arp.tproj/arp.c

   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 #ifndef lint
  38 static char const copyright[] =
  39 "@(#) Copyright (c) 1984, 1993\n\
  40         The Regents of the University of California.  All rights reserved.\n";
  41 #endif /* not lint */
  42
  43 #ifndef lint
  44 #if 0
  45 static char const sccsid[] = "@(#)from: arp.c   8.2 (Berkeley) 1/2/94";
  46 #endif
  47 static const char rcsid[] =
  48   "$FreeBSD: src/usr.sbin/arp/arp.c,v 1.22.2.10 2002/06/18 00:16:59 kbyanc Exp $";
  49 #endif /* not lint */
  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
  69 #include <netinet/in.h>
  70 #include <netinet/if_ether.h>
  71
  72 #include <arpa/inet.h>
  73
  74 #include <err.h>
  75 #include <errno.h>
  76 #include <netdb.h>
  77 #include <nlist.h>
  78 #include <paths.h>
  79 #include <stdio.h>
  80 #include <stdlib.h>
  81 #include <strings.h>
  82 #include <unistd.h>
  83
  84 #include <sys/types.h>
  85 #include <sys/socket.h>
  86 #include <net/ethernet.h>
  87
  88 void search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
  89         struct sockaddr_inarp *sin, struct rt_msghdr *rtm));
  90 void print_entry(struct sockaddr_dl *sdl,
  91         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  92 void nuke_entry(struct sockaddr_dl *sdl,
  93         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  94 int delete(char *host, char *info);
  95 void usage(void);
  96 int set(int argc, char **argv);
  97 int get(char *host);
  98 int file(char *name);
  99 void getsocket(void);
 100 int my_ether_aton(char *a, struct ether_addr *n);
 101 int rtmsg(int cmd);
 102 int get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr);
 103
 104 static int pid;
 105 static int nflag;       /* no reverse dns lookups */
 106 static int aflag;       /* do it for all entries */
 107 static int s = -1;
 108
 109 struct  sockaddr_in so_mask;
 110 struct  sockaddr_inarp blank_sin, sin_m;
 111 struct  sockaddr_dl blank_sdl, sdl_m;
 112 int     expire_time, flags, doing_proxy, proxy_only, found_entry;
 113 struct  {
 114         struct  rt_msghdr m_rtm;
 115         char    m_space[512];
 116 }       m_rtmsg;
 117
 118 /* which function we're supposed to do */
 119 #define F_GET           1
 120 #define F_SET           2
 121 #define F_FILESET       3
 122 #define F_REPLACE       4
 123 #define F_DELETE        5
 124
 125 #define ROUNDUP(a) \
 126         ((a) > 0 ? (1 + (((a) - 1) | (sizeof(long) - 1))) : sizeof(long))
 127 #define SETFUNC(f)      { if (func) usage(); func = (f); }
 128
 129 int
 130 main(int argc, char *argv[])
 131 {
 132         int ch, func = 0;
 133         int rtn = 0;
 134
 135         pid = getpid();
 136         while ((ch = getopt(argc, argv, "andfsS")) != -1)
 137                 switch((char)ch) {
 138                 case 'a':
 139                         aflag = 1;
 140                         break;
 141                 case 'd':
 142                         SETFUNC(F_DELETE);
 143                         break;
 144                 case 'n':
 145                         nflag = 1;
 146                         break;
 147                 case 'S':
 148                         SETFUNC(F_REPLACE);
 149                         break;
 150                 case 's':
 151                         SETFUNC(F_SET);
 152                         break;
 153                 case 'f' :
 154                         SETFUNC(F_FILESET);
 155                         break;
 156                 case '?':
 157                 default:
 158                         usage();
 159                 }
 160         argc -= optind;
 161         argv += optind;
 162
 163         bzero(&so_mask, sizeof(so_mask));
 164         so_mask.sin_len = 8;
 165         so_mask.sin_addr.s_addr = 0xffffffff;
 166         bzero(&blank_sin, sizeof(blank_sin));
 167         blank_sin.sin_len = sizeof(blank_sin);
 168         blank_sin.sin_family = AF_INET;
 169         bzero(&blank_sdl, sizeof(blank_sdl));
 170         blank_sdl.sdl_len = sizeof(blank_sdl);
 171         blank_sdl.sdl_family = AF_LINK;
 172
 173         if (!func)
 174                 func = F_GET;
 175         switch (func) {
 176         case F_GET:
 177                 if (aflag) {
 178                         if (argc != 0)
 179                                 usage();
 180                         search(0, print_entry);
 181                 } else {
 182                         if (argc != 1)
 183                                 usage();
 184                         get(argv[0]);
 185                 }
 186                 break;
 187         case F_SET:
 188         case F_REPLACE:
 189                 if (argc < 2 || argc > 6)
 190                         usage();
 191                 if (func == F_REPLACE)
 192                         (void) delete(argv[0], NULL);
 193                 rtn = set(argc, argv) ? 1 : 0;
 194                 break;
 195         case F_DELETE:
 196                 if (aflag) {
 197                         if (argc != 0)
 198                                 usage();
 199                         search(0, nuke_entry);
 200                 } else {
 201                         if (argc < 1 || argc > 2)
 202                                 usage();
 203                         rtn = delete(argv[0], argv[1]);
 204                 }
 205                 break;
 206         case F_FILESET:
 207                 if (argc != 1)
 208                         usage();
 209                 rtn = file(argv[0]);
 210                 break;
 211         }
 212
 213         return(rtn);
 214 }
 215
 216 /*
 217  * Process a file to set standard arp entries
 218  */
 219 int
 220 file(char *name)
 221 {
 222         FILE *fp;
 223         int i, retval;
 224         char line[100], arg[5][50], *args[5];
 225
 226         if ((fp = fopen(name, "r")) == NULL)
 227                 errx(1, "cannot open %s", name);
 228         args[0] = &arg[0][0];
 229         args[1] = &arg[1][0];
 230         args[2] = &arg[2][0];
 231         args[3] = &arg[3][0];
 232         args[4] = &arg[4][0];
 233         retval = 0;
 234         while(fgets(line, 100, fp) != NULL) {
 235                 i = sscanf(line, "%49s %49s %49s %49s %49s", arg[0], arg[1],
 236                     arg[2], arg[3], arg[4]);
 237                 if (i < 2) {
 238                         warnx("bad line: %s", line);
 239                         retval = 1;
 240                         continue;
 241                 }
 242                 if (set(i, args))
 243                         retval = 1;
 244         }
 245         fclose(fp);
 246         return (retval);
 247 }
 248
 249 void
 250 getsocket(void)
 251 {
 252         if (s < 0) {
 253                 s = socket(PF_ROUTE, SOCK_RAW, 0);
 254                 if (s < 0)
 255                         err(1, "socket");
 256         }
 257 }
 258
 259 /*
 260  * Set an individual arp entry
 261  */
 262 int
 263 set(int argc, char **argv)
 264 {
 265         struct hostent *hp;
 266         register struct sockaddr_inarp *addr = &sin_m;
 267         register struct sockaddr_dl *sdl;
 268         register struct rt_msghdr *rtm = &(m_rtmsg.m_rtm);
 269         struct ether_addr *ea;
 270         char *host = argv[0], *eaddr = argv[1];
 271
 272         getsocket();
 273         argc -= 2;
 274         argv += 2;
 275         sdl_m = blank_sdl;
 276         sin_m = blank_sin;
 277         addr->sin_addr.s_addr = inet_addr(host);
 278         if (addr->sin_addr.s_addr == INADDR_NONE) {
 279                 if (!(hp = gethostbyname(host))) {
 280                         warnx("%s: %s", host, hstrerror(h_errno));
 281                         return (1);
 282                 }
 283                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 284                     sizeof addr->sin_addr);
 285         }
 286         doing_proxy = flags = proxy_only = expire_time = 0;
 287         while (argc-- > 0) {
 288                 if (strncmp(argv[0], "temp", 4) == 0) {
 289                         struct timeval tv;
 290                         gettimeofday(&tv, 0);
 291                         expire_time = tv.tv_sec + 20 * 60;
 292                 }
 293                 else if (strncmp(argv[0], "pub", 3) == 0) {
 294                         flags |= RTF_ANNOUNCE;
 295                         doing_proxy = 1;
 296                         if (argc && strncmp(argv[1], "only", 3) == 0) {
 297                                 proxy_only = 1;
 298                                 sin_m.sin_other = SIN_PROXY;
 299                                 argc--; argv++;
 300                         }
 301                 } else if (strncmp(argv[0], "trail", 5) == 0) {
 302                         printf("%s: Sending trailers is no longer supported\n",
 303                                 host);
 304                 }
 305                 argv++;
 306         }
 307         ea = (struct ether_addr *)LLADDR(&sdl_m);
 308         if (doing_proxy && !strcmp(eaddr, "auto")) {
 309                 if (!get_ether_addr(addr->sin_addr.s_addr, ea)) {
 310                         printf("no interface found for %s\n",
 311                                inet_ntoa(addr->sin_addr));
 312                         return (1);
 313                 }
 314                 sdl_m.sdl_alen = ETHER_ADDR_LEN;
 315         } else {
 316                 if (my_ether_aton(eaddr, ea) == 0)
 317                         sdl_m.sdl_alen = ETHER_ADDR_LEN;
 318         }
 319 tryagain:
 320         if (rtmsg(RTM_GET) < 0) {
 321                 warn("%s", host);
 322                 return (1);
 323         }
 324         addr = (struct sockaddr_inarp *)(rtm + 1);
 325         sdl = (struct sockaddr_dl *)(ROUNDUP(addr->sin_len) + (char *)addr);
 326         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 327                 if (sdl->sdl_family == AF_LINK &&
 328                     (rtm->rtm_flags & RTF_LLINFO) &&
 329                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 330                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 331                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 332                         goto overwrite;
 333                 }
 334                 if (doing_proxy == 0) {
 335                         printf("set: can only proxy for %s\n", host);
 336                         return (1);
 337                 }
 338                 if (sin_m.sin_other & SIN_PROXY) {
 339                         printf("set: proxy entry exists for non 802 device\n");
 340                         return(1);
 341                 }
 342                 sin_m.sin_other = SIN_PROXY;
 343                 proxy_only = 1;
 344                 goto tryagain;
 345         }
 346 overwrite:
 347         if (sdl->sdl_family != AF_LINK) {
 348                 printf("cannot intuit interface index and type for %s\n", host);
 349                 return (1);
 350         }
 351         sdl_m.sdl_type = sdl->sdl_type;
 352         sdl_m.sdl_index = sdl->sdl_index;
 353         return (rtmsg(RTM_ADD));
 354 }
 355
 356 /*
 357  * Display an individual arp entry
 358  */
 359 int
 360 get(char *host)
 361 {
 362         struct hostent *hp;
 363         struct sockaddr_inarp *addr = &sin_m;
 364
 365         sin_m = blank_sin;
 366         addr->sin_addr.s_addr = inet_addr(host);
 367         if (addr->sin_addr.s_addr == INADDR_NONE) {
 368                 if (!(hp = gethostbyname(host)))
 369                         errx(1, "%s: %s", host, hstrerror(h_errno));
 370                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 371                     sizeof addr->sin_addr);
 372         }
 373         search(addr->sin_addr.s_addr, print_entry);
 374         if (found_entry == 0) {
 375                 printf("%s (%s) -- no entry\n",
 376                     host, inet_ntoa(addr->sin_addr));
 377                 return(1);
 378         }
 379         return(0);
 380 }
 381
 382 /*
 383  * Delete an arp entry
 384  */
 385 int
 386 delete(char *host, char *info)
 387 {
 388         struct hostent *hp;
 389         register struct sockaddr_inarp *addr = &sin_m;
 390         register struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 391         struct sockaddr_dl *sdl;
 392
 393         getsocket();
 394         sin_m = blank_sin;
 395         if (info) {
 396                 if (strncmp(info, "pub", 3) == 0)
 397                         sin_m.sin_other = SIN_PROXY;
 398                 else
 399                         usage();
 400         }
 401         addr->sin_addr.s_addr = inet_addr(host);
 402         if (addr->sin_addr.s_addr == INADDR_NONE) {
 403                 if (!(hp = gethostbyname(host))) {
 404                         warnx("%s: %s", host, hstrerror(h_errno));
 405                         return (1);
 406                 }
 407                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 408                     sizeof addr->sin_addr);
 409         }
 410 tryagain:
 411         if (rtmsg(RTM_GET) < 0) {
 412                 warn("%s", host);
 413                 return (1);
 414         }
 415         addr = (struct sockaddr_inarp *)(rtm + 1);
 416         sdl = (struct sockaddr_dl *)(ROUNDUP(addr->sin_len) + (char *)addr);
 417         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 418                 if (sdl->sdl_family == AF_LINK &&
 419                     (rtm->rtm_flags & RTF_LLINFO) &&
 420                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 421                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 422                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 423                         goto delete;
 424                 }
 425         }
 426         if (sin_m.sin_other & SIN_PROXY) {
 427                 fprintf(stderr, "delete: can't locate %s\n",host);
 428                 return (1);
 429         } else {
 430                 sin_m.sin_other = SIN_PROXY;
 431                 goto tryagain;
 432         }
 433 delete:
 434         if (sdl->sdl_family != AF_LINK) {
 435                 printf("cannot locate %s\n", host);
 436                 return (1);
 437         }
 438         if (rtmsg(RTM_DELETE) == 0) {
 439                 printf("%s (%s) deleted\n", host, inet_ntoa(addr->sin_addr));
 440                 return (0);
 441         }
 442         return (1);
 443 }
 444
 445 /*
 446  * Search the arp table and do some action on matching entries
 447  */
 448 void
 449 search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
 450         struct sockaddr_inarp *sin, struct rt_msghdr *rtm))
 451 {
 452         int mib[6];
 453         size_t needed;
 454         char *lim, *buf, *next;
 455         struct rt_msghdr *rtm;
 456         struct sockaddr_inarp *sin2;
 457         struct sockaddr_dl *sdl;
 458
 459         mib[0] = CTL_NET;
 460         mib[1] = PF_ROUTE;
 461         mib[2] = 0;
 462         mib[3] = AF_INET;
 463         mib[4] = NET_RT_FLAGS;
 464         mib[5] = RTF_LLINFO;
 465         if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
 466                 errx(1, "route-sysctl-estimate");
 467         if ((buf = malloc(needed)) == NULL)
 468                 errx(1, "malloc");
 469         if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0)
 470                 errx(1, "actual retrieval of routing table");
 471         lim = buf + needed;
 472         for (next = buf; next < lim; next += rtm->rtm_msglen) {
 473                 rtm = (struct rt_msghdr *)next;
 474                 sin2 = (struct sockaddr_inarp *)(rtm + 1);
 475                 sdl = (struct sockaddr_dl*)((char*)sin2 + ROUNDUP(sin2->sin_len));
 476                 if (addr) {
 477                         if (addr != sin2->sin_addr.s_addr)
 478                                 continue;
 479                         found_entry = 1;
 480                 }
 481                 (*action)(sdl, sin2, rtm);
 482         }
 483         free(buf);
 484 }
 485
 486
 487 /*
 488  * Stolen and adapted from ifconfig
 489  */
 490 static void
 491 print_lladdr(struct sockaddr_dl *sdl)
 492 {
 493         char *cp;
 494         int n;
 495
 496         cp = (char *)LLADDR(sdl);
 497         if ((n = sdl->sdl_alen) > 0) {
 498                 while (--n >= 0)
 499                         printf("%x%s",*cp++ & 0xff, n>0? ":" : "");
 500         }
 501 }
 502
 503
 504 /*
 505  * Display an arp entry
 506  */
 507 void
 508 print_entry(struct sockaddr_dl *sdl,
 509         struct sockaddr_inarp *addr, struct rt_msghdr *rtm)
 510 {
 511         const char *host;
 512         struct hostent *hp;
 513         char ifname[IF_NAMESIZE];
 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                 print_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 #ifndef __APPLE__
 552                 printf(" [token-ring]");
 553                 trld = SDL_ISO88025(sdl);
 554                 if (trld->trld_rcf != 0) {
 555                         printf(" rt=%x", ntohs(trld->trld_rcf));
 556                         for (seg = 0;
 557                              seg < ((TR_RCF_RIFLEN(trld->trld_rcf) - 2 ) / 2);
 558                              seg++)
 559                                 printf(":%x", ntohs(*(trld->trld_route[seg])));
 560                 }
 561 #endif
 562                 break;
 563             case IFT_L2VLAN:
 564                 printf(" [vlan]");
 565                 break;
 566             case IFT_IEEE1394:
 567                 printf(" [firewire]");
 568                 break;
 569             default:
 570                 break;
 571         }
 572
 573         printf("\n");
 574
 575 }
 576
 577 /*
 578  * Nuke an arp entry
 579  */
 580 void
 581 nuke_entry(struct sockaddr_dl *sdl,
 582         struct sockaddr_inarp *addr, struct rt_msghdr *rtm )
 583 {
 584         char ip[20];
 585
 586         snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
 587         delete(ip, NULL);
 588 }
 589
 590 int
 591 my_ether_aton(char *a, struct ether_addr *n)
 592 {
 593         struct ether_addr *ea;
 594
 595         if ((ea = ether_aton(a)) == NULL) {
 596                 warnx("invalid Ethernet address '%s'", a);
 597                 return (1);
 598         }
 599         *n = *ea;
 600         return (0);
 601 }
 602
 603 void
 604 usage(void)
 605 {
 606         fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
 607                 "usage: arp [-n] hostname",
 608                 "       arp [-n] -a",
 609                 "       arp -d hostname [pub]",
 610                 "       arp -d -a",
 611                 "       arp -s hostname ether_addr [temp] [pub]",
 612                 "       arp -S hostname ether_addr [temp] [pub]",
 613                 "       arp -f filename");
 614         exit(1);
 615 }
 616
 617 int
 618 rtmsg(int cmd)
 619 {
 620         static int seq;
 621         int rlen;
 622         register struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 623         register char *cp = m_rtmsg.m_space;
 624         register int l;
 625
 626         errno = 0;
 627         if (cmd == RTM_DELETE)
 628                 goto doit;
 629         bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
 630         rtm->rtm_flags = flags;
 631         rtm->rtm_version = RTM_VERSION;
 632
 633         switch (cmd) {
 634         default:
 635                 errx(1, "internal wrong cmd");
 636         case RTM_ADD:
 637                 rtm->rtm_addrs |= RTA_GATEWAY;
 638                 rtm->rtm_rmx.rmx_expire = expire_time;
 639                 rtm->rtm_inits = RTV_EXPIRE;
 640                 rtm->rtm_flags |= (RTF_HOST | RTF_STATIC);
 641                 sin_m.sin_other = 0;
 642                 if (doing_proxy) {
 643                         if (proxy_only)
 644                                 sin_m.sin_other = SIN_PROXY;
 645                         else {
 646                                 rtm->rtm_addrs |= RTA_NETMASK;
 647                                 rtm->rtm_flags &= ~RTF_HOST;
 648                         }
 649                 }
 650                 /* FALLTHROUGH */
 651         case RTM_GET:
 652                 rtm->rtm_addrs |= RTA_DST;
 653         }
 654 #define NEXTADDR(w, s) \
 655         if (rtm->rtm_addrs & (w)) { \
 656                 bcopy((char *)&s, cp, sizeof(s)); cp += ROUNDUP(sizeof(s));}
 657
 658         NEXTADDR(RTA_DST, sin_m);
 659         NEXTADDR(RTA_GATEWAY, sdl_m);
 660         NEXTADDR(RTA_NETMASK, so_mask);
 661
 662         rtm->rtm_msglen = cp - (char *)&m_rtmsg;
 663 doit:
 664         l = rtm->rtm_msglen;
 665         rtm->rtm_seq = ++seq;
 666         rtm->rtm_type = cmd;
 667         if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
 668                 if (errno != ESRCH || cmd != RTM_DELETE) {
 669                         warn("writing to routing socket");
 670                         return (-1);
 671                 }
 672         }
 673         do {
 674                 l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
 675         } while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
 676         if (l < 0)
 677                 warn("read from routing socket");
 678         return (0);
 679 }
 680
 681 /*
 682  * get_ether_addr - get the hardware address of an interface on the
 683  * the same subnet as ipaddr.
 684  */
 685 #define MAX_IFS         32
 686
 687 int
 688 get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr)
 689 {
 690         struct ifreq *ifr, *ifend, *ifp;
 691         u_int32_t ina, mask;
 692         struct sockaddr_dl *dla;
 693         struct ifreq ifreq;
 694         struct ifconf ifc;
 695         struct ifreq ifs[MAX_IFS];
 696         int sock;
 697
 698         sock = socket(AF_INET, SOCK_DGRAM, 0);
 699         if (sock < 0)
 700                 err(1, "socket");
 701
 702         ifc.ifc_len = sizeof(ifs);
 703         ifc.ifc_req = ifs;
 704         if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
 705                 warnx("ioctl(SIOCGIFCONF)");
 706                 close(sock);
 707                 return 0;
 708         }
 709
 710         /*
 711         * Scan through looking for an interface with an Internet
 712         * address on the same subnet as `ipaddr'.
 713         */
 714         ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
 715         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 716                 if (ifr->ifr_addr.sa_family == AF_INET) {
 717                         ina = ((struct sockaddr_in *)
 718                                 &ifr->ifr_addr)->sin_addr.s_addr;
 719                         strncpy(ifreq.ifr_name, ifr->ifr_name,
 720                                 sizeof(ifreq.ifr_name));
 721                         /*
 722                          * Check that the interface is up,
 723                          * and not point-to-point or loopback.
 724                          */
 725                         if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
 726                                 continue;
 727                         if ((ifreq.ifr_flags &
 728                              (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
 729                                         IFF_LOOPBACK|IFF_NOARP))
 730                              != (IFF_UP|IFF_BROADCAST))
 731                                 goto nextif;
 732                         /*
 733                          * Get its netmask and check that it's on
 734                          * the right subnet.
 735                          */
 736                         if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
 737                                 continue;
 738                         mask = ((struct sockaddr_in *)
 739                                 &ifreq.ifr_addr)->sin_addr.s_addr;
 740                         if ((ipaddr & mask) != (ina & mask))
 741                                 goto nextif;
 742                         break;
 743                 }
 744 nextif:
 745                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 746                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 747         }
 748
 749         if (ifr >= ifend) {
 750                 close(sock);
 751                 return 0;
 752         }
 753
 754         /*
 755         * Now scan through again looking for a link-level address
 756         * for this interface.
 757         */
 758         ifp = ifr;
 759         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 760                 if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0
 761                     && ifr->ifr_addr.sa_family == AF_LINK) {
 762                         /*
 763                          * Found the link-level address - copy it out
 764                          */
 765                         dla = (struct sockaddr_dl *) &ifr->ifr_addr;
 766                         close (sock);
 767                         printf("using interface %s for proxy with address ",
 768                                 ifp->ifr_name);
 769                         print_lladdr(dla);
 770                         printf("\n");
 771                         return dla->sdl_alen;
 772                 }
 773                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 774                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 775         }
 776         return 0;
 777 }