arp.c revision 246143 
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: head/usr.sbin/arp/arp.c 246143 2013-01-31 08:55:21Z glebius $");
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			rtn = delete(argv[0]);
192		break;
193	case F_FILESET:
194		if (argc != 1)
195			usage();
196		rtn = file(argv[0]);
197		break;
198	}
199
200	return (rtn);
201}
202
203/*
204 * Process a file to set standard arp entries
205 */
206static int
207file(char *name)
208{
209	FILE *fp;
210	int i, retval;
211	char line[100], arg[5][50], *args[5], *p;
212
213	if ((fp = fopen(name, "r")) == NULL)
214		err(1, "cannot open %s", name);
215	args[0] = &arg[0][0];
216	args[1] = &arg[1][0];
217	args[2] = &arg[2][0];
218	args[3] = &arg[3][0];
219	args[4] = &arg[4][0];
220	retval = 0;
221	while(fgets(line, sizeof(line), fp) != NULL) {
222		if ((p = strchr(line, '#')) != NULL)
223			*p = '\0';
224		for (p = line; isblank(*p); p++);
225		if (*p == '\n' || *p == '\0')
226			continue;
227		i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1],
228		    arg[2], arg[3], arg[4]);
229		if (i < 2) {
230			warnx("bad line: %s", line);
231			retval = 1;
232			continue;
233		}
234		if (set(i, args))
235			retval = 1;
236	}
237	fclose(fp);
238	return (retval);
239}
240
241/*
242 * Given a hostname, fills up a (static) struct sockaddr_in with
243 * the address of the host and returns a pointer to the
244 * structure.
245 */
246static struct sockaddr_in *
247getaddr(char *host)
248{
249	struct hostent *hp;
250	static struct sockaddr_in reply;
251
252	bzero(&reply, sizeof(reply));
253	reply.sin_len = sizeof(reply);
254	reply.sin_family = AF_INET;
255	reply.sin_addr.s_addr = inet_addr(host);
256	if (reply.sin_addr.s_addr == INADDR_NONE) {
257		if (!(hp = gethostbyname(host))) {
258			warnx("%s: %s", host, hstrerror(h_errno));
259			return (NULL);
260		}
261		bcopy((char *)hp->h_addr, (char *)&reply.sin_addr,
262			sizeof reply.sin_addr);
263	}
264	return (&reply);
265}
266
267/*
268 * Returns true if the type is a valid one for ARP.
269 */
270static int
271valid_type(int type)
272{
273
274	switch (type) {
275	case IFT_ETHER:
276	case IFT_FDDI:
277	case IFT_ISO88023:
278	case IFT_ISO88024:
279	case IFT_ISO88025:
280	case IFT_L2VLAN:
281	case IFT_BRIDGE:
282		return (1);
283	default:
284		return (0);
285	}
286}
287
288/*
289 * Set an individual arp entry
290 */
291static int
292set(int argc, char **argv)
293{
294	struct sockaddr_in *addr;
295	struct sockaddr_in *dst;	/* what are we looking for */
296	struct sockaddr_dl *sdl;
297	struct rt_msghdr *rtm;
298	struct ether_addr *ea;
299	char *host = argv[0], *eaddr = argv[1];
300	struct sockaddr_dl sdl_m;
301
302	argc -= 2;
303	argv += 2;
304
305	bzero(&sdl_m, sizeof(sdl_m));
306	sdl_m.sdl_len = sizeof(sdl_m);
307	sdl_m.sdl_family = AF_LINK;
308
309	dst = getaddr(host);
310	if (dst == NULL)
311		return (1);
312	doing_proxy = flags = expire_time = 0;
313	while (argc-- > 0) {
314		if (strncmp(argv[0], "temp", 4) == 0) {
315			struct timespec tp;
316			int max_age;
317			size_t len = sizeof(max_age);
318
319			clock_gettime(CLOCK_MONOTONIC, &tp);
320			if (sysctlbyname("net.link.ether.inet.max_age",
321			    &max_age, &len, NULL, 0) != 0)
322				err(1, "sysctlbyname");
323			expire_time = tp.tv_sec + max_age;
324		} else if (strncmp(argv[0], "pub", 3) == 0) {
325			flags |= RTF_ANNOUNCE;
326			doing_proxy = 1;
327			if (argc && strncmp(argv[1], "only", 3) == 0) {
328				/*
329				 * Compatibility: in pre FreeBSD 8 times
330				 * the "only" keyword used to mean that
331				 * an ARP entry should be announced, but
332				 * not installed into routing table.
333				 */
334				argc--; argv++;
335			}
336		} else if (strncmp(argv[0], "blackhole", 9) == 0) {
337			if (flags & RTF_REJECT) {
338				printf("Choose one of blackhole or reject, not both.\n");
339			}
340			flags |= RTF_BLACKHOLE;
341		} else if (strncmp(argv[0], "reject", 6) == 0) {
342			if (flags & RTF_BLACKHOLE) {
343				printf("Choose one of blackhole or reject, not both.\n");
344			}
345			flags |= RTF_REJECT;
346		} else if (strncmp(argv[0], "trail", 5) == 0) {
347			/* XXX deprecated and undocumented feature */
348			printf("%s: Sending trailers is no longer supported\n",
349				host);
350		}
351		argv++;
352	}
353	ea = (struct ether_addr *)LLADDR(&sdl_m);
354	if (doing_proxy && !strcmp(eaddr, "auto")) {
355		if (!get_ether_addr(dst->sin_addr.s_addr, ea)) {
356			printf("no interface found for %s\n",
357			       inet_ntoa(dst->sin_addr));
358			return (1);
359		}
360		sdl_m.sdl_alen = ETHER_ADDR_LEN;
361	} else {
362		struct ether_addr *ea1 = ether_aton(eaddr);
363
364		if (ea1 == NULL) {
365			warnx("invalid Ethernet address '%s'", eaddr);
366			return (1);
367		} else {
368			*ea = *ea1;
369			sdl_m.sdl_alen = ETHER_ADDR_LEN;
370		}
371	}
372
373	/*
374	 * In the case a proxy-arp entry is being added for
375	 * a remote end point, the RTF_ANNOUNCE flag in the
376	 * RTM_GET command is an indication to the kernel
377	 * routing code that the interface associated with
378	 * the prefix route covering the local end of the
379	 * PPP link should be returned, on which ARP applies.
380	 */
381	rtm = rtmsg(RTM_GET, dst, &sdl_m);
382	if (rtm == NULL) {
383		warn("%s", host);
384		return (1);
385	}
386	addr = (struct sockaddr_in *)(rtm + 1);
387	sdl = (struct sockaddr_dl *)(SA_SIZE(addr) + (char *)addr);
388
389	if ((sdl->sdl_family != AF_LINK) ||
390	    (rtm->rtm_flags & RTF_GATEWAY) ||
391	    !valid_type(sdl->sdl_type)) {
392		printf("cannot intuit interface index and type for %s\n", host);
393		return (1);
394	}
395	sdl_m.sdl_type = sdl->sdl_type;
396	sdl_m.sdl_index = sdl->sdl_index;
397	return (rtmsg(RTM_ADD, dst, &sdl_m) == NULL);
398}
399
400/*
401 * Display an individual arp entry
402 */
403static int
404get(char *host)
405{
406	struct sockaddr_in *addr;
407
408	addr = getaddr(host);
409	if (addr == NULL)
410		return (1);
411	if (0 == search(addr->sin_addr.s_addr, print_entry)) {
412		printf("%s (%s) -- no entry",
413		    host, inet_ntoa(addr->sin_addr));
414		if (rifname)
415			printf(" on %s", rifname);
416		printf("\n");
417		return (1);
418	}
419	return (0);
420}
421
422/*
423 * Delete an arp entry
424 */
425static int
426delete(char *host)
427{
428	struct sockaddr_in *addr, *dst;
429	struct rt_msghdr *rtm;
430	struct sockaddr_dl *sdl;
431	struct sockaddr_dl sdl_m;
432
433	dst = getaddr(host);
434	if (dst == NULL)
435		return (1);
436
437	/*
438	 * Perform a regular entry delete first.
439	 */
440	flags &= ~RTF_ANNOUNCE;
441
442	/*
443	 * setup the data structure to notify the kernel
444	 * it is the ARP entry the RTM_GET is interested
445	 * in
446	 */
447	bzero(&sdl_m, sizeof(sdl_m));
448	sdl_m.sdl_len = sizeof(sdl_m);
449	sdl_m.sdl_family = AF_LINK;
450
451	for (;;) {	/* try twice */
452		rtm = rtmsg(RTM_GET, dst, &sdl_m);
453		if (rtm == NULL) {
454			warn("%s", host);
455			return (1);
456		}
457		addr = (struct sockaddr_in *)(rtm + 1);
458		sdl = (struct sockaddr_dl *)(SA_SIZE(addr) + (char *)addr);
459
460		/*
461		 * With the new L2/L3 restructure, the route
462		 * returned is a prefix route. The important
463		 * piece of information from the previous
464		 * RTM_GET is the interface index. In the
465		 * case of ECMP, the kernel will traverse
466		 * the route group for the given entry.
467		 */
468		if (sdl->sdl_family == AF_LINK &&
469		    !(rtm->rtm_flags & RTF_GATEWAY) &&
470		    valid_type(sdl->sdl_type) ) {
471			addr->sin_addr.s_addr = dst->sin_addr.s_addr;
472			break;
473		}
474
475		/*
476		 * Regualar entry delete failed, now check if there
477		 * is a proxy-arp entry to remove.
478		 */
479		if (flags & RTF_ANNOUNCE) {
480			fprintf(stderr, "delete: cannot locate %s\n",host);
481			return (1);
482		}
483
484		flags |= RTF_ANNOUNCE;
485	}
486	rtm->rtm_flags |= RTF_LLDATA;
487	if (rtmsg(RTM_DELETE, dst, NULL) != NULL) {
488		printf("%s (%s) deleted\n", host, inet_ntoa(addr->sin_addr));
489		return (0);
490	}
491	return (1);
492}
493
494
495/*
496 * Search the arp table and do some action on matching entries
497 */
498static int
499search(u_long addr, action_fn *action)
500{
501	int mib[6];
502	size_t needed;
503	char *lim, *buf, *next;
504	struct rt_msghdr *rtm;
505	struct sockaddr_in *sin2;
506	struct sockaddr_dl *sdl;
507	char ifname[IF_NAMESIZE];
508	int st, found_entry = 0;
509
510	mib[0] = CTL_NET;
511	mib[1] = PF_ROUTE;
512	mib[2] = 0;
513	mib[3] = AF_INET;
514	mib[4] = NET_RT_FLAGS;
515#ifdef RTF_LLINFO
516	mib[5] = RTF_LLINFO;
517#else
518	mib[5] = 0;
519#endif
520	if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
521		err(1, "route-sysctl-estimate");
522	if (needed == 0)	/* empty table */
523		return 0;
524	buf = NULL;
525	for (;;) {
526		buf = reallocf(buf, needed);
527		if (buf == NULL)
528			errx(1, "could not reallocate memory");
529		st = sysctl(mib, 6, buf, &needed, NULL, 0);
530		if (st == 0 || errno != ENOMEM)
531			break;
532		needed += needed / 8;
533	}
534	if (st == -1)
535		err(1, "actual retrieval of routing table");
536	lim = buf + needed;
537	for (next = buf; next < lim; next += rtm->rtm_msglen) {
538		rtm = (struct rt_msghdr *)next;
539		sin2 = (struct sockaddr_in *)(rtm + 1);
540		sdl = (struct sockaddr_dl *)((char *)sin2 + SA_SIZE(sin2));
541		if (rifname && if_indextoname(sdl->sdl_index, ifname) &&
542		    strcmp(ifname, rifname))
543			continue;
544		if (addr) {
545			if (addr != sin2->sin_addr.s_addr)
546				continue;
547			found_entry = 1;
548		}
549		(*action)(sdl, sin2, rtm);
550	}
551	free(buf);
552	return (found_entry);
553}
554
555/*
556 * Display an arp entry
557 */
558static char lifname[IF_NAMESIZE];
559static int64_t lifindex = -1;
560
561static void
562print_entry(struct sockaddr_dl *sdl,
563	struct sockaddr_in *addr, struct rt_msghdr *rtm)
564{
565	const char *host;
566	struct hostent *hp;
567	struct iso88025_sockaddr_dl_data *trld;
568	int seg;
569
570	if (nflag == 0)
571		hp = gethostbyaddr((caddr_t)&(addr->sin_addr),
572		    sizeof addr->sin_addr, AF_INET);
573	else
574		hp = 0;
575	if (hp)
576		host = hp->h_name;
577	else {
578		host = "?";
579		if (h_errno == TRY_AGAIN)
580			nflag = 1;
581	}
582	printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
583	if (sdl->sdl_alen) {
584		if ((sdl->sdl_type == IFT_ETHER ||
585		    sdl->sdl_type == IFT_L2VLAN ||
586		    sdl->sdl_type == IFT_BRIDGE) &&
587		    sdl->sdl_alen == ETHER_ADDR_LEN)
588			printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
589		else {
590			int n = sdl->sdl_nlen > 0 ? sdl->sdl_nlen + 1 : 0;
591
592			printf("%s", link_ntoa(sdl) + n);
593		}
594	} else
595		printf("(incomplete)");
596	if (sdl->sdl_index != lifindex &&
597	    if_indextoname(sdl->sdl_index, lifname) != NULL) {
598        	lifindex = sdl->sdl_index;
599		printf(" on %s", lifname);
600        } else if (sdl->sdl_index == lifindex)
601		printf(" on %s", lifname);
602	if (rtm->rtm_rmx.rmx_expire == 0)
603		printf(" permanent");
604	else {
605		static struct timespec tp;
606		if (tp.tv_sec == 0)
607			clock_gettime(CLOCK_MONOTONIC, &tp);
608		if ((expire_time = rtm->rtm_rmx.rmx_expire - tp.tv_sec) > 0)
609			printf(" expires in %d seconds", (int)expire_time);
610		else
611			printf(" expired");
612	}
613	if (rtm->rtm_flags & RTF_ANNOUNCE)
614		printf(" published");
615	switch(sdl->sdl_type) {
616	case IFT_ETHER:
617                printf(" [ethernet]");
618                break;
619	case IFT_ISO88025:
620                printf(" [token-ring]");
621		trld = SDL_ISO88025(sdl);
622		if (trld->trld_rcf != 0) {
623			printf(" rt=%x", ntohs(trld->trld_rcf));
624			for (seg = 0;
625			     seg < ((TR_RCF_RIFLEN(trld->trld_rcf) - 2 ) / 2);
626			     seg++)
627				printf(":%x", ntohs(*(trld->trld_route[seg])));
628		}
629                break;
630	case IFT_FDDI:
631                printf(" [fddi]");
632                break;
633	case IFT_ATM:
634                printf(" [atm]");
635                break;
636	case IFT_L2VLAN:
637		printf(" [vlan]");
638		break;
639	case IFT_IEEE1394:
640                printf(" [firewire]");
641                break;
642	case IFT_BRIDGE:
643		printf(" [bridge]");
644		break;
645	default:
646		break;
647        }
648
649	printf("\n");
650
651}
652
653/*
654 * Nuke an arp entry
655 */
656static void
657nuke_entry(struct sockaddr_dl *sdl __unused,
658	struct sockaddr_in *addr, struct rt_msghdr *rtm __unused)
659{
660	char ip[20];
661
662	snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
663	delete(ip);
664}
665
666static void
667usage(void)
668{
669	fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
670		"usage: arp [-n] [-i interface] hostname",
671		"       arp [-n] [-i interface] -a",
672		"       arp -d hostname [pub]",
673		"       arp -d [-i interface] -a",
674		"       arp -s hostname ether_addr [temp] [reject | blackhole] [pub [only]]",
675		"       arp -S hostname ether_addr [temp] [reject | blackhole] [pub [only]]",
676		"       arp -f filename");
677	exit(1);
678}
679
680static struct rt_msghdr *
681rtmsg(int cmd, struct sockaddr_in *dst, struct sockaddr_dl *sdl)
682{
683	static int seq;
684	int rlen;
685	int l;
686	struct sockaddr_in so_mask, *som = &so_mask;
687	static int s = -1;
688	static pid_t pid;
689
690	static struct	{
691		struct	rt_msghdr m_rtm;
692		char	m_space[512];
693	}	m_rtmsg;
694
695	struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
696	char *cp = m_rtmsg.m_space;
697
698	if (s < 0) {	/* first time: open socket, get pid */
699		s = socket(PF_ROUTE, SOCK_RAW, 0);
700		if (s < 0)
701			err(1, "socket");
702		pid = getpid();
703	}
704	bzero(&so_mask, sizeof(so_mask));
705	so_mask.sin_len = 8;
706	so_mask.sin_addr.s_addr = 0xffffffff;
707
708	errno = 0;
709	/*
710	 * XXX RTM_DELETE relies on a previous RTM_GET to fill the buffer
711	 * appropriately.
712	 */
713	if (cmd == RTM_DELETE)
714		goto doit;
715	bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
716	rtm->rtm_flags = flags;
717	rtm->rtm_version = RTM_VERSION;
718
719	switch (cmd) {
720	default:
721		errx(1, "internal wrong cmd");
722	case RTM_ADD:
723		rtm->rtm_addrs |= RTA_GATEWAY;
724		rtm->rtm_rmx.rmx_expire = expire_time;
725		rtm->rtm_inits = RTV_EXPIRE;
726		rtm->rtm_flags |= (RTF_HOST | RTF_STATIC | RTF_LLDATA);
727		if (doing_proxy) {
728			rtm->rtm_addrs |= RTA_NETMASK;
729			rtm->rtm_flags &= ~RTF_HOST;
730		}
731		/* FALLTHROUGH */
732	case RTM_GET:
733		rtm->rtm_addrs |= RTA_DST;
734	}
735#define NEXTADDR(w, s)					   \
736	do {						   \
737		if ((s) != NULL && rtm->rtm_addrs & (w)) { \
738			bcopy((s), cp, sizeof(*(s)));	   \
739			cp += SA_SIZE(s);		   \
740		}					   \
741	} while (0)
742
743	NEXTADDR(RTA_DST, dst);
744	NEXTADDR(RTA_GATEWAY, sdl);
745	NEXTADDR(RTA_NETMASK, som);
746
747	rtm->rtm_msglen = cp - (char *)&m_rtmsg;
748doit:
749	l = rtm->rtm_msglen;
750	rtm->rtm_seq = ++seq;
751	rtm->rtm_type = cmd;
752	if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
753		if (errno != ESRCH || cmd != RTM_DELETE) {
754			warn("writing to routing socket");
755			return (NULL);
756		}
757	}
758	do {
759		l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
760	} while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
761	if (l < 0)
762		warn("read from routing socket");
763	return (rtm);
764}
765
766/*
767 * get_ether_addr - get the hardware address of an interface on the
768 * the same subnet as ipaddr.
769 */
770#define MAX_IFS		32
771
772static int
773get_ether_addr(in_addr_t ipaddr, struct ether_addr *hwaddr)
774{
775	struct ifreq *ifr, *ifend, *ifp;
776	in_addr_t ina, mask;
777	struct sockaddr_dl *dla;
778	struct ifreq ifreq;
779	struct ifconf ifc;
780	struct ifreq ifs[MAX_IFS];
781	int sock;
782	int retval = 0;
783
784	sock = socket(AF_INET, SOCK_DGRAM, 0);
785	if (sock < 0)
786		err(1, "socket");
787
788	ifc.ifc_len = sizeof(ifs);
789	ifc.ifc_req = ifs;
790	if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
791		warnx("ioctl(SIOCGIFCONF)");
792		goto done;
793	}
794
795#define NEXTIFR(i)						\
796    ((struct ifreq *)((char *)&(i)->ifr_addr			\
797	+ MAX((i)->ifr_addr.sa_len, sizeof((i)->ifr_addr))) )
798
799	/*
800	 * Scan through looking for an interface with an Internet
801	 * address on the same subnet as `ipaddr'.
802	 */
803	ifend = (struct ifreq *)(ifc.ifc_buf + ifc.ifc_len);
804	for (ifr = ifc.ifc_req; ifr < ifend; ifr = NEXTIFR(ifr) ) {
805		if (ifr->ifr_addr.sa_family != AF_INET)
806			continue;
807		strncpy(ifreq.ifr_name, ifr->ifr_name,
808			sizeof(ifreq.ifr_name));
809		ifreq.ifr_addr = ifr->ifr_addr;
810		/*
811		 * Check that the interface is up,
812		 * and not point-to-point or loopback.
813		 */
814		if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
815			continue;
816		if ((ifreq.ifr_flags &
817		     (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
818				IFF_LOOPBACK|IFF_NOARP))
819		     != (IFF_UP|IFF_BROADCAST))
820			continue;
821		/*
822		 * Get its netmask and check that it's on
823		 * the right subnet.
824		 */
825		if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
826			continue;
827		mask = ((struct sockaddr_in *)
828			&ifreq.ifr_addr)->sin_addr.s_addr;
829		ina = ((struct sockaddr_in *)
830			&ifr->ifr_addr)->sin_addr.s_addr;
831		if ((ipaddr & mask) == (ina & mask))
832			break; /* ok, we got it! */
833	}
834
835	if (ifr >= ifend)
836		goto done;
837
838	/*
839	 * Now scan through again looking for a link-level address
840	 * for this interface.
841	 */
842	ifp = ifr;
843	for (ifr = ifc.ifc_req; ifr < ifend; ifr = NEXTIFR(ifr))
844		if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0 &&
845		    ifr->ifr_addr.sa_family == AF_LINK)
846			break;
847	if (ifr >= ifend)
848		goto done;
849	/*
850	 * Found the link-level address - copy it out
851	 */
852	dla = (struct sockaddr_dl *) &ifr->ifr_addr;
853	memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
854	printf("using interface %s for proxy with address ",
855		ifp->ifr_name);
856	printf("%s\n", ether_ntoa(hwaddr));
857	retval = dla->sdl_alen;
858done:
859	close(sock);
860	return (retval);
861}
862