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/*
* Copyright 1994, 1995 Massachusetts Institute of Technology
*
* Permission to use, copy, modify, and distribute this software and
* its documentation for any purpose and without fee is hereby
* granted, provided that both the above copyright notice and this
* permission notice appear in all copies, that both the above
* copyright notice and this permission notice appear in all
* supporting documentation, and that the name of M.I.T. not be used
* in advertising or publicity pertaining to distribution of the
* software without specific, written prior permission. M.I.T. makes
* no representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied
* warranty.
*
* THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
* ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
* SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
/*
* This is a simple program which demonstrates how to query the kernel
* routing mechanism using only a UDP socket. Pass it a hostname on
* the command line (sorry, it doesn't parse dotted decimal) and it will
* print out an IP address which names the interface over which UDP
* packets intended for that destination would be sent.
* A more sophisticated program might use the list obtained from SIOCGIFCONF
* to match the address with an interface name, but applications programmers
* much more often need to know the address of the interface rather than
* the name.
*/
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <netdb.h>
#include <err.h>
#include <errno.h>
#include <string.h>
#include <sysexits.h>
int
main(int argc, char **argv)
{
struct sockaddr_in local, remote;
struct hostent *hp;
int s, rv, namelen;
argc--, argv++;
if (!*argv) {
errx(EX_USAGE, "must supply a hostname");
}
hp = gethostbyname(*argv);
if (!hp) {
errx(EX_NOHOST, "cannot resolve hostname: %s", *argv);
}
memcpy(&remote.sin_addr, hp->h_addr_list[0], sizeof remote.sin_addr);
remote.sin_port = htons(60000);
remote.sin_family = AF_INET;
remote.sin_len = sizeof remote;
local.sin_addr.s_addr = htonl(INADDR_ANY);
local.sin_port = htons(60000);
local.sin_family = AF_INET;
local.sin_len = sizeof local;
s = socket(PF_INET, SOCK_DGRAM, 0);
if (s < 0)
err(EX_OSERR, "socket");
do {
rv = bind(s, (struct sockaddr *)&local, sizeof local);
local.sin_port = htons(ntohs(local.sin_port) + 1);
} while(rv < 0 && errno == EADDRINUSE);
if (rv < 0)
err(EX_OSERR, "bind");
do {
rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
remote.sin_port = htons(ntohs(remote.sin_port) + 1);
} while(rv < 0 && errno == EADDRINUSE);
if (rv < 0)
err(EX_OSERR, "connect");
namelen = sizeof local;
rv = getsockname(s, (struct sockaddr *)&local, &namelen);
if (rv < 0)
err(EX_OSERR, "getsockname");
printf("Route to %s is out %s\n", *argv, inet_ntoa(local.sin_addr));
return 0;
}
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