IP_ROUTER_ALERT(2const)                                IP_ROUTER_ALERT(2const)

NAME
       IP_ROUTER_ALERT - pass all to-be forwarded packets

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <netinet/in.h>  /* Definition of IP* constants */
       #include <sys/socket.h>

       int setsockopt(int sockfd, IPPROTO_IP, IP_ROUTER_ALERT,
                      const int *enable, sizeof(int));

DESCRIPTION
       Pass all to-be forwarded packets with the IP Router Alert option set to
       this socket.

       Valid only for raw sockets.

       This is useful, for instance, for user-space RSVP daemons.

ERRORS
       See IPPROTO_IP(2const).  See setsockopt(2).  See ip(7).

STANDARDS
       Linux.

HISTORY
       Linux 2.2.

CAVEATS
       The tapped packets are not forwarded by the kernel; it is the user's
       responsibility to send them out again.

       Socket binding is ignored, such packets are filtered only by protocol.

SEE ALSO
       IPPROTO_IP(2const), setsockopt(2), ip(7)

Linux man-pages 6.17              2025-11-25           IP_ROUTER_ALERT(2const)