.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH IPV6_ROUTER_ALERT 2const 2025-12-02 "Linux man-pages 6.17"
.SH NAME
IPV6_ROUTER_ALERT
\-
pass forwarded packets containing a router alert hop-by-hop to this 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_IPV6,\~IPV6_ROUTER_ALERT,
.BI "               const\~int\~*" val ,\~sizeof(int));
.fi
.SH DESCRIPTION
Pass forwarded packets containing a router alert hop-by-hop option to
this socket.
.P
Allowed only for
.B SOCK_RAW
sockets.
.P
The tapped packets are not forwarded by the kernel,
it is the user's responsibility to send them out again.
.P
A positive integer indicates a router alert option value to intercept.
Packets carrying a router alert option
with a value field containing this integer
will be delivered to the socket.
A negative integer disables delivery of packets
with router alert options
to this socket.
.SH ERRORS
See
.BR IPPROTO_IPV6 (2const).
See
.BR setsockopt (2).
See
.BR ipv6 (7).
.SH SEE ALSO
.BR IPPROTO_IPV6 (2const),
.BR setsockopt (2),
.BR cmsg (3),
.BR ipv6 (7)