.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH IP_MULTICAST_IF 2const 2025-11-25 "Linux man-pages 6.17"
.SH NAME
IP_MULTICAST_IF
\-
local device for a multicast socket
.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,\~IP_MULTICAST_IF,
.BI "               const\~void\~" val [ size ],\~size_t\~ size );
.BI int\~getsockopt(int\~ sockfd ,\~IPPROTO_IP,\~IP_MULTICAST_IF,
.BI "               struct\~in_addr\~*" val ,\~sizeof(struct\~in_addr));
.fi
.SH DESCRIPTION
Set the local device for a multicast socket.
.P
The argument for
.BR setsockopt (2)
is an
.BR ip_mreqn (2type)
or
.\" net: IP_MULTICAST_IF setsockopt now recognizes struct mreq
.\" Commit: 3a084ddb4bf299a6e898a9a07c89f3917f0713f7
(since Linux 3.5)
.BR ip_mreq (2type)
structure,
or an
.BR in_addr (2type)
structure.
(The kernel determines which structure is being passed based
on the size passed in
.IR size .)
.SH ERRORS
See
.BR IPPROTO_IP (2const).
See
.BR setsockopt (2).
See
.BR ip (7).
.SH HISTORY
Linux 1.2.
.SH SEE ALSO
.BR IPPROTO_IP (2const),
.BR in_addr (2type),
.BR ip_mreqn (2type),
.BR setsockopt (2),
.BR ip (7)