c8d837f7d05802d2aaf8a961
.\"	    Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
.\"	    Support several new sockopt / ancillary data in Advanced API (RFC3542).
.\"		IPV6_2292PKTINFO (2.6.14)
.\"		    Formerly IPV6_PKTINFO
.\"		IPV6_2292HOPOPTS (2.6.14)
.\"		    Formerly IPV6_HOPOPTS, which is documented
.\"		IPV6_2292DSTOPTS (2.6.14)
.\"		    Formerly IPV6_DSTOPTS, which is documented
.\"		IPV6_2292RTHDR (2.6.14)
.\"		    Formerly IPV6_RTHDR, which is documented
.\"		IPV6_2292PKTOPTIONS (2.6.14)
.\"		    Formerly IPV6_PKTOPTIONS
.\"		IPV6_2292HOPLIMIT (2.6.14)
.\"		    Formerly IPV6_HOPLIMIT, which is documented
.\"
.\"		IPV6_RECVHOPLIMIT (2.6.14)
.\"		IPV6_RECVHOPOPTS (2.6.14)
.\"		IPV6_RTHDRDSTOPTS (2.6.14)
.\"		IPV6_RECVRTHDR (2.6.14)
.\"		IPV6_RECVDSTOPTS (2.6.14)
.\"
.\"	IPV6_RECVPATHMTU (Linux 2.6.35, flag value added in Linux 2.6.14)
.\"	    commit 793b14731686595a741d9f47726ad8b9a235385a
.\"	    Author: Brian Haley <brian.haley@hp.com>
.\"	IPV6_PATHMTU (Linux 2.6.35, flag value added in Linux 2.6.14)
.\"	    commit 793b14731686595a741d9f47726ad8b9a235385a
.\"	    Author: Brian Haley <brian.haley@hp.com>
.\"	IPV6_DONTFRAG (Linux 2.6.35, flag value added in Linux 2.6.14)
.\"	    commit 793b14731686595a741d9f47726ad8b9a235385a
.\"	    Author: Brian Haley <brian.haley@hp.com>
.\"	    commit 4b340ae20d0e2366792abe70f46629e576adaf5e
.\"	    Author: Brian Haley <brian.haley@hp.com>
.\"
.\"	IPV6_RECVTCLASS (Linux 2.6.14)
.\"	    commit 41a1f8ea4fbfcdc4232f023732584aae2220de31
.\"	    Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
.\"		Based on patch from David L Stevens <dlstevens@us.ibm.com>
.\"
.\"	IPV6_CHECKSUM (Linux 2.2)
.\"	IPV6_NEXTHOP (Linux 2.2)
.\"	IPV6_JOIN_ANYCAST (Linux 2.4.21 / Linux 2.6)
.\"	IPV6_LEAVE_ANYCAST (Linux 2.4.21 / Linux 2.6)
.\"	IPV6_FLOWLABEL_MGR (Linux 2.2.7 / Linux 2.4)
.\"	IPV6_FLOWINFO_SEND (Linux 2.2.7 / Linux 2.4)
.\"	IPV6_IPSEC_POLICY (Linux 2.6)
.\"	IPV6_XFRM_POLICY (Linux 2.6)
.\"	IPV6_TCLASS (Linux 2.6)
.\"
.\"	IPV6_ADDR_PREFERENCES (Linux 2.6.26)
.\"	    commit 7cbca67c073263c179f605bdbbdc565ab29d801d
.\"	    Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
.\"	IPV6_MINHOPCOUNT (Linux 2.6.35)
.\"	    commit e802af9cabb011f09b9c19a82faef3dd315f27eb
.\"	    Author: Stephen Hemminger <shemminger@vyatta.com>
.\"	IPV6_ORIGDSTADDR (Linux 2.6.37)
.\"	    Actually a CMSG rather than a sockopt?
.\"	    In header file, we have IPV6_RECVORIGDSTADDR == IPV6_ORIGDSTADDR
.\"	    commit 6c46862280c5f55eda7750391bc65cd7e08c7535
.\"	    Author: Balazs Scheidler <bazsi@balabit.hu>
.\"	IPV6_RECVORIGDSTADDR (Linux 2.6.37)
.\"	    commit 6c46862280c5f55eda7750391bc65cd7e08c7535
.\"	    Author: Balazs Scheidler <bazsi@balabit.hu>
.\"	        Support for IPV6_RECVORIGDSTADDR sockopt for UDP sockets
.\"		were contributed by Harry Mason.
.\"	IPV6_TRANSPARENT (Linux 2.6.37)
.\"	    commit 6c46862280c5f55eda7750391bc65cd7e08c7535
.\"	    Author: Balazs Scheidler <bazsi@balabit.hu>
.\"	IPV6_UNICAST_IF (Linux 3.4)
.\"	    commit c4062dfc425e94290ac427a98d6b4721dd2bc91f
.\"	    Author: Erich E. Hoover <ehoover@mines.edu>
.\"
.TH IPPROTO_IPV6 2const 2026-01-05 "Linux man-pages 6.17"
.SH NAME
IPPROTO_IPV6
\-
Linux IPv6 protocol socket options
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#include <netinet/in.h>" "  /* Definition of " IP* " constants */"
.B #include <sys/socket.h>
.P
.BI int\~setsockopt(int\~ sockfd ,\~IPPROTO_IPV6,\~int\~ opt ,
.BI "               const\~void\~" val [ size ],\~size_t\~ size );
.BI int\~getsockopt(int\~ sockfd ,\~IPPROTO_IPV6,\~int\~ opt ,
.BI "               void\~" val [ size ],\~size_t\~ size );
.fi
.SH DESCRIPTION
IPv6 supports some protocol-specific socket options that can be set with
.BR setsockopt (2)
and read with
.BR getsockopt (2).
The socket option level for IPv6 is
.BR IPPROTO_IPV6 .
A boolean integer flag is zero when it is false, otherwise true.
.P
The following socket options are supported.
.TP
.BR IPV6_ADDRFORM (2const)
.TQ
.BR IPV6_ADD_MEMBERSHIP (2const)
.TQ
.BR IPV6_DROP_MEMBERSHIP (2const)
.TQ
.BR IPV6_MTU (2const)
.TQ
.BR IPV6_MTU_DISCOVER (2const)
.TQ
.BR IPV6_MULTICAST_HOPS (2const)
.TQ
.BR IPV6_MULTICAST_IF (2const)
.TQ
.BR IPV6_MULTICAST_LOOP (2const)
.TQ
.BR IPV6_RECVPKTINFO (2const)
.TQ
.BR IPV6_RTHDR (2const)
.TQ
.BR IPV6_AUTHHDR (2const)
.TQ
.BR IPV6_DSTOPTS (2const)
.TQ
.BR IPV6_HOPOPTS (2const)
.TQ
.BR IPV6_FLOWINFO (2const)
.TQ
.BR IPV6_HOPLIMIT (2const)
.TQ
.BR IPV6_RECVERR (2const)
.TQ
.BR IPV6_ROUTER_ALERT (2const)
.TQ
.BR IPV6_UNICAST_HOPS (2const)
.TQ
.BR IPV6_V6ONLY (2const)
.SH ERRORS
See
.BR setsockopt (2).
See
.BR ipv6 (7).
.TP
.B ENOPROTOOPT
.I opt
is invalid.
.SH HISTORY
.TP
.B IPPROTO_IPV6
POSIX.1-2001.
.SH SEE ALSO
.BR setsockopt (2),
.BR cmsg (3),
.BR ipv6 (7)