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 1.11 1995/11/14 20:34:12 phk 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 <vm/vm.h> 47 #include <sys/sysctl.h> 48 49 #include <net/if.h> 50 #include <net/route.h> 51 52 #include <netinet/in.h> 53 #include <netinet/in_systm.h> 54 #include <netinet/in_var.h> 55 #include <netinet/ip.h> 56 #include <netinet/ip_icmp.h> 57 #include <netinet/ip_var.h> 58 #include <netinet/icmp_var.h> 59 60 /* 61 * ICMP routines: error generation, receive packet processing, and 62 * routines to turnaround packets back to the originator, and 63 * host table maintenance routines. 64 */ 65 66 struct icmpstat icmpstat; 67 SYSCTL_STRUCT(_net_inet_icmp, ICMPCTL_STATS, stats, CTLFLAG_RD, 68 &icmpstat, icmpstat, ""); 69 70 static int icmpmaskrepl = 0; 71 SYSCTL_INT(_net_inet_icmp, ICMPCTL_MASKREPL, maskrepl, CTLFLAG_RW, 72 &icmpmaskrepl, 0, ""); 73 74 #ifdef ICMPPRINTFS 75 int icmpprintfs = 0; 76 #endif 77 78 static void icmp_reflect __P((struct mbuf *)); 79 static void icmp_send __P((struct mbuf *, struct mbuf *)); 80 81 extern struct protosw inetsw[]; 82 83 /* 84 * Generate an error packet of type error 85 * in response to bad packet ip. 86 */ 87 void 88 icmp_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); 175 176 freeit: 177 m_freem(n); 178 } 179 180 static struct sockaddr_in icmpsrc = { sizeof (struct sockaddr_in), AF_INET }; 181 static struct sockaddr_in icmpdst = { sizeof (struct sockaddr_in), AF_INET }; 182 static struct sockaddr_in icmpgw = { sizeof (struct sockaddr_in), AF_INET }; 183 184 /* 185 * Process a received ICMP message. 186 */ 187 void 188 icmp_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 #ifdef MTUDISC 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 if (!mtu || mtu < 296) { 341 rt->rt_rmx.rmx_mtu = 342 rt->rt_ifp->if_mtu; 343 rt->rt_rmx.rmx_locks |= RTV_MTU; 344 } else if (rt->rt_rmx.rmx_mtu > mtu) { 345 rt->rt_rmx.rmx_mtu = mtu; 346 } 347 } 348 if (rt) 349 RTFREE(rt); 350 } 351 352 #endif /* MTUDISC */ 353 ctlfunc = inetsw[ip_protox[icp->icmp_ip.ip_p]].pr_ctlinput; 354 if (ctlfunc) 355 (*ctlfunc)(code, (struct sockaddr *)&icmpsrc, 356 (caddr_t)&icp->icmp_ip); 357 break; 358 359 badcode: 360 icmpstat.icps_badcode++; 361 break; 362 363 case ICMP_ECHO: 364 icp->icmp_type = ICMP_ECHOREPLY; 365 goto reflect; 366 367 case ICMP_TSTAMP: 368 if (icmplen < ICMP_TSLEN) { 369 icmpstat.icps_badlen++; 370 break; 371 } 372 icp->icmp_type = ICMP_TSTAMPREPLY; 373 icp->icmp_rtime = iptime(); 374 icp->icmp_ttime = icp->icmp_rtime; /* bogus, do later! */ 375 goto reflect; 376 377 case ICMP_MASKREQ: 378 #define satosin(sa) ((struct sockaddr_in *)(sa)) 379 if (icmpmaskrepl == 0) 380 break; 381 /* 382 * We are not able to respond with all ones broadcast 383 * unless we receive it over a point-to-point interface. 384 */ 385 if (icmplen < ICMP_MASKLEN) 386 break; 387 switch (ip->ip_dst.s_addr) { 388 389 case INADDR_BROADCAST: 390 case INADDR_ANY: 391 icmpdst.sin_addr = ip->ip_src; 392 break; 393 394 default: 395 icmpdst.sin_addr = ip->ip_dst; 396 } 397 ia = (struct in_ifaddr *)ifaof_ifpforaddr( 398 (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif); 399 if (ia == 0) 400 break; 401 icp->icmp_type = ICMP_MASKREPLY; 402 icp->icmp_mask = ia->ia_sockmask.sin_addr.s_addr; 403 if (ip->ip_src.s_addr == 0) { 404 if (ia->ia_ifp->if_flags & IFF_BROADCAST) 405 ip->ip_src = satosin(&ia->ia_broadaddr)->sin_addr; 406 else if (ia->ia_ifp->if_flags & IFF_POINTOPOINT) 407 ip->ip_src = satosin(&ia->ia_dstaddr)->sin_addr; 408 } 409 reflect: 410 ip->ip_len += hlen; /* since ip_input deducts this */ 411 icmpstat.icps_reflect++; 412 icmpstat.icps_outhist[icp->icmp_type]++; 413 icmp_reflect(m); 414 return; 415 416 case ICMP_REDIRECT: 417 if (code > 3) 418 goto badcode; 419 if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) || 420 icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) { 421 icmpstat.icps_badlen++; 422 break; 423 } 424 /* 425 * Short circuit routing redirects to force 426 * immediate change in the kernel's routing 427 * tables. The message is also handed to anyone 428 * listening on a raw socket (e.g. the routing 429 * daemon for use in updating its tables). 430 */ 431 icmpgw.sin_addr = ip->ip_src; 432 icmpdst.sin_addr = icp->icmp_gwaddr; 433 #ifdef ICMPPRINTFS 434 if (icmpprintfs) { 435 char buf[4 * sizeof "123"]; 436 strcpy(buf, inet_ntoa(icp->icmp_ip.ip_dst)); 437 438 printf("redirect dst %s to %s\n", 439 buf, inet_ntoa(icp->icmp_gwaddr)); 440 } 441 #endif 442 icmpsrc.sin_addr = icp->icmp_ip.ip_dst; 443 rtredirect((struct sockaddr *)&icmpsrc, 444 (struct sockaddr *)&icmpdst, 445 (struct sockaddr *)0, RTF_GATEWAY | RTF_HOST, 446 (struct sockaddr *)&icmpgw, (struct rtentry **)0); 447 pfctlinput(PRC_REDIRECT_HOST, (struct sockaddr *)&icmpsrc); 448 break; 449 450 /* 451 * No kernel processing for the following; 452 * just fall through to send to raw listener. 453 */ 454 case ICMP_ECHOREPLY: 455 case ICMP_ROUTERADVERT: 456 case ICMP_ROUTERSOLICIT: 457 case ICMP_TSTAMPREPLY: 458 case ICMP_IREQREPLY: 459 case ICMP_MASKREPLY: 460 default: 461 break; 462 } 463 464 raw: 465 rip_input(m); 466 return; 467 468 freeit: 469 m_freem(m); 470 } 471 472 /* 473 * Reflect the ip packet back to the source 474 */ 475 static void 476 icmp_reflect(m) 477 struct mbuf *m; 478 { 479 register struct ip *ip = mtod(m, struct ip *); 480 register struct in_ifaddr *ia; 481 struct in_addr t; 482 struct mbuf *opts = 0; 483 int optlen = (ip->ip_hl << 2) - sizeof(struct ip); 484 485 if (!in_canforward(ip->ip_src) && 486 ((ntohl(ip->ip_src.s_addr) & IN_CLASSA_NET) != 487 (IN_LOOPBACKNET << IN_CLASSA_NSHIFT))) { 488 m_freem(m); /* Bad return address */ 489 goto done; /* Ip_output() will check for broadcast */ 490 } 491 t = ip->ip_dst; 492 ip->ip_dst = ip->ip_src; 493 /* 494 * If the incoming packet was addressed directly to us, 495 * use dst as the src for the reply. Otherwise (broadcast 496 * or anonymous), use the address which corresponds 497 * to the incoming interface. 498 */ 499 for (ia = in_ifaddr; ia; ia = ia->ia_next) { 500 if (t.s_addr == IA_SIN(ia)->sin_addr.s_addr) 501 break; 502 if ((ia->ia_ifp->if_flags & IFF_BROADCAST) && 503 t.s_addr == satosin(&ia->ia_broadaddr)->sin_addr.s_addr) 504 break; 505 } 506 icmpdst.sin_addr = t; 507 if (ia == (struct in_ifaddr *)0) 508 ia = (struct in_ifaddr *)ifaof_ifpforaddr( 509 (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif); 510 /* 511 * The following happens if the packet was not addressed to us, 512 * and was received on an interface with no IP address. 513 */ 514 if (ia == (struct in_ifaddr *)0) 515 ia = in_ifaddr; 516 t = IA_SIN(ia)->sin_addr; 517 ip->ip_src = t; 518 ip->ip_ttl = MAXTTL; 519 520 if (optlen > 0) { 521 register u_char *cp; 522 int opt, cnt; 523 u_int len; 524 525 /* 526 * Retrieve any source routing from the incoming packet; 527 * add on any record-route or timestamp options. 528 */ 529 cp = (u_char *) (ip + 1); 530 if ((opts = ip_srcroute()) == 0 && 531 (opts = m_gethdr(M_DONTWAIT, MT_HEADER))) { 532 opts->m_len = sizeof(struct in_addr); 533 mtod(opts, struct in_addr *)->s_addr = 0; 534 } 535 if (opts) { 536 #ifdef ICMPPRINTFS 537 if (icmpprintfs) 538 printf("icmp_reflect optlen %d rt %d => ", 539 optlen, opts->m_len); 540 #endif 541 for (cnt = optlen; cnt > 0; cnt -= len, cp += len) { 542 opt = cp[IPOPT_OPTVAL]; 543 if (opt == IPOPT_EOL) 544 break; 545 if (opt == IPOPT_NOP) 546 len = 1; 547 else { 548 len = cp[IPOPT_OLEN]; 549 if (len <= 0 || len > cnt) 550 break; 551 } 552 /* 553 * Should check for overflow, but it "can't happen" 554 */ 555 if (opt == IPOPT_RR || opt == IPOPT_TS || 556 opt == IPOPT_SECURITY) { 557 bcopy((caddr_t)cp, 558 mtod(opts, caddr_t) + opts->m_len, len); 559 opts->m_len += len; 560 } 561 } 562 /* Terminate & pad, if necessary */ 563 cnt = opts->m_len % 4; 564 if (cnt) { 565 for (; cnt < 4; cnt++) { 566 *(mtod(opts, caddr_t) + opts->m_len) = 567 IPOPT_EOL; 568 opts->m_len++; 569 } 570 } 571 #ifdef ICMPPRINTFS 572 if (icmpprintfs) 573 printf("%d\n", opts->m_len); 574 #endif 575 } 576 /* 577 * Now strip out original options by copying rest of first 578 * mbuf's data back, and adjust the IP length. 579 */ 580 ip->ip_len -= optlen; 581 ip->ip_hl = sizeof(struct ip) >> 2; 582 m->m_len -= optlen; 583 if (m->m_flags & M_PKTHDR) 584 m->m_pkthdr.len -= optlen; 585 optlen += sizeof(struct ip); 586 bcopy((caddr_t)ip + optlen, (caddr_t)(ip + 1), 587 (unsigned)(m->m_len - sizeof(struct ip))); 588 } 589 m->m_flags &= ~(M_BCAST|M_MCAST); 590 icmp_send(m, opts); 591 done: 592 if (opts) 593 (void)m_free(opts); 594 } 595 596 /* 597 * Send an icmp packet back to the ip level, 598 * after supplying a checksum. 599 */ 600 static void 601 icmp_send(m, opts) 602 register struct mbuf *m; 603 struct mbuf *opts; 604 { 605 register struct ip *ip = mtod(m, struct ip *); 606 register int hlen; 607 register struct icmp *icp; 608 609 hlen = ip->ip_hl << 2; 610 m->m_data += hlen; 611 m->m_len -= hlen; 612 icp = mtod(m, struct icmp *); 613 icp->icmp_cksum = 0; 614 icp->icmp_cksum = in_cksum(m, ip->ip_len - hlen); 615 m->m_data -= hlen; 616 m->m_len += hlen; 617 #ifdef ICMPPRINTFS 618 if (icmpprintfs) { 619 char buf[4 * sizeof "123"]; 620 strcpy(buf, inet_ntoa(ip->ip_dst)); 621 printf("icmp_send dst %s src %s\n", 622 buf, inet_ntoa(ip->ip_src)); 623 } 624 #endif 625 (void) ip_output(m, opts, NULL, 0, NULL); 626 } 627 628 n_time 629 iptime() 630 { 631 struct timeval atv; 632 u_long t; 633 634 microtime(&atv); 635 t = (atv.tv_sec % (24*60*60)) * 1000 + atv.tv_usec / 1000; 636 return (htonl(t)); 637 } 638 639 #ifdef MTUDISC 640 /* 641 * Return the next larger or smaller MTU plateau (table from RFC 1191) 642 * given current value MTU. If DIR is less than zero, a larger plateau 643 * is returned; otherwise, a smaller value is returned. 644 */ 645 int 646 ip_next_mtu(mtu, dir) 647 int mtu; 648 int dir; 649 { 650 static int mtutab[] = { 651 65535, 32000, 17914, 8166, 4352, 2002, 1492, 1006, 508, 296, 652 68, 0 653 }; 654 int i; 655 656 for (i = 0; i < (sizeof mtutab) / (sizeof mtutab[0]); i++) { 657 if (mtu >= mtutab[i]) 658 break; 659 } 660 661 if (dir < 0) { 662 if (i == 0) { 663 return 0; 664 } else { 665 return mtutab[i - 1]; 666 } 667 } else { 668 if (mtutab[i] == 0) { 669 return 0; 670 } else if(mtu > mtutab[i]) { 671 return mtutab[i]; 672 } else { 673 return mtutab[i + 1]; 674 } 675 } 676 } 677 #endif /* MTUDISC */ 678