1 /* 2 * Copyright 1994, 1995 Massachusetts Institute of Technology 3 * 4 * Permission to use, copy, modify, and distribute this software and 5 * its documentation for any purpose and without fee is hereby 6 * granted, provided that both the above copyright notice and this 7 * permission notice appear in all copies, that both the above 8 * copyright notice and this permission notice appear in all 9 * supporting documentation, and that the name of M.I.T. not be used 10 * in advertising or publicity pertaining to distribution of the 11 * software without specific, written prior permission. M.I.T. makes 12 * no representations about the suitability of this software for any 13 * purpose. It is provided "as is" without express or implied 14 * warranty. 15 * 16 * THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS 17 * ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE, 18 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT 20 * SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 23 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 24 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 25 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 26 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * $FreeBSD$ 30 */ 31 32 /* 33 * This is a simple program which demonstrates how to query the kernel 34 * routing mechanism using only a UDP socket. Pass it a hostname on 35 * the command line (sorry, it doesn't parse dotted decimal) and it will 36 * print out an IP address which names the interface over which UDP 37 * packets intended for that destination would be sent. 38 * A more sophisticated program might use the list obtained from SIOCGIFCONF 39 * to match the address with an interface name, but applications programmers 40 * much more often need to know the address of the interface rather than 41 * the name. 42 */ 43 #include <sys/types.h> 44 #include <sys/socket.h> 45 #include <unistd.h> 46 #include <netinet/in.h> 47 #include <arpa/inet.h> 48 #include <stdlib.h> 49 #include <stdio.h> 50 #include <netdb.h> 51 #include <err.h> 52 #include <errno.h> 53 #include <string.h> 54 #include <sysexits.h> 55 56 int 57 main(int argc, char **argv) 58 { 59 struct sockaddr_in local, remote; 60 struct hostent *hp; 61 int s, rv, namelen; 62 63 argc--, argv++; 64 65 if (!*argv) { 66 errx(EX_USAGE, "must supply a hostname"); 67 } 68 69 hp = gethostbyname(*argv); 70 if (!hp) { 71 errx(EX_NOHOST, "cannot resolve hostname: %s", *argv); 72 } 73 74 memcpy(&remote.sin_addr, hp->h_addr_list[0], sizeof remote.sin_addr); 75 remote.sin_port = htons(60000); 76 remote.sin_family = AF_INET; 77 remote.sin_len = sizeof remote; 78 79 local.sin_addr.s_addr = htonl(INADDR_ANY); 80 local.sin_port = htons(60000); 81 local.sin_family = AF_INET; 82 local.sin_len = sizeof local; 83 84 s = socket(PF_INET, SOCK_DGRAM, 0); 85 if (s < 0) 86 err(EX_OSERR, "socket"); 87 88 do { 89 rv = bind(s, (struct sockaddr *)&local, sizeof local); 90 local.sin_port = htons(ntohs(local.sin_port) + 1); 91 } while(rv < 0 && errno == EADDRINUSE); 92 93 if (rv < 0) 94 err(EX_OSERR, "bind"); 95 96 do { 97 rv = connect(s, (struct sockaddr *)&remote, sizeof remote); 98 remote.sin_port = htons(ntohs(remote.sin_port) + 1); 99 } while(rv < 0 && errno == EADDRINUSE); 100 101 if (rv < 0) 102 err(EX_OSERR, "connect"); 103 104 namelen = sizeof local; 105 rv = getsockname(s, (struct sockaddr *)&local, &namelen); 106 if (rv < 0) 107 err(EX_OSERR, "getsockname"); 108 109 printf("Route to %s is out %s\n", *argv, inet_ntoa(local.sin_addr)); 110 return 0; 111 } 112