.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH IPV6_ADDRFORM 2const 2025-12-02 "Linux man-pages 6.17"
.SH NAME
IPV6_ADDRFORM
\-
turn an AF_INET6 socket into a socket of a different address family
.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,\~IPV6_ADDRFORM,
.B "               &(const\~int){AF_INET},\~sizeof(int));"
.fi
.SH DESCRIPTION
Turn an
.B AF_INET6
socket into a socket of a different address family.
.P
Only
.B AF_INET
is currently supported for that.
.P
It is allowed only for IPv6 sockets
that are connected and bound to a v4-mapped-on-v6 address.
.P
This is useful to pass v4-mapped sockets as file descriptors to
programs that don't know how to deal with the IPv6 API.
.SH ERRORS
See
.BR setsockopt (2).
See
.BR ipv6 (7).
.SH SEE ALSO
.BR IPPROTO_IPV6 (2const),
.BR setsockopt (2),
.BR ipv6 (7)