usr.sbin/arp/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. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  * @(#)from: arp.c      8.2 (Berkeley) 1/2/94
  33  * $FreeBSD: src/usr.sbin/arp/arp.c,v 1.22.2.12 2003/04/16 10:02:37 ru Exp $
  34  */
  35
  36 /*
  37  * arp - display, set, and delete arp table entries
  38  */
  39
  40
  41 #include <sys/param.h>
  42 #include <sys/file.h>
  43 #include <sys/socket.h>
  44 #include <sys/sockio.h>
  45 #include <sys/sysctl.h>
  46 #include <sys/ioctl.h>
  47 #include <sys/time.h>
  48
  49 #include <net/if.h>
  50 #include <net/if_dl.h>
  51 #include <net/if_types.h>
  52 #include <net/route.h>
  53
  54 #include <netinet/in.h>
  55 #include <netinet/if_ether.h>
  56
  57 #include <arpa/inet.h>
  58
  59 #include <ctype.h>
  60 #include <err.h>
  61 #include <errno.h>
  62 #include <netdb.h>
  63 #include <nlist.h>
  64 #include <paths.h>
  65 #include <stdio.h>
  66 #include <stdlib.h>
  67 #include <string.h>
  68 #include <unistd.h>
  69
  70 static void search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
  71         struct sockaddr_inarp *sin, struct rt_msghdr *rtm));
  72 static void print_entry(struct sockaddr_dl *sdl,
  73         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  74 static void nuke_entry(struct sockaddr_dl *sdl,
  75         struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
  76 static int delete(char *host, char *info);
  77 static void usage(void) __dead2;
  78 static int set(int argc, char **argv);
  79 static int get(char *host);
  80 static int file(char *name);
  81 static void getsocket(void);
  82 static int my_ether_aton(char *a, struct ether_addr *n);
  83 static int rtmsg(int cmd);
  84 static int get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr);
  85
  86 static int pid;
  87 static int nflag;       /* no reverse dns lookups */
  88 static int aflag;       /* do it for all entries */
  89 static int cpuflag = -1;
  90 static int s = -1;
  91 static int rifindex = 0;
  92 static const char *rifname = NULL;
  93
  94 static struct   sockaddr_in so_mask;
  95 static struct   sockaddr_inarp blank_sin, sin_m;
  96 static struct   sockaddr_dl blank_sdl, sdl_m;
  97 static int      flags, doing_proxy, proxy_only, found_entry;
  98 static time_t   expire_time;
  99 static struct   {
 100         struct  rt_msghdr m_rtm;
 101         char    m_space[512];
 102 }       m_rtmsg;
 103
 104 /* which function we're supposed to do */
 105 #define F_GET           1
 106 #define F_SET           2
 107 #define F_FILESET       3
 108 #define F_REPLACE       4
 109 #define F_DELETE        5
 110
 111 #define SETFUNC(f)      { if (func) usage(); func = (f); }
 112
 113 int
 114 main(int argc, char **argv)
 115 {
 116         int ch, func = 0;
 117         int rtn = 0;
 118
 119         pid = getpid();
 120         while ((ch = getopt(argc, argv, "ac:i:ndfsS")) != -1)
 121                 switch((char)ch) {
 122                 case 'a':
 123                         aflag = 1;
 124                         break;
 125                 case 'c':
 126                         cpuflag = strtol(optarg, NULL, 0);
 127                         break;
 128                 case 'i':
 129                         rifname = optarg;
 130                         break;
 131                 case 'd':
 132                         SETFUNC(F_DELETE);
 133                         break;
 134                 case 'n':
 135                         nflag = 1;
 136                         break;
 137                 case 'S':
 138                         SETFUNC(F_REPLACE);
 139                         break;
 140                 case 's':
 141                         SETFUNC(F_SET);
 142                         break;
 143                 case 'f' :
 144                         SETFUNC(F_FILESET);
 145                         break;
 146                 case '?':
 147                 default:
 148                         usage();
 149                 }
 150         argc -= optind;
 151         argv += optind;
 152
 153         bzero(&so_mask, sizeof(so_mask));
 154         so_mask.sin_len = 8;
 155         so_mask.sin_addr.s_addr = 0xffffffff;
 156         bzero(&blank_sin, sizeof(blank_sin));
 157         blank_sin.sin_len = sizeof(blank_sin);
 158         blank_sin.sin_family = AF_INET;
 159         bzero(&blank_sdl, sizeof(blank_sdl));
 160         blank_sdl.sdl_len = sizeof(blank_sdl);
 161         blank_sdl.sdl_family = AF_LINK;
 162
 163         if (func == 0)
 164                 func = F_GET;
 165         if (rifname != NULL) {
 166                 if (func != F_GET && !(func == F_DELETE && aflag))
 167                         errx(1, "-i not applicable to this operation");
 168                 if ((rifindex = if_nametoindex(rifname)) == 0) {
 169                         if (errno == ENXIO)
 170                                 errx(1, "interface %s does not exist",
 171                                      rifname);
 172                         else
 173                                 err(1, "if_nametoindex(%s)", rifname);
 174                 }
 175         }
 176
 177         switch (func) {
 178         case F_GET:
 179                 if (aflag) {
 180                         if (argc != 0)
 181                                 usage();
 182                         search(0, print_entry);
 183                 } else {
 184                         if (argc != 1)
 185                                 usage();
 186                         get(argv[0]);
 187                 }
 188                 break;
 189         case F_SET:
 190         case F_REPLACE:
 191                 if (argc < 2 || argc > 6)
 192                         usage();
 193                 if (func == F_REPLACE)
 194                         delete(argv[0], NULL);
 195                 rtn = set(argc, argv) ? 1 : 0;
 196                 break;
 197         case F_DELETE:
 198                 if (aflag) {
 199                         if (argc != 0)
 200                                 usage();
 201                         search(0, nuke_entry);
 202                 } else {
 203                         if (argc < 1 || argc > 2)
 204                                 usage();
 205                         rtn = delete(argv[0], argv[1]);
 206                 }
 207                 break;
 208         case F_FILESET:
 209                 if (argc != 1)
 210                         usage();
 211                 rtn = file(argv[0]);
 212                 break;
 213         }
 214
 215         return(rtn);
 216 }
 217
 218 /*
 219  * Process a file to set standard arp entries
 220  */
 221 static int
 222 file(char *name)
 223 {
 224         FILE *fp;
 225         int i, retval;
 226         char line[100], arg[5][50], *args[5], *p;
 227
 228         if ((fp = fopen(name, "r")) == NULL)
 229                 errx(1, "cannot open %s", name);
 230         args[0] = &arg[0][0];
 231         args[1] = &arg[1][0];
 232         args[2] = &arg[2][0];
 233         args[3] = &arg[3][0];
 234         args[4] = &arg[4][0];
 235         retval = 0;
 236         while(fgets(line, 100, fp) != NULL) {
 237                 if ((p = strchr(line, '#')) != NULL)
 238                         *p = '\0';
 239                 for (p = line; isblank(*p); p++);
 240                 if (*p == '\n' || *p == '\0')
 241                         continue;
 242                 i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1],
 243                     arg[2], arg[3], arg[4]);
 244                 if (i < 2) {
 245                         warnx("bad line: %s", line);
 246                         retval = 1;
 247                         continue;
 248                 }
 249                 if (set(i, args))
 250                         retval = 1;
 251         }
 252         fclose(fp);
 253         return(retval);
 254 }
 255
 256 static void
 257 getsocket(void)
 258 {
 259         if (s < 0) {
 260                 s = socket(PF_ROUTE, SOCK_RAW, 0);
 261                 if (s < 0)
 262                         err(1, "socket");
 263         }
 264 }
 265
 266 /*
 267  * Set an individual arp entry
 268  */
 269 static int
 270 set(int argc, char **argv)
 271 {
 272         struct hostent *hp;
 273         struct sockaddr_inarp *addr = &sin_m;
 274         struct sockaddr_dl *sdl;
 275         struct rt_msghdr *rtm = &(m_rtmsg.m_rtm);
 276         struct ether_addr *ea;
 277         char *host = argv[0], *eaddr = argv[1];
 278
 279         getsocket();
 280         argc -= 2;
 281         argv += 2;
 282         sdl_m = blank_sdl;
 283         sin_m = blank_sin;
 284         addr->sin_addr.s_addr = inet_addr(host);
 285         if (addr->sin_addr.s_addr == INADDR_NONE) {
 286                 if (!(hp = gethostbyname(host))) {
 287                         warnx("%s: %s", host, hstrerror(h_errno));
 288                         return(1);
 289                 }
 290                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 291                     sizeof(addr->sin_addr));
 292         }
 293         doing_proxy = flags = proxy_only = expire_time = 0;
 294         while (argc-- > 0) {
 295                 if (strncmp(argv[0], "temp", 4) == 0) {
 296                         struct timespec sp;
 297
 298                         clock_gettime(CLOCK_MONOTONIC, &sp);
 299                         expire_time = sp.tv_sec + 20 * 60;
 300                 }
 301                 else if (strncmp(argv[0], "pub", 3) == 0) {
 302                         flags |= RTF_ANNOUNCE;
 303                         doing_proxy = 1;
 304                         if (argc && strncmp(argv[1], "only", 3) == 0) {
 305                                 proxy_only = 1;
 306                                 sin_m.sin_other = SIN_PROXY;
 307                                 argc--; argv++;
 308                         }
 309                 } else if (strncmp(argv[0], "trail", 5) == 0) {
 310                         printf("%s: Sending trailers is no longer supported\n",
 311                                 host);
 312                 }
 313                 argv++;
 314         }
 315         ea = (struct ether_addr *)LLADDR(&sdl_m);
 316         if (doing_proxy && !strcmp(eaddr, "auto")) {
 317                 if (!get_ether_addr(addr->sin_addr.s_addr, ea)) {
 318                         printf("no interface found for %s\n",
 319                                inet_ntoa(addr->sin_addr));
 320                         return(1);
 321                 }
 322                 sdl_m.sdl_alen = ETHER_ADDR_LEN;
 323         } else {
 324                 if (my_ether_aton(eaddr, ea) == 0)
 325                         sdl_m.sdl_alen = ETHER_ADDR_LEN;
 326         }
 327 tryagain:
 328         if (rtmsg(RTM_GET) < 0) {
 329                 warn("%s", host);
 330                 return(1);
 331         }
 332         addr = (struct sockaddr_inarp *)(rtm + 1);
 333         sdl = (struct sockaddr_dl *)(RT_ROUNDUP(addr->sin_len) + (char *)addr);
 334         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 335                 if (sdl->sdl_family == AF_LINK &&
 336                     (rtm->rtm_flags & RTF_LLINFO) &&
 337                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 338                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 339                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 340                 case IFT_CARP:
 341                         goto overwrite;
 342                 }
 343                 if (doing_proxy == 0) {
 344                         printf("set: can only proxy for %s\n", host);
 345                         return(1);
 346                 }
 347                 if (sin_m.sin_other & SIN_PROXY) {
 348                         printf("set: proxy entry exists for non 802 device\n");
 349                         return(1);
 350                 }
 351                 sin_m.sin_other = SIN_PROXY;
 352                 proxy_only = 1;
 353                 goto tryagain;
 354         }
 355 overwrite:
 356         if (sdl->sdl_family != AF_LINK) {
 357                 printf("cannot intuit interface index and type for %s\n", host);
 358                 return(1);
 359         }
 360         sdl_m.sdl_type = sdl->sdl_type;
 361         sdl_m.sdl_index = sdl->sdl_index;
 362         return(rtmsg(RTM_ADD));
 363 }
 364
 365 /*
 366  * Display an individual arp entry
 367  */
 368 static int
 369 get(char *host)
 370 {
 371         struct hostent *hp;
 372         struct sockaddr_inarp *addr = &sin_m;
 373
 374         sin_m = blank_sin;
 375         addr->sin_addr.s_addr = inet_addr(host);
 376         if (addr->sin_addr.s_addr == INADDR_NONE) {
 377                 if (!(hp = gethostbyname(host)))
 378                         errx(1, "%s: %s", host, hstrerror(h_errno));
 379                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 380                     sizeof(addr->sin_addr));
 381         }
 382         search(addr->sin_addr.s_addr, print_entry);
 383         if (found_entry == 0) {
 384                 printf("%s (%s) -- no entry",
 385                     host, inet_ntoa(addr->sin_addr));
 386                 if (rifname)
 387                         printf(" on %s", rifname);
 388                 printf("\n");
 389                 return(1);
 390         }
 391         return(0);
 392 }
 393
 394 /*
 395  * Delete an arp entry
 396  */
 397 static int
 398 delete(char *host, char *info)
 399 {
 400         struct hostent *hp;
 401         struct sockaddr_inarp *addr = &sin_m;
 402         struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 403         struct sockaddr_dl *sdl;
 404
 405         getsocket();
 406         sin_m = blank_sin;
 407         if (info) {
 408                 if (strncmp(info, "pub", 3) == 0)
 409                         sin_m.sin_other = SIN_PROXY;
 410                 else
 411                         usage();
 412         }
 413         addr->sin_addr.s_addr = inet_addr(host);
 414         if (addr->sin_addr.s_addr == INADDR_NONE) {
 415                 if (!(hp = gethostbyname(host))) {
 416                         warnx("%s: %s", host, hstrerror(h_errno));
 417                         return(1);
 418                 }
 419                 bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
 420                     sizeof(addr->sin_addr));
 421         }
 422 tryagain:
 423         if (rtmsg(RTM_GET) < 0) {
 424                 warn("%s", host);
 425                 return(1);
 426         }
 427         addr = (struct sockaddr_inarp *)(rtm + 1);
 428         sdl = (struct sockaddr_dl *)(RT_ROUNDUP(addr->sin_len) + (char *)addr);
 429         if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
 430                 if (sdl->sdl_family == AF_LINK &&
 431                     (rtm->rtm_flags & RTF_LLINFO) &&
 432                     !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
 433                 case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
 434                 case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
 435                 case IFT_CARP:
 436                         goto delete;
 437                 }
 438         }
 439         if (sin_m.sin_other & SIN_PROXY) {
 440                 fprintf(stderr, "delete: can't locate %s\n",host);
 441                 return(1);
 442         } else {
 443                 sin_m.sin_other = SIN_PROXY;
 444                 goto tryagain;
 445         }
 446 delete:
 447         if (sdl->sdl_family != AF_LINK) {
 448                 printf("cannot locate %s\n", host);
 449                 return(1);
 450         }
 451         if (aflag && (rtm->rtm_flags & RTF_STATIC)) {
 452                 sdl->sdl_alen = 0;
 453                 sdl->sdl_slen = 0;
 454                 if (rtmsg(RTM_CHANGE) == 0) {
 455                         printf("%s (%s) cleared\n",
 456                                 host, inet_ntoa(addr->sin_addr));
 457                         return(0);
 458                 }
 459         } else {
 460                 if (rtmsg(RTM_DELETE) == 0) {
 461                         printf("%s (%s) deleted\n",
 462                                 host, inet_ntoa(addr->sin_addr));
 463                         return(0);
 464                 }
 465         }
 466         return(1);
 467 }
 468
 469 /*
 470  * Search the arp table and do some action on matching entries
 471  */
 472 static void
 473 search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
 474         struct sockaddr_inarp *sin, struct rt_msghdr *rtm))
 475 {
 476         int mib[7];
 477         int miblen;
 478         size_t needed;
 479         char *lim, *buf, *next;
 480         struct rt_msghdr *rtm;
 481         struct sockaddr_inarp *sin2;
 482         struct sockaddr_dl *sdl;
 483
 484         mib[0] = CTL_NET;
 485         mib[1] = PF_ROUTE;
 486         mib[2] = 0;
 487         mib[3] = AF_INET;
 488         mib[4] = NET_RT_FLAGS;
 489         mib[5] = RTF_LLINFO;
 490         if (cpuflag >= 0) {
 491             mib[6] = cpuflag;
 492             miblen = 7;
 493         } else {
 494             miblen = 6;
 495         }
 496         if (sysctl(mib, miblen, NULL, &needed, NULL, 0) < 0)
 497                 errx(1, "route-sysctl-estimate");
 498         if ((buf = malloc(needed)) == NULL)
 499                 errx(1, "malloc");
 500         if (sysctl(mib, miblen, buf, &needed, NULL, 0) < 0)
 501                 errx(1, "actual retrieval of routing table");
 502         lim = buf + needed;
 503         for (next = buf; next < lim; next += rtm->rtm_msglen) {
 504                 rtm = (struct rt_msghdr *)next;
 505                 sin2 = (struct sockaddr_inarp *)(rtm + 1);
 506                 sdl = (struct sockaddr_dl *)((char *)sin2 +
 507                             RT_ROUNDUP(sin2->sin_len));
 508                 if (rifindex > 0 && rifindex != sdl->sdl_index)
 509                         continue;
 510                 if (addr) {
 511                         if (addr != sin2->sin_addr.s_addr)
 512                                 continue;
 513                         found_entry = 1;
 514                 }
 515                 (*action)(sdl, sin2, rtm);
 516         }
 517         free(buf);
 518 }
 519
 520 /*
 521  * Display an arp entry
 522  */
 523 static void
 524 print_entry(struct sockaddr_dl *sdl,
 525         struct sockaddr_inarp *addr, struct rt_msghdr *rtm)
 526 {
 527         const char *host;
 528         struct hostent *hp;
 529         char ifname[IF_NAMESIZE];
 530
 531         if (nflag == 0)
 532                 hp = gethostbyaddr(&(addr->sin_addr), sizeof(addr->sin_addr),
 533                     AF_INET);
 534         else
 535                 hp = NULL;
 536         if (hp)
 537                 host = hp->h_name;
 538         else {
 539                 host = "?";
 540                 if (h_errno == TRY_AGAIN)
 541                         nflag = 1;
 542         }
 543         printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
 544         if (sdl->sdl_alen)
 545                 printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
 546         else
 547                 printf("(incomplete)");
 548         if (if_indextoname(sdl->sdl_index, ifname) != NULL)
 549                 printf(" on %s", ifname);
 550         if (rtm->rtm_rmx.rmx_expire == 0)
 551                 printf(" permanent");
 552         if (addr->sin_other & SIN_PROXY)
 553                 printf(" published (proxy only)");
 554         if (rtm->rtm_addrs & RTA_NETMASK) {
 555                 addr = (struct sockaddr_inarp *)
 556                         (RT_ROUNDUP(sdl->sdl_len) + (char *)sdl);
 557                 if (addr->sin_addr.s_addr == 0xffffffff)
 558                         printf(" published");
 559                 if (addr->sin_len != 8)
 560                         printf("(weird)");
 561         }
 562         switch(sdl->sdl_type) {
 563             case IFT_ETHER:
 564                 printf(" [ethernet]");
 565                 break;
 566             case IFT_L2VLAN:
 567                 printf(" [vlan]");
 568                 break;
 569             case IFT_CARP:
 570                 printf(" [carp]");
 571             default:
 572                 break;
 573         }
 574
 575         printf("\n");
 576
 577 }
 578
 579 /*
 580  * Nuke an arp entry
 581  */
 582 static void
 583 nuke_entry(struct sockaddr_dl *sdl __unused,
 584         struct sockaddr_inarp *addr, struct rt_msghdr *rtm __unused)
 585 {
 586         char ip[20];
 587
 588         snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
 589         delete(ip, NULL);
 590 }
 591
 592 static int
 593 my_ether_aton(char *a, struct ether_addr *n)
 594 {
 595         struct ether_addr *ea;
 596
 597         if ((ea = ether_aton(a)) == NULL) {
 598                 warnx("invalid Ethernet address '%s'", a);
 599                 return(1);
 600         }
 601         *n = *ea;
 602         return(0);
 603 }
 604
 605 static void
 606 usage(void)
 607 {
 608         fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
 609                 "usage: arp [-n] [-c cpu] [-i interface] hostname",
 610                 "       arp [-n] [-c cpu] [-i interface] -a",
 611                 "       arp -d hostname [pub]",
 612                 "       arp -d [-i interface] -a",
 613                 "       arp -s hostname ether_addr [temp] [pub [only]]",
 614                 "       arp -S hostname ether_addr [temp] [pub [only]]",
 615                 "       arp -f filename");
 616         exit(1);
 617 }
 618
 619 static int
 620 rtmsg(int cmd)
 621 {
 622         static int seq;
 623         int rlen;
 624         struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
 625         char *cp = m_rtmsg.m_space;
 626         int l;
 627
 628         errno = 0;
 629         if (cmd == RTM_DELETE || cmd == RTM_CHANGE)
 630                 goto doit;
 631         bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
 632         rtm->rtm_flags = flags;
 633         rtm->rtm_version = RTM_VERSION;
 634
 635         switch (cmd) {
 636         default:
 637                 errx(1, "internal wrong cmd");
 638         case RTM_ADD:
 639                 rtm->rtm_addrs |= RTA_GATEWAY;
 640                 rtm->rtm_rmx.rmx_expire = expire_time;
 641                 rtm->rtm_inits = RTV_EXPIRE;
 642                 rtm->rtm_flags |= (RTF_HOST | RTF_STATIC);
 643                 sin_m.sin_other = 0;
 644                 if (doing_proxy) {
 645                         if (proxy_only)
 646                                 sin_m.sin_other = SIN_PROXY;
 647                         else {
 648                                 rtm->rtm_addrs |= RTA_NETMASK;
 649                                 rtm->rtm_flags &= ~RTF_HOST;
 650                         }
 651                 }
 652                 /* FALLTHROUGH */
 653         case RTM_GET:
 654                 rtm->rtm_addrs |= RTA_DST;
 655         }
 656
 657 #define NEXTADDR(w, s)                                  \
 658         if (rtm->rtm_addrs & (w)) {                     \
 659                 bcopy((char *)&s, cp, sizeof(s));       \
 660                 cp += RT_ROUNDUP(sizeof(s));            \
 661         }
 662
 663         NEXTADDR(RTA_DST, sin_m);
 664         NEXTADDR(RTA_GATEWAY, sdl_m);
 665         NEXTADDR(RTA_NETMASK, so_mask);
 666
 667         rtm->rtm_msglen = cp - (char *)&m_rtmsg;
 668 doit:
 669         l = rtm->rtm_msglen;
 670         rtm->rtm_seq = ++seq;
 671         rtm->rtm_type = cmd;
 672         if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
 673                 if (errno != ESRCH || (cmd != RTM_DELETE && cmd != RTM_CHANGE)) {
 674                         warn("writing to routing socket");
 675                         return(-1);
 676                 }
 677         }
 678         do {
 679                 l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
 680         } while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
 681         if (l < 0)
 682                 warn("read from routing socket");
 683         return(0);
 684 }
 685
 686 /*
 687  * get_ether_addr - get the hardware address of an interface on the
 688  * the same subnet as ipaddr.
 689  */
 690 #define MAX_IFS         32
 691
 692 static int
 693 get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr)
 694 {
 695         struct ifreq *ifr, *ifend, *ifp;
 696         u_int32_t ina, mask;
 697         struct sockaddr_dl *dla;
 698         struct ifreq ifreq;
 699         struct ifconf ifc;
 700         struct ifreq ifs[MAX_IFS];
 701         int sock;
 702
 703         sock = socket(AF_INET, SOCK_DGRAM, 0);
 704         if (sock < 0)
 705                 err(1, "socket");
 706
 707         ifc.ifc_len = sizeof(ifs);
 708         ifc.ifc_req = ifs;
 709         if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
 710                 warnx("ioctl(SIOCGIFCONF)");
 711                 close(sock);
 712                 return(0);
 713         }
 714
 715         /*
 716         * Scan through looking for an interface with an Internet
 717         * address on the same subnet as `ipaddr'.
 718         */
 719         ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
 720         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 721                 if (ifr->ifr_addr.sa_family == AF_INET) {
 722                         ina = ((struct sockaddr_in *)
 723                                 &ifr->ifr_addr)->sin_addr.s_addr;
 724                         strncpy(ifreq.ifr_name, ifr->ifr_name,
 725                                 sizeof(ifreq.ifr_name));
 726                         /*
 727                          * Check that the interface is up,
 728                          * and not point-to-point or loopback.
 729                          */
 730                         if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
 731                                 continue;
 732                         if ((ifreq.ifr_flags &
 733                              (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
 734                                         IFF_LOOPBACK|IFF_NOARP))
 735                              != (IFF_UP|IFF_BROADCAST))
 736                                 goto nextif;
 737                         /*
 738                          * Get its netmask and check that it's on
 739                          * the right subnet.
 740                          */
 741                         if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
 742                                 continue;
 743                         mask = ((struct sockaddr_in *)
 744                                 &ifreq.ifr_addr)->sin_addr.s_addr;
 745                         if ((ipaddr & mask) != (ina & mask))
 746                                 goto nextif;
 747                         break;
 748                 }
 749 nextif:
 750                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 751                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 752         }
 753
 754         if (ifr >= ifend) {
 755                 close(sock);
 756                 return(0);
 757         }
 758
 759         /*
 760         * Now scan through again looking for a link-level address
 761         * for this interface.
 762         */
 763         ifp = ifr;
 764         for (ifr = ifc.ifc_req; ifr < ifend; ) {
 765                 if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0
 766                     && ifr->ifr_addr.sa_family == AF_LINK) {
 767                         /*
 768                          * Found the link-level address - copy it out
 769                          */
 770                         dla = (struct sockaddr_dl *) &ifr->ifr_addr;
 771                         memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
 772                         close (sock);
 773                         printf("using interface %s for proxy with address ",
 774                                 ifp->ifr_name);
 775                         printf("%s\n", ether_ntoa(hwaddr));
 776                         return(dla->sdl_alen);
 777                 }
 778                 ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
 779                     + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
 780         }
 781         return(0);
 782 }