xref: /freebsd/usr.sbin/arp/arp.c (revision 8d20be1e22095c27faf8fe8b2f0d089739cc742e)
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  * 4. 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 
33 #if 0
34 #ifndef lint
35 static char const copyright[] =
36 "@(#) Copyright (c) 1984, 1993\n\
37 	The Regents of the University of California.  All rights reserved.\n";
38 #endif /* not lint */
39 
40 #ifndef lint
41 static char const sccsid[] = "@(#)from: arp.c	8.2 (Berkeley) 1/2/94";
42 #endif /* not lint */
43 #endif
44 #include <sys/cdefs.h>
45 __FBSDID("$FreeBSD$");
46 
47 /*
48  * arp - display, set, and delete arp table entries
49  */
50 
51 
52 #include <sys/param.h>
53 #include <sys/file.h>
54 #include <sys/socket.h>
55 #include <sys/sockio.h>
56 #include <sys/sysctl.h>
57 #include <sys/ioctl.h>
58 #include <sys/time.h>
59 
60 #include <net/if.h>
61 #include <net/if_dl.h>
62 #include <net/if_types.h>
63 #include <net/route.h>
64 #include <net/iso88025.h>
65 
66 #include <netinet/in.h>
67 #include <netinet/if_ether.h>
68 
69 #include <arpa/inet.h>
70 
71 #include <ctype.h>
72 #include <err.h>
73 #include <errno.h>
74 #include <netdb.h>
75 #include <nlist.h>
76 #include <paths.h>
77 #include <stdio.h>
78 #include <stdlib.h>
79 #include <string.h>
80 #include <strings.h>
81 #include <unistd.h>
82 
83 typedef void (action_fn)(struct sockaddr_dl *sdl,
84 	struct sockaddr_in *s_in, struct rt_msghdr *rtm);
85 
86 static int search(u_long addr, action_fn *action);
87 static action_fn print_entry;
88 static action_fn nuke_entry;
89 
90 static int delete(char *host);
91 static void usage(void);
92 static int set(int argc, char **argv);
93 static int get(char *host);
94 static int file(char *name);
95 static struct rt_msghdr *rtmsg(int cmd,
96     struct sockaddr_in *dst, struct sockaddr_dl *sdl);
97 static int get_ether_addr(in_addr_t ipaddr, struct ether_addr *hwaddr);
98 static struct sockaddr_in *getaddr(char *host);
99 static int valid_type(int type);
100 
101 static int nflag;	/* no reverse dns lookups */
102 static char *rifname;
103 
104 static time_t	expire_time;
105 static int	flags, doing_proxy;
106 
107 /* which function we're supposed to do */
108 #define F_GET		1
109 #define F_SET		2
110 #define F_FILESET	3
111 #define F_REPLACE	4
112 #define F_DELETE	5
113 
114 #define SETFUNC(f)	{ if (func) usage(); func = (f); }
115 
116 int
117 main(int argc, char *argv[])
118 {
119 	int ch, func = 0;
120 	int rtn = 0;
121 	int aflag = 0;	/* do it for all entries */
122 
123 	while ((ch = getopt(argc, argv, "andfsSi:")) != -1)
124 		switch(ch) {
125 		case 'a':
126 			aflag = 1;
127 			break;
128 		case 'd':
129 			SETFUNC(F_DELETE);
130 			break;
131 		case 'n':
132 			nflag = 1;
133 			break;
134 		case 'S':
135 			SETFUNC(F_REPLACE);
136 			break;
137 		case 's':
138 			SETFUNC(F_SET);
139 			break;
140 		case 'f' :
141 			SETFUNC(F_FILESET);
142 			break;
143 		case 'i':
144 			rifname = optarg;
145 			break;
146 		case '?':
147 		default:
148 			usage();
149 		}
150 	argc -= optind;
151 	argv += optind;
152 
153 	if (!func)
154 		func = F_GET;
155 	if (rifname) {
156 		if (func != F_GET && !(func == F_DELETE && aflag))
157 			errx(1, "-i not applicable to this operation");
158 		if (if_nametoindex(rifname) == 0) {
159 			if (errno == ENXIO)
160 				errx(1, "interface %s does not exist", rifname);
161 			else
162 				err(1, "if_nametoindex(%s)", rifname);
163 		}
164 	}
165 	switch (func) {
166 	case F_GET:
167 		if (aflag) {
168 			if (argc != 0)
169 				usage();
170 			search(0, print_entry);
171 		} else {
172 			if (argc != 1)
173 				usage();
174 			rtn = get(argv[0]);
175 		}
176 		break;
177 	case F_SET:
178 	case F_REPLACE:
179 		if (argc < 2 || argc > 6)
180 			usage();
181 		if (func == F_REPLACE)
182 			(void)delete(argv[0]);
183 		rtn = set(argc, argv) ? 1 : 0;
184 		break;
185 	case F_DELETE:
186 		if (aflag) {
187 			if (argc != 0)
188 				usage();
189 			search(0, nuke_entry);
190 		} else {
191 			if (argc != 1)
192 				usage();
193 			rtn = delete(argv[0]);
194 		}
195 		break;
196 	case F_FILESET:
197 		if (argc != 1)
198 			usage();
199 		rtn = file(argv[0]);
200 		break;
201 	}
202 
203 	return (rtn);
204 }
205 
206 /*
207  * Process a file to set standard arp entries
208  */
209 static int
210 file(char *name)
211 {
212 	FILE *fp;
213 	int i, retval;
214 	char line[100], arg[5][50], *args[5], *p;
215 
216 	if ((fp = fopen(name, "r")) == NULL)
217 		err(1, "cannot open %s", name);
218 	args[0] = &arg[0][0];
219 	args[1] = &arg[1][0];
220 	args[2] = &arg[2][0];
221 	args[3] = &arg[3][0];
222 	args[4] = &arg[4][0];
223 	retval = 0;
224 	while(fgets(line, sizeof(line), fp) != NULL) {
225 		if ((p = strchr(line, '#')) != NULL)
226 			*p = '\0';
227 		for (p = line; isblank(*p); p++);
228 		if (*p == '\n' || *p == '\0')
229 			continue;
230 		i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1],
231 		    arg[2], arg[3], arg[4]);
232 		if (i < 2) {
233 			warnx("bad line: %s", line);
234 			retval = 1;
235 			continue;
236 		}
237 		if (set(i, args))
238 			retval = 1;
239 	}
240 	fclose(fp);
241 	return (retval);
242 }
243 
244 /*
245  * Given a hostname, fills up a (static) struct sockaddr_in with
246  * the address of the host and returns a pointer to the
247  * structure.
248  */
249 static struct sockaddr_in *
250 getaddr(char *host)
251 {
252 	struct hostent *hp;
253 	static struct sockaddr_in reply;
254 
255 	bzero(&reply, sizeof(reply));
256 	reply.sin_len = sizeof(reply);
257 	reply.sin_family = AF_INET;
258 	reply.sin_addr.s_addr = inet_addr(host);
259 	if (reply.sin_addr.s_addr == INADDR_NONE) {
260 		if (!(hp = gethostbyname(host))) {
261 			warnx("%s: %s", host, hstrerror(h_errno));
262 			return (NULL);
263 		}
264 		bcopy((char *)hp->h_addr, (char *)&reply.sin_addr,
265 			sizeof reply.sin_addr);
266 	}
267 	return (&reply);
268 }
269 
270 /*
271  * Returns true if the type is a valid one for ARP.
272  */
273 static int
274 valid_type(int type)
275 {
276 
277 	switch (type) {
278 	case IFT_ETHER:
279 	case IFT_FDDI:
280 	case IFT_ISO88023:
281 	case IFT_ISO88024:
282 	case IFT_ISO88025:
283 	case IFT_L2VLAN:
284 	case IFT_BRIDGE:
285 		return (1);
286 	default:
287 		return (0);
288 	}
289 }
290 
291 /*
292  * Set an individual arp entry
293  */
294 static int
295 set(int argc, char **argv)
296 {
297 	struct sockaddr_in *addr;
298 	struct sockaddr_in *dst;	/* what are we looking for */
299 	struct sockaddr_dl *sdl;
300 	struct rt_msghdr *rtm;
301 	struct ether_addr *ea;
302 	char *host = argv[0], *eaddr = argv[1];
303 	struct sockaddr_dl sdl_m;
304 
305 	argc -= 2;
306 	argv += 2;
307 
308 	bzero(&sdl_m, sizeof(sdl_m));
309 	sdl_m.sdl_len = sizeof(sdl_m);
310 	sdl_m.sdl_family = AF_LINK;
311 
312 	dst = getaddr(host);
313 	if (dst == NULL)
314 		return (1);
315 	doing_proxy = flags = expire_time = 0;
316 	while (argc-- > 0) {
317 		if (strncmp(argv[0], "temp", 4) == 0) {
318 			struct timespec tp;
319 			int max_age;
320 			size_t len = sizeof(max_age);
321 
322 			clock_gettime(CLOCK_MONOTONIC, &tp);
323 			if (sysctlbyname("net.link.ether.inet.max_age",
324 			    &max_age, &len, NULL, 0) != 0)
325 				err(1, "sysctlbyname");
326 			expire_time = tp.tv_sec + max_age;
327 		} else if (strncmp(argv[0], "pub", 3) == 0) {
328 			flags |= RTF_ANNOUNCE;
329 			doing_proxy = 1;
330 			if (argc && strncmp(argv[1], "only", 3) == 0) {
331 				/*
332 				 * Compatibility: in pre FreeBSD 8 times
333 				 * the "only" keyword used to mean that
334 				 * an ARP entry should be announced, but
335 				 * not installed into routing table.
336 				 */
337 				argc--; argv++;
338 			}
339 		} else if (strncmp(argv[0], "blackhole", 9) == 0) {
340 			if (flags & RTF_REJECT) {
341 				printf("Choose one of blackhole or reject, not both.\n");
342 			}
343 			flags |= RTF_BLACKHOLE;
344 		} else if (strncmp(argv[0], "reject", 6) == 0) {
345 			if (flags & RTF_BLACKHOLE) {
346 				printf("Choose one of blackhole or reject, not both.\n");
347 			}
348 			flags |= RTF_REJECT;
349 		} else if (strncmp(argv[0], "trail", 5) == 0) {
350 			/* XXX deprecated and undocumented feature */
351 			printf("%s: Sending trailers is no longer supported\n",
352 				host);
353 		}
354 		argv++;
355 	}
356 	ea = (struct ether_addr *)LLADDR(&sdl_m);
357 	if (doing_proxy && !strcmp(eaddr, "auto")) {
358 		if (!get_ether_addr(dst->sin_addr.s_addr, ea)) {
359 			printf("no interface found for %s\n",
360 			       inet_ntoa(dst->sin_addr));
361 			return (1);
362 		}
363 		sdl_m.sdl_alen = ETHER_ADDR_LEN;
364 	} else {
365 		struct ether_addr *ea1 = ether_aton(eaddr);
366 
367 		if (ea1 == NULL) {
368 			warnx("invalid Ethernet address '%s'", eaddr);
369 			return (1);
370 		} else {
371 			*ea = *ea1;
372 			sdl_m.sdl_alen = ETHER_ADDR_LEN;
373 		}
374 	}
375 
376 	/*
377 	 * In the case a proxy-arp entry is being added for
378 	 * a remote end point, the RTF_ANNOUNCE flag in the
379 	 * RTM_GET command is an indication to the kernel
380 	 * routing code that the interface associated with
381 	 * the prefix route covering the local end of the
382 	 * PPP link should be returned, on which ARP applies.
383 	 */
384 	rtm = rtmsg(RTM_GET, dst, &sdl_m);
385 	if (rtm == NULL) {
386 		warn("%s", host);
387 		return (1);
388 	}
389 	addr = (struct sockaddr_in *)(rtm + 1);
390 	sdl = (struct sockaddr_dl *)(SA_SIZE(addr) + (char *)addr);
391 
392 	if ((sdl->sdl_family != AF_LINK) ||
393 	    (rtm->rtm_flags & RTF_GATEWAY) ||
394 	    !valid_type(sdl->sdl_type)) {
395 		printf("cannot intuit interface index and type for %s\n", host);
396 		return (1);
397 	}
398 	sdl_m.sdl_type = sdl->sdl_type;
399 	sdl_m.sdl_index = sdl->sdl_index;
400 	return (rtmsg(RTM_ADD, dst, &sdl_m) == NULL);
401 }
402 
403 /*
404  * Display an individual arp entry
405  */
406 static int
407 get(char *host)
408 {
409 	struct sockaddr_in *addr;
410 
411 	addr = getaddr(host);
412 	if (addr == NULL)
413 		return (1);
414 	if (0 == search(addr->sin_addr.s_addr, print_entry)) {
415 		printf("%s (%s) -- no entry",
416 		    host, inet_ntoa(addr->sin_addr));
417 		if (rifname)
418 			printf(" on %s", rifname);
419 		printf("\n");
420 		return (1);
421 	}
422 	return (0);
423 }
424 
425 /*
426  * Delete an arp entry
427  */
428 static int
429 delete(char *host)
430 {
431 	struct sockaddr_in *addr, *dst;
432 	struct rt_msghdr *rtm;
433 	struct sockaddr_dl *sdl;
434 	struct sockaddr_dl sdl_m;
435 
436 	dst = getaddr(host);
437 	if (dst == NULL)
438 		return (1);
439 
440 	/*
441 	 * Perform a regular entry delete first.
442 	 */
443 	flags &= ~RTF_ANNOUNCE;
444 
445 	/*
446 	 * setup the data structure to notify the kernel
447 	 * it is the ARP entry the RTM_GET is interested
448 	 * in
449 	 */
450 	bzero(&sdl_m, sizeof(sdl_m));
451 	sdl_m.sdl_len = sizeof(sdl_m);
452 	sdl_m.sdl_family = AF_LINK;
453 
454 	for (;;) {	/* try twice */
455 		rtm = rtmsg(RTM_GET, dst, &sdl_m);
456 		if (rtm == NULL) {
457 			warn("%s", host);
458 			return (1);
459 		}
460 		addr = (struct sockaddr_in *)(rtm + 1);
461 		sdl = (struct sockaddr_dl *)(SA_SIZE(addr) + (char *)addr);
462 
463 		/*
464 		 * With the new L2/L3 restructure, the route
465 		 * returned is a prefix route. The important
466 		 * piece of information from the previous
467 		 * RTM_GET is the interface index. In the
468 		 * case of ECMP, the kernel will traverse
469 		 * the route group for the given entry.
470 		 */
471 		if (sdl->sdl_family == AF_LINK &&
472 		    !(rtm->rtm_flags & RTF_GATEWAY) &&
473 		    valid_type(sdl->sdl_type) ) {
474 			addr->sin_addr.s_addr = dst->sin_addr.s_addr;
475 			break;
476 		}
477 
478 		/*
479 		 * Regualar entry delete failed, now check if there
480 		 * is a proxy-arp entry to remove.
481 		 */
482 		if (flags & RTF_ANNOUNCE) {
483 			fprintf(stderr, "delete: cannot locate %s\n",host);
484 			return (1);
485 		}
486 
487 		flags |= RTF_ANNOUNCE;
488 	}
489 	rtm->rtm_flags |= RTF_LLDATA;
490 	if (rtmsg(RTM_DELETE, dst, NULL) != NULL) {
491 		printf("%s (%s) deleted\n", host, inet_ntoa(addr->sin_addr));
492 		return (0);
493 	}
494 	return (1);
495 }
496 
497 
498 /*
499  * Search the arp table and do some action on matching entries
500  */
501 static int
502 search(u_long addr, action_fn *action)
503 {
504 	int mib[6];
505 	size_t needed;
506 	char *lim, *buf, *next;
507 	struct rt_msghdr *rtm;
508 	struct sockaddr_in *sin2;
509 	struct sockaddr_dl *sdl;
510 	char ifname[IF_NAMESIZE];
511 	int st, found_entry = 0;
512 
513 	mib[0] = CTL_NET;
514 	mib[1] = PF_ROUTE;
515 	mib[2] = 0;
516 	mib[3] = AF_INET;
517 	mib[4] = NET_RT_FLAGS;
518 #ifdef RTF_LLINFO
519 	mib[5] = RTF_LLINFO;
520 #else
521 	mib[5] = 0;
522 #endif
523 	if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
524 		err(1, "route-sysctl-estimate");
525 	if (needed == 0)	/* empty table */
526 		return 0;
527 	buf = NULL;
528 	for (;;) {
529 		buf = reallocf(buf, needed);
530 		if (buf == NULL)
531 			errx(1, "could not reallocate memory");
532 		st = sysctl(mib, 6, buf, &needed, NULL, 0);
533 		if (st == 0 || errno != ENOMEM)
534 			break;
535 		needed += needed / 8;
536 	}
537 	if (st == -1)
538 		err(1, "actual retrieval of routing table");
539 	lim = buf + needed;
540 	for (next = buf; next < lim; next += rtm->rtm_msglen) {
541 		rtm = (struct rt_msghdr *)next;
542 		sin2 = (struct sockaddr_in *)(rtm + 1);
543 		sdl = (struct sockaddr_dl *)((char *)sin2 + SA_SIZE(sin2));
544 		if (rifname && if_indextoname(sdl->sdl_index, ifname) &&
545 		    strcmp(ifname, rifname))
546 			continue;
547 		if (addr) {
548 			if (addr != sin2->sin_addr.s_addr)
549 				continue;
550 			found_entry = 1;
551 		}
552 		(*action)(sdl, sin2, rtm);
553 	}
554 	free(buf);
555 	return (found_entry);
556 }
557 
558 /*
559  * Display an arp entry
560  */
561 static char lifname[IF_NAMESIZE];
562 static int64_t lifindex = -1;
563 
564 static void
565 print_entry(struct sockaddr_dl *sdl,
566 	struct sockaddr_in *addr, struct rt_msghdr *rtm)
567 {
568 	const char *host;
569 	struct hostent *hp;
570 	struct iso88025_sockaddr_dl_data *trld;
571 	int seg;
572 
573 	if (nflag == 0)
574 		hp = gethostbyaddr((caddr_t)&(addr->sin_addr),
575 		    sizeof addr->sin_addr, AF_INET);
576 	else
577 		hp = 0;
578 	if (hp)
579 		host = hp->h_name;
580 	else {
581 		host = "?";
582 		if (h_errno == TRY_AGAIN)
583 			nflag = 1;
584 	}
585 	printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
586 	if (sdl->sdl_alen) {
587 		if ((sdl->sdl_type == IFT_ETHER ||
588 		    sdl->sdl_type == IFT_L2VLAN ||
589 		    sdl->sdl_type == IFT_BRIDGE) &&
590 		    sdl->sdl_alen == ETHER_ADDR_LEN)
591 			printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
592 		else {
593 			int n = sdl->sdl_nlen > 0 ? sdl->sdl_nlen + 1 : 0;
594 
595 			printf("%s", link_ntoa(sdl) + n);
596 		}
597 	} else
598 		printf("(incomplete)");
599 	if (sdl->sdl_index != lifindex &&
600 	    if_indextoname(sdl->sdl_index, lifname) != NULL) {
601         	lifindex = sdl->sdl_index;
602 		printf(" on %s", lifname);
603         } else if (sdl->sdl_index == lifindex)
604 		printf(" on %s", lifname);
605 	if (rtm->rtm_rmx.rmx_expire == 0)
606 		printf(" permanent");
607 	else {
608 		static struct timespec tp;
609 		if (tp.tv_sec == 0)
610 			clock_gettime(CLOCK_MONOTONIC, &tp);
611 		if ((expire_time = rtm->rtm_rmx.rmx_expire - tp.tv_sec) > 0)
612 			printf(" expires in %d seconds", (int)expire_time);
613 		else
614 			printf(" expired");
615 	}
616 	if (rtm->rtm_flags & RTF_ANNOUNCE)
617 		printf(" published");
618 	switch(sdl->sdl_type) {
619 	case IFT_ETHER:
620                 printf(" [ethernet]");
621                 break;
622 	case IFT_ISO88025:
623                 printf(" [token-ring]");
624 		trld = SDL_ISO88025(sdl);
625 		if (trld->trld_rcf != 0) {
626 			printf(" rt=%x", ntohs(trld->trld_rcf));
627 			for (seg = 0;
628 			     seg < ((TR_RCF_RIFLEN(trld->trld_rcf) - 2 ) / 2);
629 			     seg++)
630 				printf(":%x", ntohs(*(trld->trld_route[seg])));
631 		}
632                 break;
633 	case IFT_FDDI:
634                 printf(" [fddi]");
635                 break;
636 	case IFT_ATM:
637                 printf(" [atm]");
638                 break;
639 	case IFT_L2VLAN:
640 		printf(" [vlan]");
641 		break;
642 	case IFT_IEEE1394:
643                 printf(" [firewire]");
644                 break;
645 	case IFT_BRIDGE:
646 		printf(" [bridge]");
647 		break;
648 	default:
649 		break;
650         }
651 
652 	printf("\n");
653 
654 }
655 
656 /*
657  * Nuke an arp entry
658  */
659 static void
660 nuke_entry(struct sockaddr_dl *sdl __unused,
661 	struct sockaddr_in *addr, struct rt_msghdr *rtm __unused)
662 {
663 	char ip[20];
664 
665 	snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
666 	delete(ip);
667 }
668 
669 static void
670 usage(void)
671 {
672 	fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
673 		"usage: arp [-n] [-i interface] hostname",
674 		"       arp [-n] [-i interface] -a",
675 		"       arp -d hostname [pub]",
676 		"       arp -d [-i interface] -a",
677 		"       arp -s hostname ether_addr [temp] [reject | blackhole] [pub [only]]",
678 		"       arp -S hostname ether_addr [temp] [reject | blackhole] [pub [only]]",
679 		"       arp -f filename");
680 	exit(1);
681 }
682 
683 static struct rt_msghdr *
684 rtmsg(int cmd, struct sockaddr_in *dst, struct sockaddr_dl *sdl)
685 {
686 	static int seq;
687 	int rlen;
688 	int l;
689 	struct sockaddr_in so_mask, *som = &so_mask;
690 	static int s = -1;
691 	static pid_t pid;
692 
693 	static struct	{
694 		struct	rt_msghdr m_rtm;
695 		char	m_space[512];
696 	}	m_rtmsg;
697 
698 	struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
699 	char *cp = m_rtmsg.m_space;
700 
701 	if (s < 0) {	/* first time: open socket, get pid */
702 		s = socket(PF_ROUTE, SOCK_RAW, 0);
703 		if (s < 0)
704 			err(1, "socket");
705 		pid = getpid();
706 	}
707 	bzero(&so_mask, sizeof(so_mask));
708 	so_mask.sin_len = 8;
709 	so_mask.sin_addr.s_addr = 0xffffffff;
710 
711 	errno = 0;
712 	/*
713 	 * XXX RTM_DELETE relies on a previous RTM_GET to fill the buffer
714 	 * appropriately.
715 	 */
716 	if (cmd == RTM_DELETE)
717 		goto doit;
718 	bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
719 	rtm->rtm_flags = flags;
720 	rtm->rtm_version = RTM_VERSION;
721 
722 	switch (cmd) {
723 	default:
724 		errx(1, "internal wrong cmd");
725 	case RTM_ADD:
726 		rtm->rtm_addrs |= RTA_GATEWAY;
727 		rtm->rtm_rmx.rmx_expire = expire_time;
728 		rtm->rtm_inits = RTV_EXPIRE;
729 		rtm->rtm_flags |= (RTF_HOST | RTF_STATIC | RTF_LLDATA);
730 		if (doing_proxy) {
731 			rtm->rtm_addrs |= RTA_NETMASK;
732 			rtm->rtm_flags &= ~RTF_HOST;
733 		}
734 		/* FALLTHROUGH */
735 	case RTM_GET:
736 		rtm->rtm_addrs |= RTA_DST;
737 	}
738 #define NEXTADDR(w, s)					   \
739 	do {						   \
740 		if ((s) != NULL && rtm->rtm_addrs & (w)) { \
741 			bcopy((s), cp, sizeof(*(s)));	   \
742 			cp += SA_SIZE(s);		   \
743 		}					   \
744 	} while (0)
745 
746 	NEXTADDR(RTA_DST, dst);
747 	NEXTADDR(RTA_GATEWAY, sdl);
748 	NEXTADDR(RTA_NETMASK, som);
749 
750 	rtm->rtm_msglen = cp - (char *)&m_rtmsg;
751 doit:
752 	l = rtm->rtm_msglen;
753 	rtm->rtm_seq = ++seq;
754 	rtm->rtm_type = cmd;
755 	if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
756 		if (errno != ESRCH || cmd != RTM_DELETE) {
757 			warn("writing to routing socket");
758 			return (NULL);
759 		}
760 	}
761 	do {
762 		l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
763 	} while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
764 	if (l < 0)
765 		warn("read from routing socket");
766 	return (rtm);
767 }
768 
769 /*
770  * get_ether_addr - get the hardware address of an interface on the
771  * the same subnet as ipaddr.
772  */
773 #define MAX_IFS		32
774 
775 static int
776 get_ether_addr(in_addr_t ipaddr, struct ether_addr *hwaddr)
777 {
778 	struct ifreq *ifr, *ifend, *ifp;
779 	in_addr_t ina, mask;
780 	struct sockaddr_dl *dla;
781 	struct ifreq ifreq;
782 	struct ifconf ifc;
783 	struct ifreq ifs[MAX_IFS];
784 	int sock;
785 	int retval = 0;
786 
787 	sock = socket(AF_INET, SOCK_DGRAM, 0);
788 	if (sock < 0)
789 		err(1, "socket");
790 
791 	ifc.ifc_len = sizeof(ifs);
792 	ifc.ifc_req = ifs;
793 	if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
794 		warnx("ioctl(SIOCGIFCONF)");
795 		goto done;
796 	}
797 
798 #define NEXTIFR(i)						\
799     ((struct ifreq *)((char *)&(i)->ifr_addr			\
800 	+ MAX((i)->ifr_addr.sa_len, sizeof((i)->ifr_addr))) )
801 
802 	/*
803 	 * Scan through looking for an interface with an Internet
804 	 * address on the same subnet as `ipaddr'.
805 	 */
806 	ifend = (struct ifreq *)(ifc.ifc_buf + ifc.ifc_len);
807 	for (ifr = ifc.ifc_req; ifr < ifend; ifr = NEXTIFR(ifr) ) {
808 		if (ifr->ifr_addr.sa_family != AF_INET)
809 			continue;
810 		strncpy(ifreq.ifr_name, ifr->ifr_name,
811 			sizeof(ifreq.ifr_name));
812 		ifreq.ifr_addr = ifr->ifr_addr;
813 		/*
814 		 * Check that the interface is up,
815 		 * and not point-to-point or loopback.
816 		 */
817 		if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
818 			continue;
819 		if ((ifreq.ifr_flags &
820 		     (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
821 				IFF_LOOPBACK|IFF_NOARP))
822 		     != (IFF_UP|IFF_BROADCAST))
823 			continue;
824 		/*
825 		 * Get its netmask and check that it's on
826 		 * the right subnet.
827 		 */
828 		if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
829 			continue;
830 		mask = ((struct sockaddr_in *)
831 			&ifreq.ifr_addr)->sin_addr.s_addr;
832 		ina = ((struct sockaddr_in *)
833 			&ifr->ifr_addr)->sin_addr.s_addr;
834 		if ((ipaddr & mask) == (ina & mask))
835 			break; /* ok, we got it! */
836 	}
837 
838 	if (ifr >= ifend)
839 		goto done;
840 
841 	/*
842 	 * Now scan through again looking for a link-level address
843 	 * for this interface.
844 	 */
845 	ifp = ifr;
846 	for (ifr = ifc.ifc_req; ifr < ifend; ifr = NEXTIFR(ifr))
847 		if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0 &&
848 		    ifr->ifr_addr.sa_family == AF_LINK)
849 			break;
850 	if (ifr >= ifend)
851 		goto done;
852 	/*
853 	 * Found the link-level address - copy it out
854 	 */
855 	dla = (struct sockaddr_dl *) &ifr->ifr_addr;
856 	memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
857 	printf("using interface %s for proxy with address ",
858 		ifp->ifr_name);
859 	printf("%s\n", ether_ntoa(hwaddr));
860 	retval = dla->sdl_alen;
861 done:
862 	close(sock);
863 	return (retval);
864 }
865