Function in_canforward

freebsd/netinet/in.c:195–204

* Determine whether an IP address is in a reserved set of addresses * that may not be forwarded, or whether datagrams to that destination * may be forwarded. */

 * may be forwarded.
 */
int
in_canforward(struct in_addr in)
{
	u_long i = ntohl(in.s_addr);

	if (IN_EXPERIMENTAL(i) || IN_MULTICAST(i) || IN_LINKLOCAL(i) ||
	    IN_ZERONET(i) || IN_LOOPBACK(i))
		return (0);
	return (1);
}

/*
 * Trim a mask in a sockaddr