IP_ROUTER_ALERT(2const) IP_ROUTER_ALERT(2const)

IP_ROUTER_ALERT - pass all to-be forwarded packets

Standard C library (libc-lc)

#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));

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.

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

Linux.

Linux 2.2.

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.

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

2025-11-25 Linux man-pages 6.17