1/*
2 * Copyright (c) 1982, 1986, 1988, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 * @(#)ip_icmp.c 8.2 (Berkeley) 1/4/94
34 * $Id: ip_icmp.c,v 1.15 1995/12/08 16:46:06 wollman Exp $
35 */
36
37#include <sys/param.h>
38#include <sys/systm.h>
39#include <sys/malloc.h>
40#include <sys/mbuf.h>
41#include <sys/protosw.h>
42#include <sys/socket.h>
43#include <sys/time.h>
44#include <sys/kernel.h>
45#include <sys/socket.h>
46#include <sys/sysctl.h>
47
48#include <net/if.h>
49#include <net/route.h>
50
51#include <netinet/in.h>
52#include <netinet/in_systm.h>
53#include <netinet/in_var.h>
54#include <netinet/ip.h>
55#include <netinet/ip_icmp.h>
56#include <netinet/ip_var.h>
57#include <netinet/icmp_var.h>
58
59/*
60 * ICMP routines: error generation, receive packet processing, and
61 * routines to turnaround packets back to the originator, and
62 * host table maintenance routines.
63 */
64
65static struct icmpstat icmpstat;
66SYSCTL_STRUCT(_net_inet_icmp, ICMPCTL_STATS, stats, CTLFLAG_RD,
67 &icmpstat, icmpstat, "");
68
69static int icmpmaskrepl = 0;
70SYSCTL_INT(_net_inet_icmp, ICMPCTL_MASKREPL, maskrepl, CTLFLAG_RW,
71 &icmpmaskrepl, 0, "");
72
73#ifdef ICMPPRINTFS
74int icmpprintfs = 0;
75#endif
76
77static void icmp_reflect __P((struct mbuf *));
78static void icmp_send __P((struct mbuf *, struct mbuf *));
79static int ip_next_mtu __P((int, int));
80
81extern struct protosw inetsw[];
82
83/*
84 * Generate an error packet of type error
85 * in response to bad packet ip.
86 */
87void
88icmp_error(n, type, code, dest, destifp)
89 struct mbuf *n;
90 int type, code;
91 n_long dest;
92 struct ifnet *destifp;
93{
94 register struct ip *oip = mtod(n, struct ip *), *nip;
95 register unsigned oiplen = oip->ip_hl << 2;
96 register struct icmp *icp;
97 register struct mbuf *m;
98 unsigned icmplen;
99
100#ifdef ICMPPRINTFS
101 if (icmpprintfs)
102 printf("icmp_error(%p, %x, %d)\n", oip, type, code);
103#endif
104 if (type != ICMP_REDIRECT)
105 icmpstat.icps_error++;
106 /*
107 * Don't send error if not the first fragment of message.
108 * Don't error if the old packet protocol was ICMP
109 * error message, only known informational types.
110 */
111 if (oip->ip_off &~ (IP_MF|IP_DF))
112 goto freeit;
113 if (oip->ip_p == IPPROTO_ICMP && type != ICMP_REDIRECT &&
114 n->m_len >= oiplen + ICMP_MINLEN &&
115 !ICMP_INFOTYPE(((struct icmp *)((caddr_t)oip + oiplen))->icmp_type)) {
116 icmpstat.icps_oldicmp++;
117 goto freeit;
118 }
119 /* Don't send error in response to a multicast or broadcast packet */
120 if (n->m_flags & (M_BCAST|M_MCAST))
121 goto freeit;
122 /*
123 * First, formulate icmp message
124 */
125 m = m_gethdr(M_DONTWAIT, MT_HEADER);
126 if (m == NULL)
127 goto freeit;
128 icmplen = oiplen + min(8, oip->ip_len);
129 m->m_len = icmplen + ICMP_MINLEN;
130 MH_ALIGN(m, m->m_len);
131 icp = mtod(m, struct icmp *);
132 if ((u_int)type > ICMP_MAXTYPE)
133 panic("icmp_error");
134 icmpstat.icps_outhist[type]++;
135 icp->icmp_type = type;
136 if (type == ICMP_REDIRECT)
137 icp->icmp_gwaddr.s_addr = dest;
138 else {
139 icp->icmp_void = 0;
140 /*
141 * The following assignments assume an overlay with the
142 * zeroed icmp_void field.
143 */
144 if (type == ICMP_PARAMPROB) {
145 icp->icmp_pptr = code;
146 code = 0;
147 } else if (type == ICMP_UNREACH &&
148 code == ICMP_UNREACH_NEEDFRAG && destifp) {
149 icp->icmp_nextmtu = htons(destifp->if_mtu);
150 }
151 }
152
153 icp->icmp_code = code;
154 bcopy((caddr_t)oip, (caddr_t)&icp->icmp_ip, icmplen);
155 nip = &icp->icmp_ip;
156 nip->ip_len = htons((u_short)(nip->ip_len + oiplen));
157
158 /*
159 * Now, copy old ip header (without options)
160 * in front of icmp message.
161 */
162 if (m->m_data - sizeof(struct ip) < m->m_pktdat)
163 panic("icmp len");
164 m->m_data -= sizeof(struct ip);
165 m->m_len += sizeof(struct ip);
166 m->m_pkthdr.len = m->m_len;
167 m->m_pkthdr.rcvif = n->m_pkthdr.rcvif;
168 nip = mtod(m, struct ip *);
169 bcopy((caddr_t)oip, (caddr_t)nip, sizeof(struct ip));
170 nip->ip_len = m->m_len;
171 nip->ip_hl = sizeof(struct ip) >> 2;
172 nip->ip_p = IPPROTO_ICMP;
173 nip->ip_tos = 0;
174 icmp_reflect(m);
175
176freeit:
177 m_freem(n);
178}
179
180static struct sockaddr_in icmpsrc = { sizeof (struct sockaddr_in), AF_INET };
181static struct sockaddr_in icmpdst = { sizeof (struct sockaddr_in), AF_INET };
182static struct sockaddr_in icmpgw = { sizeof (struct sockaddr_in), AF_INET };
183
184/*
185 * Process a received ICMP message.
186 */
187void
188icmp_input(m, hlen)
189 register struct mbuf *m;
190 int hlen;
191{
192 register struct icmp *icp;
193 register struct ip *ip = mtod(m, struct ip *);
194 int icmplen = ip->ip_len;
195 register int i;
196 struct in_ifaddr *ia;
197 void (*ctlfunc) __P((int, struct sockaddr *, caddr_t));
198 int code;
199
200 /*
201 * Locate icmp structure in mbuf, and check
202 * that not corrupted and of at least minimum length.
203 */
204#ifdef ICMPPRINTFS
205 if (icmpprintfs) {
206 char buf[4 * sizeof "123"];
207 strcpy(buf, inet_ntoa(ip->ip_src));
208 printf("icmp_input from %s to %s, len %d\n",
209 buf, inet_ntoa(ip->ip_dst), icmplen);
210 }
211#endif
212 if (icmplen < ICMP_MINLEN) {
213 icmpstat.icps_tooshort++;
214 goto freeit;
215 }
216 i = hlen + min(icmplen, ICMP_ADVLENMIN);
217 if (m->m_len < i && (m = m_pullup(m, i)) == 0) {
218 icmpstat.icps_tooshort++;
219 return;
220 }
221 ip = mtod(m, struct ip *);
222 m->m_len -= hlen;
223 m->m_data += hlen;
224 icp = mtod(m, struct icmp *);
225 if (in_cksum(m, icmplen)) {
226 icmpstat.icps_checksum++;
227 goto freeit;
228 }
229 m->m_len += hlen;
230 m->m_data -= hlen;
231
232#ifdef ICMPPRINTFS
233 if (icmpprintfs)
234 printf("icmp_input, type %d code %d\n", icp->icmp_type,
235 icp->icmp_code);
236#endif
237
238 /*
239 * Message type specific processing.
240 */
241 if (icp->icmp_type > ICMP_MAXTYPE)
242 goto raw;
243 icmpstat.icps_inhist[icp->icmp_type]++;
244 code = icp->icmp_code;
245 switch (icp->icmp_type) {
246
247 case ICMP_UNREACH:
248 switch (code) {
249 case ICMP_UNREACH_NET:
250 case ICMP_UNREACH_HOST:
251 case ICMP_UNREACH_PROTOCOL:
252 case ICMP_UNREACH_PORT:
253 case ICMP_UNREACH_SRCFAIL:
254 code += PRC_UNREACH_NET;
255 break;
256
257 case ICMP_UNREACH_NEEDFRAG:
258 code = PRC_MSGSIZE;
259 break;
260
261 case ICMP_UNREACH_NET_UNKNOWN:
262 case ICMP_UNREACH_NET_PROHIB:
263 case ICMP_UNREACH_TOSNET:
264 code = PRC_UNREACH_NET;
265 break;
266
267 case ICMP_UNREACH_HOST_UNKNOWN:
268 case ICMP_UNREACH_ISOLATED:
269 case ICMP_UNREACH_HOST_PROHIB:
270 case ICMP_UNREACH_TOSHOST:
271 code = PRC_UNREACH_HOST;
272 break;
273
274 default:
275 goto badcode;
276 }
277 goto deliver;
278
279 case ICMP_TIMXCEED:
280 if (code > 1)
281 goto badcode;
282 code += PRC_TIMXCEED_INTRANS;
283 goto deliver;
284
285 case ICMP_PARAMPROB:
286 if (code > 1)
287 goto badcode;
288 code = PRC_PARAMPROB;
289 goto deliver;
290
291 case ICMP_SOURCEQUENCH:
292 if (code)
293 goto badcode;
294 code = PRC_QUENCH;
295 deliver:
296 /*
297 * Problem with datagram; advise higher level routines.
298 */
299 if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
300 icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) {
301 icmpstat.icps_badlen++;
302 goto freeit;
303 }
304 NTOHS(icp->icmp_ip.ip_len);
305 /* Discard ICMP's in response to multicast packets */
306 if (IN_MULTICAST(ntohl(icp->icmp_ip.ip_dst.s_addr)))
307 goto badcode;
308#ifdef ICMPPRINTFS
309 if (icmpprintfs)
310 printf("deliver to protocol %d\n", icp->icmp_ip.ip_p);
311#endif
312 icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
313#if 1
314 /*
315 * MTU discovery:
316 * If we got a needfrag and there is a host route to the
317 * original destination, and the MTU is not locked, then
318 * set the MTU in the route to the suggested new value
319 * (if given) and then notify as usual. The ULPs will
320 * notice that the MTU has changed and adapt accordingly.
321 * If no new MTU was suggested, then we guess a new one
322 * less than the current value. If the new MTU is
323 * unreasonably small (arbitrarily set at 296), then
324 * we reset the MTU to the interface value and enable the
325 * lock bit, indicating that we are no longer doing MTU
326 * discovery.
327 */
328 if (code == PRC_MSGSIZE) {
329 struct rtentry *rt;
330 int mtu;
331
332 rt = rtalloc1((struct sockaddr *)&icmpsrc, 0,
333 RTF_CLONING | RTF_PRCLONING);
334 if (rt && (rt->rt_flags & RTF_HOST)
335 && !(rt->rt_rmx.rmx_locks & RTV_MTU)) {
336 mtu = ntohs(icp->icmp_nextmtu);
337 if (!mtu)
338 mtu = ip_next_mtu(rt->rt_rmx.rmx_mtu,
339 1);
340#ifdef DEBUG_MTUDISC
341 printf("MTU for %s reduced to %d\n",
342 inet_ntoa(icmpsrc.sin_addr), mtu);
343#endif
344 if (mtu < 296) {
345 /* rt->rt_rmx.rmx_mtu =
346 rt->rt_ifp->if_mtu; */
347 rt->rt_rmx.rmx_locks |= RTV_MTU;
348 } else if (rt->rt_rmx.rmx_mtu > mtu) {
349 rt->rt_rmx.rmx_mtu = mtu;
350 }
351 }
352 if (rt)
353 RTFREE(rt);
354 }
355
356#endif
357 ctlfunc = inetsw[ip_protox[icp->icmp_ip.ip_p]].pr_ctlinput;
358 if (ctlfunc)
359 (*ctlfunc)(code, (struct sockaddr *)&icmpsrc,
360 (caddr_t)&icp->icmp_ip);
361 break;
362
363 badcode:
364 icmpstat.icps_badcode++;
365 break;
366
367 case ICMP_ECHO:
368 icp->icmp_type = ICMP_ECHOREPLY;
369 goto reflect;
370
371 case ICMP_TSTAMP:
372 if (icmplen < ICMP_TSLEN) {
373 icmpstat.icps_badlen++;
374 break;
375 }
376 icp->icmp_type = ICMP_TSTAMPREPLY;
377 icp->icmp_rtime = iptime();
378 icp->icmp_ttime = icp->icmp_rtime; /* bogus, do later! */
379 goto reflect;
380
381 case ICMP_MASKREQ:
382#define satosin(sa) ((struct sockaddr_in *)(sa))
383 if (icmpmaskrepl == 0)
384 break;
385 /*
386 * We are not able to respond with all ones broadcast
387 * unless we receive it over a point-to-point interface.
388 */
389 if (icmplen < ICMP_MASKLEN)
390 break;
391 switch (ip->ip_dst.s_addr) {
392
393 case INADDR_BROADCAST:
394 case INADDR_ANY:
395 icmpdst.sin_addr = ip->ip_src;
396 break;
397
398 default:
399 icmpdst.sin_addr = ip->ip_dst;
400 }
401 ia = (struct in_ifaddr *)ifaof_ifpforaddr(
402 (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
403 if (ia == 0)
404 break;
405 icp->icmp_type = ICMP_MASKREPLY;
406 icp->icmp_mask = ia->ia_sockmask.sin_addr.s_addr;
407 if (ip->ip_src.s_addr == 0) {
408 if (ia->ia_ifp->if_flags & IFF_BROADCAST)
409 ip->ip_src = satosin(&ia->ia_broadaddr)->sin_addr;
410 else if (ia->ia_ifp->if_flags & IFF_POINTOPOINT)
411 ip->ip_src = satosin(&ia->ia_dstaddr)->sin_addr;
412 }
413reflect:
414 ip->ip_len += hlen; /* since ip_input deducts this */
415 icmpstat.icps_reflect++;
416 icmpstat.icps_outhist[icp->icmp_type]++;
417 icmp_reflect(m);
418 return;
419
420 case ICMP_REDIRECT:
421 if (code > 3)
422 goto badcode;
423 if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
424 icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) {
425 icmpstat.icps_badlen++;
426 break;
427 }
428 /*
429 * Short circuit routing redirects to force
430 * immediate change in the kernel's routing
431 * tables. The message is also handed to anyone
432 * listening on a raw socket (e.g. the routing
433 * daemon for use in updating its tables).
434 */
435 icmpgw.sin_addr = ip->ip_src;
436 icmpdst.sin_addr = icp->icmp_gwaddr;
437#ifdef ICMPPRINTFS
438 if (icmpprintfs) {
439 char buf[4 * sizeof "123"];
440 strcpy(buf, inet_ntoa(icp->icmp_ip.ip_dst));
441
442 printf("redirect dst %s to %s\n",
443 buf, inet_ntoa(icp->icmp_gwaddr));
444 }
445#endif
446 icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
447 rtredirect((struct sockaddr *)&icmpsrc,
448 (struct sockaddr *)&icmpdst,
449 (struct sockaddr *)0, RTF_GATEWAY | RTF_HOST,
450 (struct sockaddr *)&icmpgw, (struct rtentry **)0);
451 pfctlinput(PRC_REDIRECT_HOST, (struct sockaddr *)&icmpsrc);
452 break;
453
454 /*
455 * No kernel processing for the following;
456 * just fall through to send to raw listener.
457 */
458 case ICMP_ECHOREPLY:
459 case ICMP_ROUTERADVERT:
460 case ICMP_ROUTERSOLICIT:
461 case ICMP_TSTAMPREPLY:
462 case ICMP_IREQREPLY:
463 case ICMP_MASKREPLY:
464 default:
465 break;
466 }
467
468raw:
469 rip_input(m);
470 return;
471
472freeit:
473 m_freem(m);
474}
475
476/*
477 * Reflect the ip packet back to the source
478 */
479static void
480icmp_reflect(m)
481 struct mbuf *m;
482{
483 register struct ip *ip = mtod(m, struct ip *);
484 register struct in_ifaddr *ia;
485 struct in_addr t;
486 struct mbuf *opts = 0;
487 int optlen = (ip->ip_hl << 2) - sizeof(struct ip);
488
489 if (!in_canforward(ip->ip_src) &&
490 ((ntohl(ip->ip_src.s_addr) & IN_CLASSA_NET) !=
491 (IN_LOOPBACKNET << IN_CLASSA_NSHIFT))) {
492 m_freem(m); /* Bad return address */
493 goto done; /* Ip_output() will check for broadcast */
494 }
495 t = ip->ip_dst;
496 ip->ip_dst = ip->ip_src;
497 /*
498 * If the incoming packet was addressed directly to us,
499 * use dst as the src for the reply. Otherwise (broadcast
500 * or anonymous), use the address which corresponds
501 * to the incoming interface.
502 */
503 for (ia = in_ifaddr; ia; ia = ia->ia_next) {
504 if (t.s_addr == IA_SIN(ia)->sin_addr.s_addr)
505 break;
506 if ((ia->ia_ifp->if_flags & IFF_BROADCAST) &&
507 t.s_addr == satosin(&ia->ia_broadaddr)->sin_addr.s_addr)
508 break;
509 }
510 icmpdst.sin_addr = t;
511 if (ia == (struct in_ifaddr *)0)
512 ia = (struct in_ifaddr *)ifaof_ifpforaddr(
513 (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
514 /*
515 * The following happens if the packet was not addressed to us,
516 * and was received on an interface with no IP address.
517 */
518 if (ia == (struct in_ifaddr *)0)
519 ia = in_ifaddr;
520 t = IA_SIN(ia)->sin_addr;
521 ip->ip_src = t;
522 ip->ip_ttl = MAXTTL;
523
524 if (optlen > 0) {
525 register u_char *cp;
526 int opt, cnt;
527 u_int len;
528
529 /*
530 * Retrieve any source routing from the incoming packet;
531 * add on any record-route or timestamp options.
532 */
533 cp = (u_char *) (ip + 1);
534 if ((opts = ip_srcroute()) == 0 &&
535 (opts = m_gethdr(M_DONTWAIT, MT_HEADER))) {
536 opts->m_len = sizeof(struct in_addr);
537 mtod(opts, struct in_addr *)->s_addr = 0;
538 }
539 if (opts) {
540#ifdef ICMPPRINTFS
541 if (icmpprintfs)
542 printf("icmp_reflect optlen %d rt %d => ",
543 optlen, opts->m_len);
544#endif
545 for (cnt = optlen; cnt > 0; cnt -= len, cp += len) {
546 opt = cp[IPOPT_OPTVAL];
547 if (opt == IPOPT_EOL)
548 break;
549 if (opt == IPOPT_NOP)
550 len = 1;
551 else {
552 len = cp[IPOPT_OLEN];
553 if (len <= 0 || len > cnt)
554 break;
555 }
556 /*
557 * Should check for overflow, but it "can't happen"
558 */
559 if (opt == IPOPT_RR || opt == IPOPT_TS ||
560 opt == IPOPT_SECURITY) {
561 bcopy((caddr_t)cp,
562 mtod(opts, caddr_t) + opts->m_len, len);
563 opts->m_len += len;
564 }
565 }
566 /* Terminate & pad, if necessary */
567 cnt = opts->m_len % 4;
568 if (cnt) {
569 for (; cnt < 4; cnt++) {
570 *(mtod(opts, caddr_t) + opts->m_len) =
571 IPOPT_EOL;
572 opts->m_len++;
573 }
574 }
575#ifdef ICMPPRINTFS
576 if (icmpprintfs)
577 printf("%d\n", opts->m_len);
578#endif
579 }
580 /*
581 * Now strip out original options by copying rest of first
582 * mbuf's data back, and adjust the IP length.
583 */
584 ip->ip_len -= optlen;
585 ip->ip_hl = sizeof(struct ip) >> 2;
586 m->m_len -= optlen;
587 if (m->m_flags & M_PKTHDR)
588 m->m_pkthdr.len -= optlen;
589 optlen += sizeof(struct ip);
590 bcopy((caddr_t)ip + optlen, (caddr_t)(ip + 1),
591 (unsigned)(m->m_len - sizeof(struct ip)));
592 }
593 m->m_flags &= ~(M_BCAST|M_MCAST);
594 icmp_send(m, opts);
595done:
596 if (opts)
597 (void)m_free(opts);
598}
599
600/*
601 * Send an icmp packet back to the ip level,
602 * after supplying a checksum.
603 */
604static void
605icmp_send(m, opts)
606 register struct mbuf *m;
607 struct mbuf *opts;
608{
609 register struct ip *ip = mtod(m, struct ip *);
610 register int hlen;
611 register struct icmp *icp;
612
613 hlen = ip->ip_hl << 2;
614 m->m_data += hlen;
615 m->m_len -= hlen;
616 icp = mtod(m, struct icmp *);
617 icp->icmp_cksum = 0;
618 icp->icmp_cksum = in_cksum(m, ip->ip_len - hlen);
619 m->m_data -= hlen;
620 m->m_len += hlen;
621#ifdef ICMPPRINTFS
622 if (icmpprintfs) {
623 char buf[4 * sizeof "123"];
624 strcpy(buf, inet_ntoa(ip->ip_dst));
625 printf("icmp_send dst %s src %s\n",
626 buf, inet_ntoa(ip->ip_src));
627 }
628#endif
629 (void) ip_output(m, opts, NULL, 0, NULL);
630}
631
632n_time
633iptime()
634{
635 struct timeval atv;
636 u_long t;
637
638 microtime(&atv);
639 t = (atv.tv_sec % (24*60*60)) * 1000 + atv.tv_usec / 1000;
640 return (htonl(t));
641}
642
643#if 1
644/*
645 * Return the next larger or smaller MTU plateau (table from RFC 1191)
646 * given current value MTU. If DIR is less than zero, a larger plateau
647 * is returned; otherwise, a smaller value is returned.
648 */
649static int
650ip_next_mtu(mtu, dir)
651 int mtu;
652 int dir;
653{
654 static int mtutab[] = {
655 65535, 32000, 17914, 8166, 4352, 2002, 1492, 1006, 508, 296,
656 68, 0
657 };
658 int i;
659
660 for (i = 0; i < (sizeof mtutab) / (sizeof mtutab[0]); i++) {
661 if (mtu >= mtutab[i])
662 break;
663 }
664
665 if (dir < 0) {
666 if (i == 0) {
667 return 0;
668 } else {
669 return mtutab[i - 1];
670 }
671 } else {
672 if (mtutab[i] == 0) {
673 return 0;
674 } else if(mtu > mtutab[i]) {
675 return mtutab[i];
676 } else {
677 return mtutab[i + 1];
678 }
679 }
680}
681#endif