.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH IPV6_V6ONLY 2const 2026-01-05 "Linux man-pages 6.17"
.SH NAME
IPV6_V6ONLY
\-
restrict to IPv6 only
.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_IP,\~IPV6_V6ONLY,
.BI "               const\~int\~*" enable ,\~sizeof(int));
.fi
.SH DESCRIPTION
.\" See RFC 3493
If this flag is set to true (nonzero),
then the socket is restricted
to sending and receiving IPv6 packets only.
In this case,
an IPv4 and an IPv6 application can bind
to a single port at the same time.
.P
If this flag is set to false (zero),
then the socket can be used to send and receive packets
to and from an IPv6 address or an IPv4-mapped IPv6 address.
.P
The default value for this flag is defined by the contents of the file
.IR /proc/sys/net/ipv6/bindv6only .
The default value for that file is 0 (false).
.\" FLOWLABEL_MGR, FLOWINFO_SEND
.SH ERRORS
See
.BR IPPROTO_IPV6 (2const).
See
.BR setsockopt (2).
See
.BR ipv6 (7).
.SH HISTORY
POSIX.1-2001,
Linux 2.4.21, Linux 2.6.
.SH SEE ALSO
.BR IPPROTO_IPV6 (2const),
.BR setsockopt (2),
.BR ipv6 (7)