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
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
116int
117main(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 */
209static int
210file(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 */
249static struct sockaddr_in *
250getaddr(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 */
273static int
274valid_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 */
294static int
295set(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 */
406static int
407get(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 */
428static int
429delete(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 */
501static int
502search(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 */
561static char lifname[IF_NAMESIZE];
562static int64_t lifindex = -1;
563
564static void
565print_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 */
659static void
660nuke_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
669static void
670usage(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
683static struct rt_msghdr *
684rtmsg(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;
751doit:
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
775static int
776get_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;
861done:
862	close(sock);
863	return (retval);
864}
865