arp.c revision 128181
1/* 2 * Copyright (c) 1984, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Sun Microsystems, Inc. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 */ 36 37#if 0 38#ifndef lint 39static char const copyright[] = 40"@(#) Copyright (c) 1984, 1993\n\ 41 The Regents of the University of California. All rights reserved.\n"; 42#endif /* not lint */ 43 44#ifndef lint 45static char const sccsid[] = "@(#)from: arp.c 8.2 (Berkeley) 1/2/94"; 46#endif /* not lint */ 47#endif 48#include <sys/cdefs.h> 49__FBSDID("$FreeBSD: head/usr.sbin/arp/arp.c 128181 2004-04-13 08:34:52Z luigi $"); 50 51/* 52 * arp - display, set, and delete arp table entries 53 */ 54 55 56#include <sys/param.h> 57#include <sys/file.h> 58#include <sys/socket.h> 59#include <sys/sockio.h> 60#include <sys/sysctl.h> 61#include <sys/ioctl.h> 62#include <sys/time.h> 63 64#include <net/if.h> 65#include <net/if_dl.h> 66#include <net/if_types.h> 67#include <net/route.h> 68#include <net/iso88025.h> 69 70#include <netinet/in.h> 71#include <netinet/if_ether.h> 72 73#include <arpa/inet.h> 74 75#include <ctype.h> 76#include <err.h> 77#include <errno.h> 78#include <netdb.h> 79#include <nlist.h> 80#include <paths.h> 81#include <stdio.h> 82#include <stdlib.h> 83#include <string.h> 84#include <strings.h> 85#include <unistd.h> 86 87typedef void (action_fn)(struct sockaddr_dl *sdl, 88 struct sockaddr_inarp *s_in, struct rt_msghdr *rtm); 89 90static int search(u_long addr, action_fn *action); 91static action_fn print_entry; 92static action_fn nuke_entry; 93 94static int delete(char *host, char *info); 95static void usage(void); 96static int set(int argc, char **argv); 97static int get(char *host); 98static int file(char *name); 99static int my_ether_aton(char *a, struct ether_addr *n); 100static struct rt_msghdr *rtmsg(int cmd); 101static int get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr); 102 103static int nflag; /* no reverse dns lookups */ 104static char *rifname; 105 106static struct sockaddr_inarp blank_sin, sin_m; 107static struct sockaddr_dl sdl_m; 108static int expire_time, flags, doing_proxy, proxy_only; 109/* which function we're supposed to do */ 110#define F_GET 1 111#define F_SET 2 112#define F_FILESET 3 113#define F_REPLACE 4 114#define F_DELETE 5 115 116#define ROUNDUP(a) \ 117 ((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long)) 118#define SETFUNC(f) { if (func) usage(); func = (f); } 119 120int 121main(int argc, char *argv[]) 122{ 123 int ch, func = 0; 124 int rtn = 0; 125 int aflag = 0; /* do it for all entries */ 126 127 while ((ch = getopt(argc, argv, "andfsSi:")) != -1) 128 switch((char)ch) { 129 case 'a': 130 aflag = 1; 131 break; 132 case 'd': 133 SETFUNC(F_DELETE); 134 break; 135 case 'n': 136 nflag = 1; 137 break; 138 case 'S': 139 SETFUNC(F_REPLACE); 140 break; 141 case 's': 142 SETFUNC(F_SET); 143 break; 144 case 'f' : 145 SETFUNC(F_FILESET); 146 break; 147 case 'i': 148 rifname = optarg; 149 break; 150 case '?': 151 default: 152 usage(); 153 } 154 argc -= optind; 155 argv += optind; 156 157 bzero(&blank_sin, sizeof(blank_sin)); 158 blank_sin.sin_len = sizeof(blank_sin); 159 blank_sin.sin_family = AF_INET; 160 161 if (!func) 162 func = F_GET; 163 if (rifname) { 164 if (func != F_GET) 165 errx(1, "-i not applicable to this operation"); 166 if (if_nametoindex(rifname) == 0) { 167 if (errno == ENXIO) 168 errx(1, "interface %s does not exist", rifname); 169 else 170 err(1, "if_nametoindex(%s)", rifname); 171 } 172 } 173 switch (func) { 174 case F_GET: 175 if (aflag) { 176 if (argc != 0) 177 usage(); 178 search(0, print_entry); 179 } else { 180 if (argc != 1) 181 usage(); 182 get(argv[0]); 183 } 184 break; 185 case F_SET: 186 case F_REPLACE: 187 if (argc < 2 || argc > 6) 188 usage(); 189 if (func == F_REPLACE) 190 (void) delete(argv[0], NULL); 191 rtn = set(argc, argv) ? 1 : 0; 192 break; 193 case F_DELETE: 194 if (aflag) { 195 if (argc != 0) 196 usage(); 197 search(0, nuke_entry); 198 } else { 199 if (argc < 1 || argc > 2) 200 usage(); 201 rtn = delete(argv[0], argv[1]); 202 } 203 break; 204 case F_FILESET: 205 if (argc != 1) 206 usage(); 207 rtn = file(argv[0]); 208 break; 209 } 210 211 return(rtn); 212} 213 214/* 215 * Process a file to set standard arp entries 216 */ 217static int 218file(char *name) 219{ 220 FILE *fp; 221 int i, retval; 222 char line[100], arg[5][50], *args[5], *p; 223 224 if ((fp = fopen(name, "r")) == NULL) 225 err(1, "cannot open %s", name); 226 args[0] = &arg[0][0]; 227 args[1] = &arg[1][0]; 228 args[2] = &arg[2][0]; 229 args[3] = &arg[3][0]; 230 args[4] = &arg[4][0]; 231 retval = 0; 232 while(fgets(line, 100, fp) != NULL) { 233 if ((p = strchr(line, '#')) != NULL) 234 *p = '\0'; 235 for (p = line; isblank(*p); p++); 236 if (*p == '\n' || *p == '\0') 237 continue; 238 i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1], 239 arg[2], arg[3], arg[4]); 240 if (i < 2) { 241 warnx("bad line: %s", line); 242 retval = 1; 243 continue; 244 } 245 if (set(i, args)) 246 retval = 1; 247 } 248 fclose(fp); 249 return (retval); 250} 251 252/* 253 * Set an individual arp entry 254 */ 255int 256set(int argc, char **argv) 257{ 258 struct hostent *hp; 259 struct sockaddr_inarp *addr = &sin_m; 260 struct sockaddr_dl *sdl; 261 struct rt_msghdr *rtm; 262 struct ether_addr *ea; 263 char *host = argv[0], *eaddr = argv[1]; 264 265 argc -= 2; 266 argv += 2; 267 268 bzero(&sdl_m, sizeof(sdl_m)); 269 sdl_m.sdl_len = sizeof(sdl_m); 270 sdl_m.sdl_family = AF_LINK; 271 272 sin_m = blank_sin; 273 addr->sin_addr.s_addr = inet_addr(host); 274 if (addr->sin_addr.s_addr == INADDR_NONE) { 275 if (!(hp = gethostbyname(host))) { 276 warnx("%s: %s", host, hstrerror(h_errno)); 277 return (1); 278 } 279 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr, 280 sizeof addr->sin_addr); 281 } 282 doing_proxy = flags = proxy_only = expire_time = 0; 283 while (argc-- > 0) { 284 if (strncmp(argv[0], "temp", 4) == 0) { 285 struct timeval tv; 286 gettimeofday(&tv, 0); 287 expire_time = tv.tv_sec + 20 * 60; 288 } 289 else if (strncmp(argv[0], "pub", 3) == 0) { 290 flags |= RTF_ANNOUNCE; 291 doing_proxy = 1; 292 if (argc && strncmp(argv[1], "only", 3) == 0) { 293 proxy_only = 1; 294 sin_m.sin_other = SIN_PROXY; 295 argc--; argv++; 296 } 297 } else if (strncmp(argv[0], "trail", 5) == 0) { 298 printf("%s: Sending trailers is no longer supported\n", 299 host); 300 } 301 argv++; 302 } 303 ea = (struct ether_addr *)LLADDR(&sdl_m); 304 if (doing_proxy && !strcmp(eaddr, "auto")) { 305 if (!get_ether_addr(addr->sin_addr.s_addr, ea)) { 306 printf("no interface found for %s\n", 307 inet_ntoa(addr->sin_addr)); 308 return (1); 309 } 310 sdl_m.sdl_alen = ETHER_ADDR_LEN; 311 } else { 312 if (my_ether_aton(eaddr, ea) == 0) 313 sdl_m.sdl_alen = ETHER_ADDR_LEN; 314 } 315tryagain: 316 rtm = rtmsg(RTM_GET); 317 if (rtm == NULL) { 318 warn("%s", host); 319 return (1); 320 } 321 addr = (struct sockaddr_inarp *)(rtm + 1); 322 sdl = (struct sockaddr_dl *)(ROUNDUP(addr->sin_len) + (char *)addr); 323 if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) { 324 if (sdl->sdl_family == AF_LINK && 325 (rtm->rtm_flags & RTF_LLINFO) && 326 !(rtm->rtm_flags & RTF_GATEWAY)) 327 switch (sdl->sdl_type) { 328 case IFT_ETHER: 329 case IFT_FDDI: 330 case IFT_ISO88023: 331 case IFT_ISO88024: 332 case IFT_ISO88025: 333 case IFT_L2VLAN: 334 goto overwrite; 335 } 336 if (doing_proxy == 0) { 337 printf("set: can only proxy for %s\n", host); 338 return (1); 339 } 340 if (sin_m.sin_other & SIN_PROXY) { 341 printf("set: proxy entry exists for non 802 device\n"); 342 return(1); 343 } 344 sin_m.sin_other = SIN_PROXY; 345 proxy_only = 1; 346 goto tryagain; 347 } 348overwrite: 349 if (sdl->sdl_family != AF_LINK) { 350 printf("cannot intuit interface index and type for %s\n", host); 351 return (1); 352 } 353 sdl_m.sdl_type = sdl->sdl_type; 354 sdl_m.sdl_index = sdl->sdl_index; 355 return (rtmsg(RTM_ADD) != NULL); 356} 357 358/* 359 * Display an individual arp entry 360 */ 361static int 362get(char *host) 363{ 364 struct hostent *hp; 365 struct sockaddr_inarp *addr = &sin_m; 366 367 sin_m = blank_sin; 368 addr->sin_addr.s_addr = inet_addr(host); 369 if (addr->sin_addr.s_addr == INADDR_NONE) { 370 if (!(hp = gethostbyname(host))) 371 errx(1, "%s: %s", host, hstrerror(h_errno)); 372 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr, 373 sizeof addr->sin_addr); 374 } 375 if (0 == search(addr->sin_addr.s_addr, print_entry)) { 376 printf("%s (%s) -- no entry", 377 host, inet_ntoa(addr->sin_addr)); 378 if (rifname) 379 printf(" on %s", rifname); 380 printf("\n"); 381 return(1); 382 } 383 return(0); 384} 385 386/* 387 * Delete an arp entry 388 */ 389static int 390delete(char *host, char *info) 391{ 392 struct hostent *hp; 393 struct sockaddr_inarp *addr = &sin_m; 394 struct rt_msghdr *rtm; 395 struct sockaddr_dl *sdl; 396 397 sin_m = blank_sin; 398 if (info) { 399 if (strncmp(info, "pub", 3) == 0) 400 sin_m.sin_other = SIN_PROXY; 401 else 402 usage(); 403 } 404 addr->sin_addr.s_addr = inet_addr(host); 405 if (addr->sin_addr.s_addr == INADDR_NONE) { 406 if (!(hp = gethostbyname(host))) { 407 warnx("%s: %s", host, hstrerror(h_errno)); 408 return (1); 409 } 410 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr, 411 sizeof addr->sin_addr); 412 } 413tryagain: 414 rtm = rtmsg(RTM_GET); 415 if (rtm == NULL) { 416 warn("%s", host); 417 return (1); 418 } 419 addr = (struct sockaddr_inarp *)(rtm + 1); 420 sdl = (struct sockaddr_dl *)(ROUNDUP(addr->sin_len) + (char *)addr); 421 if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) { 422 if (sdl->sdl_family == AF_LINK && 423 (rtm->rtm_flags & RTF_LLINFO) && 424 !(rtm->rtm_flags & RTF_GATEWAY)) 425 switch (sdl->sdl_type) { 426 case IFT_ETHER: 427 case IFT_FDDI: 428 case IFT_ISO88023: 429 case IFT_ISO88024: 430 case IFT_ISO88025: 431 case IFT_L2VLAN: 432 goto delete; 433 } 434 } 435 if (sin_m.sin_other & SIN_PROXY) { 436 fprintf(stderr, "delete: can't locate %s\n",host); 437 return (1); 438 } else { 439 sin_m.sin_other = SIN_PROXY; 440 goto tryagain; 441 } 442delete: 443 if (sdl->sdl_family != AF_LINK) { 444 printf("cannot locate %s\n", host); 445 return (1); 446 } 447 if (rtmsg(RTM_DELETE) != NULL) { 448 printf("%s (%s) deleted\n", host, inet_ntoa(addr->sin_addr)); 449 return (0); 450 } 451 return (1); 452} 453 454/* 455 * Search the arp table and do some action on matching entries 456 */ 457static int 458search(u_long addr, action_fn *action) 459{ 460 int mib[6]; 461 size_t needed; 462 char *lim, *buf, *next; 463 struct rt_msghdr *rtm; 464 struct sockaddr_inarp *sin2; 465 struct sockaddr_dl *sdl; 466 char ifname[IF_NAMESIZE]; 467 int found_entry = 0; 468 469 mib[0] = CTL_NET; 470 mib[1] = PF_ROUTE; 471 mib[2] = 0; 472 mib[3] = AF_INET; 473 mib[4] = NET_RT_FLAGS; 474 mib[5] = RTF_LLINFO; 475 if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0) 476 err(1, "route-sysctl-estimate"); 477 if (needed == 0) 478 return 0; 479 if ((buf = malloc(needed)) == NULL) 480 err(1, "malloc"); 481 if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0) 482 err(1, "actual retrieval of routing table"); 483 lim = buf + needed; 484 for (next = buf; next < lim; next += rtm->rtm_msglen) { 485 rtm = (struct rt_msghdr *)next; 486 sin2 = (struct sockaddr_inarp *)(rtm + 1); 487 (char *)sdl = (char *)sin2 + ROUNDUP(sin2->sin_len); 488 if (rifname && if_indextoname(sdl->sdl_index, ifname) && 489 strcmp(ifname, rifname)) 490 continue; 491 if (addr) { 492 if (addr != sin2->sin_addr.s_addr) 493 continue; 494 found_entry = 1; 495 } 496 (*action)(sdl, sin2, rtm); 497 } 498 free(buf); 499 return found_entry; 500} 501 502/* 503 * Display an arp entry 504 */ 505static void 506print_entry(struct sockaddr_dl *sdl, 507 struct sockaddr_inarp *addr, struct rt_msghdr *rtm) 508{ 509 const char *host; 510 struct hostent *hp; 511 struct iso88025_sockaddr_dl_data *trld; 512 char ifname[IF_NAMESIZE]; 513 int seg; 514 515 if (nflag == 0) 516 hp = gethostbyaddr((caddr_t)&(addr->sin_addr), 517 sizeof addr->sin_addr, AF_INET); 518 else 519 hp = 0; 520 if (hp) 521 host = hp->h_name; 522 else { 523 host = "?"; 524 if (h_errno == TRY_AGAIN) 525 nflag = 1; 526 } 527 printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr)); 528 if (sdl->sdl_alen) 529 printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl))); 530 else 531 printf("(incomplete)"); 532 if (if_indextoname(sdl->sdl_index, ifname) != NULL) 533 printf(" on %s", ifname); 534 if (rtm->rtm_rmx.rmx_expire == 0) 535 printf(" permanent"); 536 if (addr->sin_other & SIN_PROXY) 537 printf(" published (proxy only)"); 538 if (rtm->rtm_addrs & RTA_NETMASK) { 539 addr = (struct sockaddr_inarp *) 540 (ROUNDUP(sdl->sdl_len) + (char *)sdl); 541 if (addr->sin_addr.s_addr == 0xffffffff) 542 printf(" published"); 543 if (addr->sin_len != 8) 544 printf("(weird)"); 545 } 546 switch(sdl->sdl_type) { 547 case IFT_ETHER: 548 printf(" [ethernet]"); 549 break; 550 case IFT_ISO88025: 551 printf(" [token-ring]"); 552 trld = SDL_ISO88025(sdl); 553 if (trld->trld_rcf != 0) { 554 printf(" rt=%x", ntohs(trld->trld_rcf)); 555 for (seg = 0; 556 seg < ((TR_RCF_RIFLEN(trld->trld_rcf) - 2 ) / 2); 557 seg++) 558 printf(":%x", ntohs(*(trld->trld_route[seg]))); 559 } 560 break; 561 case IFT_FDDI: 562 printf(" [fddi]"); 563 break; 564 case IFT_ATM: 565 printf(" [atm]"); 566 break; 567 case IFT_L2VLAN: 568 printf(" [vlan]"); 569 break; 570 default: 571 break; 572 } 573 574 printf("\n"); 575 576} 577 578/* 579 * Nuke an arp entry 580 */ 581static void 582nuke_entry(struct sockaddr_dl *sdl __unused, 583 struct sockaddr_inarp *addr, struct rt_msghdr *rtm __unused) 584{ 585 char ip[20]; 586 587 snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr)); 588 delete(ip, NULL); 589} 590 591static int 592my_ether_aton(char *a, struct ether_addr *n) 593{ 594 struct ether_addr *ea; 595 596 if ((ea = ether_aton(a)) == NULL) { 597 warnx("invalid Ethernet address '%s'", a); 598 return (1); 599 } 600 *n = *ea; 601 return (0); 602} 603 604static void 605usage(void) 606{ 607 fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n", 608 "usage: arp [-n] [-i interface] hostname", 609 " arp [-n] [-i interface] -a", 610 " arp -d hostname [pub]", 611 " arp -d -a", 612 " arp -s hostname ether_addr [temp] [pub]", 613 " arp -S hostname ether_addr [temp] [pub]", 614 " arp -f filename"); 615 exit(1); 616} 617 618static struct rt_msghdr * 619rtmsg(int cmd) 620{ 621 static int seq; 622 int rlen; 623 int l; 624 struct sockaddr_in so_mask; 625 static int s = -1; 626 static pid_t pid; 627 628 static struct { 629 struct rt_msghdr m_rtm; 630 char m_space[512]; 631 } m_rtmsg; 632 633 struct rt_msghdr *rtm = &m_rtmsg.m_rtm; 634 char *cp = m_rtmsg.m_space; 635 636 if (s < 0) { /* first time: open socket, get pid */ 637 s = socket(PF_ROUTE, SOCK_RAW, 0); 638 if (s < 0) 639 err(1, "socket"); 640 pid = getpid(); 641 } 642 bzero(&so_mask, sizeof(so_mask)); 643 so_mask.sin_len = 8; 644 so_mask.sin_addr.s_addr = 0xffffffff; 645 646 errno = 0; 647 if (cmd == RTM_DELETE) 648 goto doit; 649 bzero((char *)&m_rtmsg, sizeof(m_rtmsg)); 650 rtm->rtm_flags = flags; 651 rtm->rtm_version = RTM_VERSION; 652 653 switch (cmd) { 654 default: 655 errx(1, "internal wrong cmd"); 656 case RTM_ADD: 657 rtm->rtm_addrs |= RTA_GATEWAY; 658 rtm->rtm_rmx.rmx_expire = expire_time; 659 rtm->rtm_inits = RTV_EXPIRE; 660 rtm->rtm_flags |= (RTF_HOST | RTF_STATIC); 661 sin_m.sin_other = 0; 662 if (doing_proxy) { 663 if (proxy_only) 664 sin_m.sin_other = SIN_PROXY; 665 else { 666 rtm->rtm_addrs |= RTA_NETMASK; 667 rtm->rtm_flags &= ~RTF_HOST; 668 } 669 } 670 /* FALLTHROUGH */ 671 case RTM_GET: 672 rtm->rtm_addrs |= RTA_DST; 673 } 674#define NEXTADDR(w, s) \ 675 if (rtm->rtm_addrs & (w)) { \ 676 bcopy((char *)&s, cp, sizeof(s)); cp += ROUNDUP(sizeof(s));} 677 678 NEXTADDR(RTA_DST, sin_m); 679 NEXTADDR(RTA_GATEWAY, sdl_m); 680 NEXTADDR(RTA_NETMASK, so_mask); 681 682 rtm->rtm_msglen = cp - (char *)&m_rtmsg; 683doit: 684 l = rtm->rtm_msglen; 685 rtm->rtm_seq = ++seq; 686 rtm->rtm_type = cmd; 687 if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) { 688 if (errno != ESRCH || cmd != RTM_DELETE) { 689 warn("writing to routing socket"); 690 return NULL; 691 } 692 } 693 do { 694 l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg)); 695 } while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid)); 696 if (l < 0) 697 warn("read from routing socket"); 698 return rtm; 699} 700 701/* 702 * get_ether_addr - get the hardware address of an interface on the 703 * the same subnet as ipaddr. 704 */ 705#define MAX_IFS 32 706 707static int 708get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr) 709{ 710 struct ifreq *ifr, *ifend, *ifp; 711 u_int32_t ina, mask; 712 struct sockaddr_dl *dla; 713 struct ifreq ifreq; 714 struct ifconf ifc; 715 struct ifreq ifs[MAX_IFS]; 716 int sock; 717 718 sock = socket(AF_INET, SOCK_DGRAM, 0); 719 if (sock < 0) 720 err(1, "socket"); 721 722 ifc.ifc_len = sizeof(ifs); 723 ifc.ifc_req = ifs; 724 if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) { 725 warnx("ioctl(SIOCGIFCONF)"); 726 close(sock); 727 return 0; 728 } 729 730 /* 731 * Scan through looking for an interface with an Internet 732 * address on the same subnet as `ipaddr'. 733 */ 734 ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len); 735 for (ifr = ifc.ifc_req; ifr < ifend; ) { 736 if (ifr->ifr_addr.sa_family == AF_INET) { 737 ina = ((struct sockaddr_in *) 738 &ifr->ifr_addr)->sin_addr.s_addr; 739 strncpy(ifreq.ifr_name, ifr->ifr_name, 740 sizeof(ifreq.ifr_name)); 741 /* 742 * Check that the interface is up, 743 * and not point-to-point or loopback. 744 */ 745 if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0) 746 continue; 747 if ((ifreq.ifr_flags & 748 (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT| 749 IFF_LOOPBACK|IFF_NOARP)) 750 != (IFF_UP|IFF_BROADCAST)) 751 goto nextif; 752 /* 753 * Get its netmask and check that it's on 754 * the right subnet. 755 */ 756 if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0) 757 continue; 758 mask = ((struct sockaddr_in *) 759 &ifreq.ifr_addr)->sin_addr.s_addr; 760 if ((ipaddr & mask) != (ina & mask)) 761 goto nextif; 762 break; 763 } 764nextif: 765 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr 766 + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr))); 767 } 768 769 if (ifr >= ifend) { 770 close(sock); 771 return 0; 772 } 773 774 /* 775 * Now scan through again looking for a link-level address 776 * for this interface. 777 */ 778 ifp = ifr; 779 for (ifr = ifc.ifc_req; ifr < ifend; ) { 780 if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0 781 && ifr->ifr_addr.sa_family == AF_LINK) { 782 /* 783 * Found the link-level address - copy it out 784 */ 785 dla = (struct sockaddr_dl *) &ifr->ifr_addr; 786 memcpy(hwaddr, LLADDR(dla), dla->sdl_alen); 787 close (sock); 788 printf("using interface %s for proxy with address ", 789 ifp->ifr_name); 790 printf("%s\n", ether_ntoa(hwaddr)); 791 return dla->sdl_alen; 792 } 793 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr 794 + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr))); 795 } 796 return 0; 797} 798