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
35static 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
41static 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
83typedef void (action_fn)(struct sockaddr_dl *sdl,
84	struct sockaddr_in *s_in, struct rt_msghdr *rtm);
85
86static int search(u_long addr, action_fn *action);
87static action_fn print_entry;
88static action_fn nuke_entry;
89
90static int delete(char *host);
91static void usage(void);
92static int set(int argc, char **argv);
93static int get(char *host);
94static int file(char *name);
95static struct rt_msghdr *rtmsg(int cmd,
96    struct sockaddr_in *dst, struct sockaddr_dl *sdl);
97static int get_ether_addr(in_addr_t ipaddr, struct ether_addr *hwaddr);
98static struct sockaddr_in *getaddr(char *host);
99static int valid_type(int type);
100
101static int nflag;	/* no reverse dns lookups */
102static char *rifname;
103
104static time_t	expire_time;
105static int	flags, doing_proxy;
106
107struct if_nameindex *ifnameindex;
108
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 SETFUNC(f)	{ if (func) usage(); func = (f); }
117
118int
119main(int argc, char *argv[])
120{
121	int ch, func = 0;
122	int rtn = 0;
123	int aflag = 0;	/* do it for all entries */
124
125	while ((ch = getopt(argc, argv, "andfsSi:")) != -1)
126		switch(ch) {
127		case 'a':
128			aflag = 1;
129			break;
130		case 'd':
131			SETFUNC(F_DELETE);
132			break;
133		case 'n':
134			nflag = 1;
135			break;
136		case 'S':
137			SETFUNC(F_REPLACE);
138			break;
139		case 's':
140			SETFUNC(F_SET);
141			break;
142		case 'f' :
143			SETFUNC(F_FILESET);
144			break;
145		case 'i':
146			rifname = optarg;
147			break;
148		case '?':
149		default:
150			usage();
151		}
152	argc -= optind;
153	argv += optind;
154
155	if (!func)
156		func = F_GET;
157	if (rifname) {
158		if (func != F_GET && !(func == F_DELETE && aflag))
159			errx(1, "-i not applicable to this operation");
160		if (if_nametoindex(rifname) == 0) {
161			if (errno == ENXIO)
162				errx(1, "interface %s does not exist", rifname);
163			else
164				err(1, "if_nametoindex(%s)", rifname);
165		}
166	}
167	switch (func) {
168	case F_GET:
169		if (aflag) {
170			if (argc != 0)
171				usage();
172			search(0, print_entry);
173		} else {
174			if (argc != 1)
175				usage();
176			rtn = get(argv[0]);
177		}
178		break;
179	case F_SET:
180	case F_REPLACE:
181		if (argc < 2 || argc > 6)
182			usage();
183		if (func == F_REPLACE)
184			(void)delete(argv[0]);
185		rtn = set(argc, argv) ? 1 : 0;
186		break;
187	case F_DELETE:
188		if (aflag) {
189			if (argc != 0)
190				usage();
191			search(0, nuke_entry);
192		} else {
193			if (argc != 1)
194				usage();
195			rtn = delete(argv[0]);
196		}
197		break;
198	case F_FILESET:
199		if (argc != 1)
200			usage();
201		rtn = file(argv[0]);
202		break;
203	}
204
205	if (ifnameindex != NULL)
206		if_freenameindex(ifnameindex);
207
208	return (rtn);
209}
210
211/*
212 * Process a file to set standard arp entries
213 */
214static int
215file(char *name)
216{
217	FILE *fp;
218	int i, retval;
219	char line[100], arg[5][50], *args[5], *p;
220
221	if ((fp = fopen(name, "r")) == NULL)
222		err(1, "cannot open %s", name);
223	args[0] = &arg[0][0];
224	args[1] = &arg[1][0];
225	args[2] = &arg[2][0];
226	args[3] = &arg[3][0];
227	args[4] = &arg[4][0];
228	retval = 0;
229	while(fgets(line, sizeof(line), fp) != NULL) {
230		if ((p = strchr(line, '#')) != NULL)
231			*p = '\0';
232		for (p = line; isblank(*p); p++);
233		if (*p == '\n' || *p == '\0')
234			continue;
235		i = sscanf(p, "%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/*
250 * Given a hostname, fills up a (static) struct sockaddr_in with
251 * the address of the host and returns a pointer to the
252 * structure.
253 */
254static struct sockaddr_in *
255getaddr(char *host)
256{
257	struct hostent *hp;
258	static struct sockaddr_in reply;
259
260	bzero(&reply, sizeof(reply));
261	reply.sin_len = sizeof(reply);
262	reply.sin_family = AF_INET;
263	reply.sin_addr.s_addr = inet_addr(host);
264	if (reply.sin_addr.s_addr == INADDR_NONE) {
265		if (!(hp = gethostbyname(host))) {
266			warnx("%s: %s", host, hstrerror(h_errno));
267			return (NULL);
268		}
269		bcopy((char *)hp->h_addr, (char *)&reply.sin_addr,
270			sizeof reply.sin_addr);
271	}
272	return (&reply);
273}
274
275/*
276 * Returns true if the type is a valid one for ARP.
277 */
278static int
279valid_type(int type)
280{
281
282	switch (type) {
283	case IFT_ETHER:
284	case IFT_FDDI:
285	case IFT_ISO88023:
286	case IFT_ISO88024:
287	case IFT_ISO88025:
288	case IFT_L2VLAN:
289	case IFT_BRIDGE:
290		return (1);
291	default:
292		return (0);
293	}
294}
295
296/*
297 * Set an individual arp entry
298 */
299static int
300set(int argc, char **argv)
301{
302	struct sockaddr_in *addr;
303	struct sockaddr_in *dst;	/* what are we looking for */
304	struct sockaddr_dl *sdl;
305	struct rt_msghdr *rtm;
306	struct ether_addr *ea;
307	char *host = argv[0], *eaddr = argv[1];
308	struct sockaddr_dl sdl_m;
309
310	argc -= 2;
311	argv += 2;
312
313	bzero(&sdl_m, sizeof(sdl_m));
314	sdl_m.sdl_len = sizeof(sdl_m);
315	sdl_m.sdl_family = AF_LINK;
316
317	dst = getaddr(host);
318	if (dst == NULL)
319		return (1);
320	doing_proxy = flags = expire_time = 0;
321	while (argc-- > 0) {
322		if (strncmp(argv[0], "temp", 4) == 0) {
323			struct timespec tp;
324			int max_age;
325			size_t len = sizeof(max_age);
326
327			clock_gettime(CLOCK_MONOTONIC, &tp);
328			if (sysctlbyname("net.link.ether.inet.max_age",
329			    &max_age, &len, NULL, 0) != 0)
330				err(1, "sysctlbyname");
331			expire_time = tp.tv_sec + max_age;
332		} else if (strncmp(argv[0], "pub", 3) == 0) {
333			flags |= RTF_ANNOUNCE;
334			doing_proxy = 1;
335			if (argc && strncmp(argv[1], "only", 3) == 0) {
336				/*
337				 * Compatibility: in pre FreeBSD 8 times
338				 * the "only" keyword used to mean that
339				 * an ARP entry should be announced, but
340				 * not installed into routing table.
341				 */
342				argc--; argv++;
343			}
344		} else if (strncmp(argv[0], "blackhole", 9) == 0) {
345			if (flags & RTF_REJECT) {
346				printf("Choose one of blackhole or reject, not both.\n");
347			}
348			flags |= RTF_BLACKHOLE;
349		} else if (strncmp(argv[0], "reject", 6) == 0) {
350			if (flags & RTF_BLACKHOLE) {
351				printf("Choose one of blackhole or reject, not both.\n");
352			}
353			flags |= RTF_REJECT;
354		} else if (strncmp(argv[0], "trail", 5) == 0) {
355			/* XXX deprecated and undocumented feature */
356			printf("%s: Sending trailers is no longer supported\n",
357				host);
358		}
359		argv++;
360	}
361	ea = (struct ether_addr *)LLADDR(&sdl_m);
362	if (doing_proxy && !strcmp(eaddr, "auto")) {
363		if (!get_ether_addr(dst->sin_addr.s_addr, ea)) {
364			printf("no interface found for %s\n",
365			       inet_ntoa(dst->sin_addr));
366			return (1);
367		}
368		sdl_m.sdl_alen = ETHER_ADDR_LEN;
369	} else {
370		struct ether_addr *ea1 = ether_aton(eaddr);
371
372		if (ea1 == NULL) {
373			warnx("invalid Ethernet address '%s'", eaddr);
374			return (1);
375		} else {
376			*ea = *ea1;
377			sdl_m.sdl_alen = ETHER_ADDR_LEN;
378		}
379	}
380
381	/*
382	 * In the case a proxy-arp entry is being added for
383	 * a remote end point, the RTF_ANNOUNCE flag in the
384	 * RTM_GET command is an indication to the kernel
385	 * routing code that the interface associated with
386	 * the prefix route covering the local end of the
387	 * PPP link should be returned, on which ARP applies.
388	 */
389	rtm = rtmsg(RTM_GET, dst, &sdl_m);
390	if (rtm == NULL) {
391		warn("%s", host);
392		return (1);
393	}
394	addr = (struct sockaddr_in *)(rtm + 1);
395	sdl = (struct sockaddr_dl *)(SA_SIZE(addr) + (char *)addr);
396
397	if ((sdl->sdl_family != AF_LINK) ||
398	    (rtm->rtm_flags & RTF_GATEWAY) ||
399	    !valid_type(sdl->sdl_type)) {
400		printf("cannot intuit interface index and type for %s\n", host);
401		return (1);
402	}
403	sdl_m.sdl_type = sdl->sdl_type;
404	sdl_m.sdl_index = sdl->sdl_index;
405	return (rtmsg(RTM_ADD, dst, &sdl_m) == NULL);
406}
407
408/*
409 * Display an individual arp entry
410 */
411static int
412get(char *host)
413{
414	struct sockaddr_in *addr;
415
416	addr = getaddr(host);
417	if (addr == NULL)
418		return (1);
419	if (0 == search(addr->sin_addr.s_addr, print_entry)) {
420		printf("%s (%s) -- no entry",
421		    host, inet_ntoa(addr->sin_addr));
422		if (rifname)
423			printf(" on %s", rifname);
424		printf("\n");
425		return (1);
426	}
427	return (0);
428}
429
430/*
431 * Delete an arp entry
432 */
433static int
434delete(char *host)
435{
436	struct sockaddr_in *addr, *dst;
437	struct rt_msghdr *rtm;
438	struct sockaddr_dl *sdl;
439	struct sockaddr_dl sdl_m;
440
441	dst = getaddr(host);
442	if (dst == NULL)
443		return (1);
444
445	/*
446	 * Perform a regular entry delete first.
447	 */
448	flags &= ~RTF_ANNOUNCE;
449
450	/*
451	 * setup the data structure to notify the kernel
452	 * it is the ARP entry the RTM_GET is interested
453	 * in
454	 */
455	bzero(&sdl_m, sizeof(sdl_m));
456	sdl_m.sdl_len = sizeof(sdl_m);
457	sdl_m.sdl_family = AF_LINK;
458
459	for (;;) {	/* try twice */
460		rtm = rtmsg(RTM_GET, dst, &sdl_m);
461		if (rtm == NULL) {
462			warn("%s", host);
463			return (1);
464		}
465		addr = (struct sockaddr_in *)(rtm + 1);
466		sdl = (struct sockaddr_dl *)(SA_SIZE(addr) + (char *)addr);
467
468		/*
469		 * With the new L2/L3 restructure, the route
470		 * returned is a prefix route. The important
471		 * piece of information from the previous
472		 * RTM_GET is the interface index. In the
473		 * case of ECMP, the kernel will traverse
474		 * the route group for the given entry.
475		 */
476		if (sdl->sdl_family == AF_LINK &&
477		    !(rtm->rtm_flags & RTF_GATEWAY) &&
478		    valid_type(sdl->sdl_type) ) {
479			addr->sin_addr.s_addr = dst->sin_addr.s_addr;
480			break;
481		}
482
483		/*
484		 * Regualar entry delete failed, now check if there
485		 * is a proxy-arp entry to remove.
486		 */
487		if (flags & RTF_ANNOUNCE) {
488			fprintf(stderr, "delete: cannot locate %s\n",host);
489			return (1);
490		}
491
492		flags |= RTF_ANNOUNCE;
493	}
494	rtm->rtm_flags |= RTF_LLDATA;
495	if (rtmsg(RTM_DELETE, dst, NULL) != NULL) {
496		printf("%s (%s) deleted\n", host, inet_ntoa(addr->sin_addr));
497		return (0);
498	}
499	return (1);
500}
501
502
503/*
504 * Search the arp table and do some action on matching entries
505 */
506static int
507search(u_long addr, action_fn *action)
508{
509	int mib[6];
510	size_t needed;
511	char *lim, *buf, *next;
512	struct rt_msghdr *rtm;
513	struct sockaddr_in *sin2;
514	struct sockaddr_dl *sdl;
515	char ifname[IF_NAMESIZE];
516	int st, found_entry = 0;
517
518	mib[0] = CTL_NET;
519	mib[1] = PF_ROUTE;
520	mib[2] = 0;
521	mib[3] = AF_INET;
522	mib[4] = NET_RT_FLAGS;
523#ifdef RTF_LLINFO
524	mib[5] = RTF_LLINFO;
525#else
526	mib[5] = 0;
527#endif
528	if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
529		err(1, "route-sysctl-estimate");
530	if (needed == 0)	/* empty table */
531		return 0;
532	buf = NULL;
533	for (;;) {
534		buf = reallocf(buf, needed);
535		if (buf == NULL)
536			errx(1, "could not reallocate memory");
537		st = sysctl(mib, 6, buf, &needed, NULL, 0);
538		if (st == 0 || errno != ENOMEM)
539			break;
540		needed += needed / 8;
541	}
542	if (st == -1)
543		err(1, "actual retrieval of routing table");
544	lim = buf + needed;
545	for (next = buf; next < lim; next += rtm->rtm_msglen) {
546		rtm = (struct rt_msghdr *)next;
547		sin2 = (struct sockaddr_in *)(rtm + 1);
548		sdl = (struct sockaddr_dl *)((char *)sin2 + SA_SIZE(sin2));
549		if (rifname && if_indextoname(sdl->sdl_index, ifname) &&
550		    strcmp(ifname, rifname))
551			continue;
552		if (addr) {
553			if (addr != sin2->sin_addr.s_addr)
554				continue;
555			found_entry = 1;
556		}
557		(*action)(sdl, sin2, rtm);
558	}
559	free(buf);
560	return (found_entry);
561}
562
563/*
564 * Display an arp entry
565 */
566
567static void
568print_entry(struct sockaddr_dl *sdl,
569	struct sockaddr_in *addr, struct rt_msghdr *rtm)
570{
571	const char *host;
572	struct hostent *hp;
573	struct iso88025_sockaddr_dl_data *trld;
574	struct if_nameindex *p;
575	int seg;
576
577	if (ifnameindex == NULL)
578		if ((ifnameindex = if_nameindex()) == NULL)
579			err(1, "cannot retrieve interface names");
580
581	if (nflag == 0)
582		hp = gethostbyaddr((caddr_t)&(addr->sin_addr),
583		    sizeof addr->sin_addr, AF_INET);
584	else
585		hp = 0;
586	if (hp)
587		host = hp->h_name;
588	else {
589		host = "?";
590		if (h_errno == TRY_AGAIN)
591			nflag = 1;
592	}
593	printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
594	if (sdl->sdl_alen) {
595		if ((sdl->sdl_type == IFT_ETHER ||
596		    sdl->sdl_type == IFT_L2VLAN ||
597		    sdl->sdl_type == IFT_BRIDGE) &&
598		    sdl->sdl_alen == ETHER_ADDR_LEN)
599			printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
600		else {
601			int n = sdl->sdl_nlen > 0 ? sdl->sdl_nlen + 1 : 0;
602
603			printf("%s", link_ntoa(sdl) + n);
604		}
605	} else
606		printf("(incomplete)");
607
608	for (p = ifnameindex; p && ifnameindex->if_index &&
609		 ifnameindex->if_name; p++) {
610		if (p->if_index == sdl->sdl_index) {
611			printf(" on %s", p->if_name);
612			break;
613		}
614	}
615
616	if (rtm->rtm_rmx.rmx_expire == 0)
617		printf(" permanent");
618	else {
619		static struct timespec tp;
620		if (tp.tv_sec == 0)
621			clock_gettime(CLOCK_MONOTONIC, &tp);
622		if ((expire_time = rtm->rtm_rmx.rmx_expire - tp.tv_sec) > 0)
623			printf(" expires in %d seconds", (int)expire_time);
624		else
625			printf(" expired");
626	}
627	if (rtm->rtm_flags & RTF_ANNOUNCE)
628		printf(" published");
629	switch(sdl->sdl_type) {
630	case IFT_ETHER:
631                printf(" [ethernet]");
632                break;
633	case IFT_ISO88025:
634                printf(" [token-ring]");
635		trld = SDL_ISO88025(sdl);
636		if (trld->trld_rcf != 0) {
637			printf(" rt=%x", ntohs(trld->trld_rcf));
638			for (seg = 0;
639			     seg < ((TR_RCF_RIFLEN(trld->trld_rcf) - 2 ) / 2);
640			     seg++)
641				printf(":%x", ntohs(*(trld->trld_route[seg])));
642		}
643                break;
644	case IFT_FDDI:
645                printf(" [fddi]");
646                break;
647	case IFT_ATM:
648                printf(" [atm]");
649                break;
650	case IFT_L2VLAN:
651		printf(" [vlan]");
652		break;
653	case IFT_IEEE1394:
654                printf(" [firewire]");
655                break;
656	case IFT_BRIDGE:
657		printf(" [bridge]");
658		break;
659	default:
660		break;
661        }
662
663	printf("\n");
664
665}
666
667/*
668 * Nuke an arp entry
669 */
670static void
671nuke_entry(struct sockaddr_dl *sdl __unused,
672	struct sockaddr_in *addr, struct rt_msghdr *rtm __unused)
673{
674	char ip[20];
675
676	snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
677	delete(ip);
678}
679
680static void
681usage(void)
682{
683	fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
684		"usage: arp [-n] [-i interface] hostname",
685		"       arp [-n] [-i interface] -a",
686		"       arp -d hostname [pub]",
687		"       arp -d [-i interface] -a",
688		"       arp -s hostname ether_addr [temp] [reject | blackhole] [pub [only]]",
689		"       arp -S hostname ether_addr [temp] [reject | blackhole] [pub [only]]",
690		"       arp -f filename");
691	exit(1);
692}
693
694static struct rt_msghdr *
695rtmsg(int cmd, struct sockaddr_in *dst, struct sockaddr_dl *sdl)
696{
697	static int seq;
698	int rlen;
699	int l;
700	struct sockaddr_in so_mask, *som = &so_mask;
701	static int s = -1;
702	static pid_t pid;
703
704	static struct	{
705		struct	rt_msghdr m_rtm;
706		char	m_space[512];
707	}	m_rtmsg;
708
709	struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
710	char *cp = m_rtmsg.m_space;
711
712	if (s < 0) {	/* first time: open socket, get pid */
713		s = socket(PF_ROUTE, SOCK_RAW, 0);
714		if (s < 0)
715			err(1, "socket");
716		pid = getpid();
717	}
718	bzero(&so_mask, sizeof(so_mask));
719	so_mask.sin_len = 8;
720	so_mask.sin_addr.s_addr = 0xffffffff;
721
722	errno = 0;
723	/*
724	 * XXX RTM_DELETE relies on a previous RTM_GET to fill the buffer
725	 * appropriately.
726	 */
727	if (cmd == RTM_DELETE)
728		goto doit;
729	bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
730	rtm->rtm_flags = flags;
731	rtm->rtm_version = RTM_VERSION;
732
733	switch (cmd) {
734	default:
735		errx(1, "internal wrong cmd");
736	case RTM_ADD:
737		rtm->rtm_addrs |= RTA_GATEWAY;
738		rtm->rtm_rmx.rmx_expire = expire_time;
739		rtm->rtm_inits = RTV_EXPIRE;
740		rtm->rtm_flags |= (RTF_HOST | RTF_STATIC | RTF_LLDATA);
741		if (doing_proxy) {
742			rtm->rtm_addrs |= RTA_NETMASK;
743			rtm->rtm_flags &= ~RTF_HOST;
744		}
745		/* FALLTHROUGH */
746	case RTM_GET:
747		rtm->rtm_addrs |= RTA_DST;
748	}
749#define NEXTADDR(w, s)					   \
750	do {						   \
751		if ((s) != NULL && rtm->rtm_addrs & (w)) { \
752			bcopy((s), cp, sizeof(*(s)));	   \
753			cp += SA_SIZE(s);		   \
754		}					   \
755	} while (0)
756
757	NEXTADDR(RTA_DST, dst);
758	NEXTADDR(RTA_GATEWAY, sdl);
759	NEXTADDR(RTA_NETMASK, som);
760
761	rtm->rtm_msglen = cp - (char *)&m_rtmsg;
762doit:
763	l = rtm->rtm_msglen;
764	rtm->rtm_seq = ++seq;
765	rtm->rtm_type = cmd;
766	if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
767		if (errno != ESRCH || cmd != RTM_DELETE) {
768			warn("writing to routing socket");
769			return (NULL);
770		}
771	}
772	do {
773		l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
774	} while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
775	if (l < 0)
776		warn("read from routing socket");
777	return (rtm);
778}
779
780/*
781 * get_ether_addr - get the hardware address of an interface on the
782 * the same subnet as ipaddr.
783 */
784#define MAX_IFS		32
785
786static int
787get_ether_addr(in_addr_t ipaddr, struct ether_addr *hwaddr)
788{
789	struct ifreq *ifr, *ifend, *ifp;
790	in_addr_t ina, mask;
791	struct sockaddr_dl *dla;
792	struct ifreq ifreq;
793	struct ifconf ifc;
794	struct ifreq ifs[MAX_IFS];
795	int sock;
796	int retval = 0;
797
798	sock = socket(AF_INET, SOCK_DGRAM, 0);
799	if (sock < 0)
800		err(1, "socket");
801
802	ifc.ifc_len = sizeof(ifs);
803	ifc.ifc_req = ifs;
804	if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
805		warnx("ioctl(SIOCGIFCONF)");
806		goto done;
807	}
808
809#define NEXTIFR(i)						\
810    ((struct ifreq *)((char *)&(i)->ifr_addr			\
811	+ MAX((i)->ifr_addr.sa_len, sizeof((i)->ifr_addr))) )
812
813	/*
814	 * Scan through looking for an interface with an Internet
815	 * address on the same subnet as `ipaddr'.
816	 */
817	ifend = (struct ifreq *)(ifc.ifc_buf + ifc.ifc_len);
818	for (ifr = ifc.ifc_req; ifr < ifend; ifr = NEXTIFR(ifr) ) {
819		if (ifr->ifr_addr.sa_family != AF_INET)
820			continue;
821		strncpy(ifreq.ifr_name, ifr->ifr_name,
822			sizeof(ifreq.ifr_name));
823		ifreq.ifr_addr = ifr->ifr_addr;
824		/*
825		 * Check that the interface is up,
826		 * and not point-to-point or loopback.
827		 */
828		if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
829			continue;
830		if ((ifreq.ifr_flags &
831		     (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
832				IFF_LOOPBACK|IFF_NOARP))
833		     != (IFF_UP|IFF_BROADCAST))
834			continue;
835		/*
836		 * Get its netmask and check that it's on
837		 * the right subnet.
838		 */
839		if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
840			continue;
841		mask = ((struct sockaddr_in *)
842			&ifreq.ifr_addr)->sin_addr.s_addr;
843		ina = ((struct sockaddr_in *)
844			&ifr->ifr_addr)->sin_addr.s_addr;
845		if ((ipaddr & mask) == (ina & mask))
846			break; /* ok, we got it! */
847	}
848
849	if (ifr >= ifend)
850		goto done;
851
852	/*
853	 * Now scan through again looking for a link-level address
854	 * for this interface.
855	 */
856	ifp = ifr;
857	for (ifr = ifc.ifc_req; ifr < ifend; ifr = NEXTIFR(ifr))
858		if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0 &&
859		    ifr->ifr_addr.sa_family == AF_LINK)
860			break;
861	if (ifr >= ifend)
862		goto done;
863	/*
864	 * Found the link-level address - copy it out
865	 */
866	dla = (struct sockaddr_dl *) &ifr->ifr_addr;
867	memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
868	printf("using interface %s for proxy with address ",
869		ifp->ifr_name);
870	printf("%s\n", ether_ntoa(hwaddr));
871	retval = dla->sdl_alen;
872done:
873	close(sock);
874	return (retval);
875}
876