.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH IP_MULTICAST_TTL 2const 2025-11-25 "Linux man-pages 6.17"
.SH NAME
IP_MULTICAST_TTL
\-
time-to-live value of outgoing multicast packets
.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_TTL,
.BI "               const\~int\~*" ttl ,\~sizeof(int));
.BI int\~getsockopt(int\~ sockfd ,\~IPPROTO_IP,\~IP_MULTICAST_TTL,
.BI "               int\~*" ttl ,\~sizeof(int));
.fi
.SH DESCRIPTION
Set or read the time-to-live value of outgoing multicast packets for this
socket.
.P
The default is 1 which means that multicast packets don't leave the local
network unless the user program explicitly requests it.
.SH ERRORS
See
.BR IPPROTO_IP (2const).
See
.BR setsockopt (2).
See
.BR ip (7).
.SH HISTORY
Linux 1.2.
.SH CAVEATS
It is very important for multicast packets to set the smallest TTL possible.
.SH SEE ALSO
.BR IPPROTO_IP (2const),
.BR setsockopt (2),
.BR ip (7)