FreeRTOS/Common/ethernet/lwIP_132/src/core/ipv4/ip.c

   1 /**
   2  * @file
   3  * This is the IPv4 layer implementation for incoming and outgoing IP traffic.
   4  *
   5  * @see ip_frag.c
   6  *
   7  */
   8
   9 /*
  10  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
  11  * All rights reserved.
  12  *
  13  * Redistribution and use in source and binary forms, with or without modification,
  14  * are permitted provided that the following conditions are met:
  15  *
  16  * 1. Redistributions of source code must retain the above copyright notice,
  17  *    this list of conditions and the following disclaimer.
  18  * 2. Redistributions in binary form must reproduce the above copyright notice,
  19  *    this list of conditions and the following disclaimer in the documentation
  20  *    and/or other materials provided with the distribution.
  21  * 3. The name of the author may not be used to endorse or promote products
  22  *    derived from this software without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
  25  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  26  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
  27  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  28  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
  29  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  30  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  31  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  32  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
  33  * OF SUCH DAMAGE.
  34  *
  35  * This file is part of the lwIP TCP/IP stack.
  36  *
  37  * Author: Adam Dunkels <adam@sics.se>
  38  *
  39  */
  40
  41 #include "lwip/opt.h"
  42 #include "lwip/ip.h"
  43 #include "lwip/def.h"
  44 #include "lwip/mem.h"
  45 #include "lwip/ip_frag.h"
  46 #include "lwip/inet.h"
  47 #include "lwip/inet_chksum.h"
  48 #include "lwip/netif.h"
  49 #include "lwip/icmp.h"
  50 #include "lwip/igmp.h"
  51 #include "lwip/raw.h"
  52 #include "lwip/udp.h"
  53 #include "lwip/tcp.h"
  54 #include "lwip/snmp.h"
  55 #include "lwip/dhcp.h"
  56 #include "lwip/stats.h"
  57 #include "arch/perf.h"
  58
  59 #include <string.h>
  60
  61 /**
  62  * The interface that provided the packet for the current callback
  63  * invocation.
  64  */
  65 struct netif *current_netif;
  66
  67 /**
  68  * Header of the input packet currently being processed.
  69  */
  70 const struct ip_hdr *current_header;
  71
  72 /**
  73  * Finds the appropriate network interface for a given IP address. It
  74  * searches the list of network interfaces linearly. A match is found
  75  * if the masked IP address of the network interface equals the masked
  76  * IP address given to the function.
  77  *
  78  * @param dest the destination IP address for which to find the route
  79  * @return the netif on which to send to reach dest
  80  */
  81 struct netif *
  82 ip_route(struct ip_addr *dest)
  83 {
  84   struct netif *netif;
  85
  86   /* iterate through netifs */
  87   for(netif = netif_list; netif != NULL; netif = netif->next) {
  88     /* network mask matches? */
  89     if (netif_is_up(netif)) {
  90       if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
  91         /* return netif on which to forward IP packet */
  92         return netif;
  93       }
  94     }
  95   }
  96   if ((netif_default == NULL) || (!netif_is_up(netif_default))) {
  97     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_route: No route to 0x%"X32_F"\n", dest->addr));
  98     IP_STATS_INC(ip.rterr);
  99     snmp_inc_ipoutnoroutes();
 100     return NULL;
 101   }
 102   /* no matching netif found, use default netif */
 103   return netif_default;
 104 }
 105
 106 #if IP_FORWARD
 107 /**
 108  * Forwards an IP packet. It finds an appropriate route for the
 109  * packet, decrements the TTL value of the packet, adjusts the
 110  * checksum and outputs the packet on the appropriate interface.
 111  *
 112  * @param p the packet to forward (p->payload points to IP header)
 113  * @param iphdr the IP header of the input packet
 114  * @param inp the netif on which this packet was received
 115  * @return the netif on which the packet was sent (NULL if it wasn't sent)
 116  */
 117 static struct netif *
 118 ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
 119 {
 120   struct netif *netif;
 121
 122   PERF_START;
 123   /* Find network interface where to forward this IP packet to. */
 124   netif = ip_route((struct ip_addr *)&(iphdr->dest));
 125   if (netif == NULL) {
 126     LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for 0x%"X32_F" found\n",
 127                       iphdr->dest.addr));
 128     snmp_inc_ipoutnoroutes();
 129     return (struct netif *)NULL;
 130   }
 131   /* Do not forward packets onto the same network interface on which
 132    * they arrived. */
 133   if (netif == inp) {
 134     LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
 135     snmp_inc_ipoutnoroutes();
 136     return (struct netif *)NULL;
 137   }
 138
 139   /* decrement TTL */
 140   IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
 141   /* send ICMP if TTL == 0 */
 142   if (IPH_TTL(iphdr) == 0) {
 143     snmp_inc_ipinhdrerrors();
 144 #if LWIP_ICMP
 145     /* Don't send ICMP messages in response to ICMP messages */
 146     if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
 147       icmp_time_exceeded(p, ICMP_TE_TTL);
 148     }
 149 #endif /* LWIP_ICMP */
 150     return (struct netif *)NULL;
 151   }
 152
 153   /* Incrementally update the IP checksum. */
 154   if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100)) {
 155     IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100) + 1);
 156   } else {
 157     IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100));
 158   }
 159
 160   LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to 0x%"X32_F"\n",
 161                     iphdr->dest.addr));
 162
 163   IP_STATS_INC(ip.fw);
 164   IP_STATS_INC(ip.xmit);
 165   snmp_inc_ipforwdatagrams();
 166
 167   PERF_STOP("ip_forward");
 168   /* transmit pbuf on chosen interface */
 169   netif->output(netif, p, (struct ip_addr *)&(iphdr->dest));
 170   return netif;
 171 }
 172 #endif /* IP_FORWARD */
 173
 174 /**
 175  * This function is called by the network interface device driver when
 176  * an IP packet is received. The function does the basic checks of the
 177  * IP header such as packet size being at least larger than the header
 178  * size etc. If the packet was not destined for us, the packet is
 179  * forwarded (using ip_forward). The IP checksum is always checked.
 180  *
 181  * Finally, the packet is sent to the upper layer protocol input function.
 182  *
 183  * @param p the received IP packet (p->payload points to IP header)
 184  * @param inp the netif on which this packet was received
 185  * @return ERR_OK if the packet was processed (could return ERR_* if it wasn't
 186  *         processed, but currently always returns ERR_OK)
 187  */
 188 err_t
 189 ip_input(struct pbuf *p, struct netif *inp)
 190 {
 191   struct ip_hdr *iphdr;
 192   struct netif *netif;
 193   u16_t iphdr_hlen;
 194   u16_t iphdr_len;
 195 #if LWIP_DHCP
 196   int check_ip_src=1;
 197 #endif /* LWIP_DHCP */
 198
 199   IP_STATS_INC(ip.recv);
 200   snmp_inc_ipinreceives();
 201
 202   /* identify the IP header */
 203   iphdr = p->payload;
 204   if (IPH_V(iphdr) != 4) {
 205     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_WARNING, ("IP packet dropped due to bad version number %"U16_F"\n", IPH_V(iphdr)));
 206     ip_debug_print(p);
 207     pbuf_free(p);
 208     IP_STATS_INC(ip.err);
 209     IP_STATS_INC(ip.drop);
 210     snmp_inc_ipinhdrerrors();
 211     return ERR_OK;
 212   }
 213
 214   /* obtain IP header length in number of 32-bit words */
 215   iphdr_hlen = IPH_HL(iphdr);
 216   /* calculate IP header length in bytes */
 217   iphdr_hlen *= 4;
 218   /* obtain ip length in bytes */
 219   iphdr_len = ntohs(IPH_LEN(iphdr));
 220
 221   /* header length exceeds first pbuf length, or ip length exceeds total pbuf length? */
 222   if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len)) {
 223     if (iphdr_hlen > p->len) {
 224       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
 225         ("IP header (len %"U16_F") does not fit in first pbuf (len %"U16_F"), IP packet dropped.\n",
 226         iphdr_hlen, p->len));
 227     }
 228     if (iphdr_len > p->tot_len) {
 229       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
 230         ("IP (len %"U16_F") is longer than pbuf (len %"U16_F"), IP packet dropped.\n",
 231         iphdr_len, p->tot_len));
 232     }
 233     /* free (drop) packet pbufs */
 234     pbuf_free(p);
 235     IP_STATS_INC(ip.lenerr);
 236     IP_STATS_INC(ip.drop);
 237     snmp_inc_ipindiscards();
 238     return ERR_OK;
 239   }
 240
 241   /* verify checksum */
 242 #if CHECKSUM_CHECK_IP
 243   if (inet_chksum(iphdr, iphdr_hlen) != 0) {
 244
 245     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
 246       ("Checksum (0x%"X16_F") failed, IP packet dropped.\n", inet_chksum(iphdr, iphdr_hlen)));
 247     ip_debug_print(p);
 248     pbuf_free(p);
 249     IP_STATS_INC(ip.chkerr);
 250     IP_STATS_INC(ip.drop);
 251     snmp_inc_ipinhdrerrors();
 252     return ERR_OK;
 253   }
 254 #endif
 255
 256   /* Trim pbuf. This should have been done at the netif layer,
 257    * but we'll do it anyway just to be sure that its done. */
 258   pbuf_realloc(p, iphdr_len);
 259
 260   /* match packet against an interface, i.e. is this packet for us? */
 261 #if LWIP_IGMP
 262   if (ip_addr_ismulticast(&(iphdr->dest))) {
 263     if ((inp->flags & NETIF_FLAG_IGMP) && (igmp_lookfor_group(inp, &(iphdr->dest)))) {
 264       netif = inp;
 265     } else {
 266       netif = NULL;
 267     }
 268   } else
 269 #endif /* LWIP_IGMP */
 270   {
 271     /* start trying with inp. if that's not acceptable, start walking the
 272        list of configured netifs.
 273        'first' is used as a boolean to mark whether we started walking the list */
 274     int first = 1;
 275     netif = inp;
 276     do {
 277       LWIP_DEBUGF(IP_DEBUG, ("ip_input: iphdr->dest 0x%"X32_F" netif->ip_addr 0x%"X32_F" (0x%"X32_F", 0x%"X32_F", 0x%"X32_F")\n",
 278           iphdr->dest.addr, netif->ip_addr.addr,
 279           iphdr->dest.addr & netif->netmask.addr,
 280           netif->ip_addr.addr & netif->netmask.addr,
 281           iphdr->dest.addr & ~(netif->netmask.addr)));
 282
 283       /* interface is up and configured? */
 284       if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr)))) {
 285         /* unicast to this interface address? */
 286         if (ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr)) ||
 287             /* or broadcast on this interface network address? */
 288             ip_addr_isbroadcast(&(iphdr->dest), netif)) {
 289           LWIP_DEBUGF(IP_DEBUG, ("ip_input: packet accepted on interface %c%c\n",
 290               netif->name[0], netif->name[1]));
 291           /* break out of for loop */
 292           break;
 293         }
 294       }
 295       if (first) {
 296         first = 0;
 297         netif = netif_list;
 298       } else {
 299         netif = netif->next;
 300       }
 301       if (netif == inp) {
 302         netif = netif->next;
 303       }
 304     } while(netif != NULL);
 305   }
 306
 307 #if LWIP_DHCP
 308   /* Pass DHCP messages regardless of destination address. DHCP traffic is addressed
 309    * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.
 310    * According to RFC 1542 section 3.1.1, referred by RFC 2131).
 311    */
 312   if (netif == NULL) {
 313     /* remote port is DHCP server? */
 314     if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {
 315       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: UDP packet to DHCP client port %"U16_F"\n",
 316         ntohs(((struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen))->dest)));
 317       if (ntohs(((struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen))->dest) == DHCP_CLIENT_PORT) {
 318         LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: DHCP packet accepted.\n"));
 319         netif = inp;
 320         check_ip_src = 0;
 321       }
 322     }
 323   }
 324 #endif /* LWIP_DHCP */
 325
 326   /* broadcast or multicast packet source address? Compliant with RFC 1122: 3.2.1.3 */
 327 #if LWIP_DHCP
 328   /* DHCP servers need 0.0.0.0 to be allowed as source address (RFC 1.1.2.2: 3.2.1.3/a) */
 329   if (check_ip_src && (iphdr->src.addr != 0))
 330 #endif /* LWIP_DHCP */
 331   {  if ((ip_addr_isbroadcast(&(iphdr->src), inp)) ||
 332          (ip_addr_ismulticast(&(iphdr->src)))) {
 333       /* packet source is not valid */
 334       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("ip_input: packet source is not valid.\n"));
 335       /* free (drop) packet pbufs */
 336       pbuf_free(p);
 337       IP_STATS_INC(ip.drop);
 338       snmp_inc_ipinaddrerrors();
 339       snmp_inc_ipindiscards();
 340       return ERR_OK;
 341     }
 342   }
 343
 344   /* packet not for us? */
 345   if (netif == NULL) {
 346     /* packet not for us, route or discard */
 347     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: packet not for us.\n"));
 348 #if IP_FORWARD
 349     /* non-broadcast packet? */
 350     if (!ip_addr_isbroadcast(&(iphdr->dest), inp)) {
 351       /* try to forward IP packet on (other) interfaces */
 352       ip_forward(p, iphdr, inp);
 353     } else
 354 #endif /* IP_FORWARD */
 355     {
 356       snmp_inc_ipinaddrerrors();
 357       snmp_inc_ipindiscards();
 358     }
 359     pbuf_free(p);
 360     return ERR_OK;
 361   }
 362   /* packet consists of multiple fragments? */
 363   if ((IPH_OFFSET(iphdr) & htons(IP_OFFMASK | IP_MF)) != 0) {
 364 #if IP_REASSEMBLY /* packet fragment reassembly code present? */
 365     LWIP_DEBUGF(IP_DEBUG, ("IP packet is a fragment (id=0x%04"X16_F" tot_len=%"U16_F" len=%"U16_F" MF=%"U16_F" offset=%"U16_F"), calling ip_reass()\n",
 366       ntohs(IPH_ID(iphdr)), p->tot_len, ntohs(IPH_LEN(iphdr)), !!(IPH_OFFSET(iphdr) & htons(IP_MF)), (ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK)*8));
 367     /* reassemble the packet*/
 368     p = ip_reass(p);
 369     /* packet not fully reassembled yet? */
 370     if (p == NULL) {
 371       return ERR_OK;
 372     }
 373     iphdr = p->payload;
 374 #else /* IP_REASSEMBLY == 0, no packet fragment reassembly code present */
 375     pbuf_free(p);
 376     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since it was fragmented (0x%"X16_F") (while IP_REASSEMBLY == 0).\n",
 377       ntohs(IPH_OFFSET(iphdr))));
 378     IP_STATS_INC(ip.opterr);
 379     IP_STATS_INC(ip.drop);
 380     /* unsupported protocol feature */
 381     snmp_inc_ipinunknownprotos();
 382     return ERR_OK;
 383 #endif /* IP_REASSEMBLY */
 384   }
 385
 386 #if IP_OPTIONS_ALLOWED == 0 /* no support for IP options in the IP header? */
 387
 388 #if LWIP_IGMP
 389   /* there is an extra "router alert" option in IGMP messages which we allow for but do not police */
 390   if((iphdr_hlen > IP_HLEN &&  (IPH_PROTO(iphdr) != IP_PROTO_IGMP)) {
 391 #else
 392   if (iphdr_hlen > IP_HLEN) {
 393 #endif /* LWIP_IGMP */
 394     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since there were IP options (while IP_OPTIONS_ALLOWED == 0).\n"));
 395     pbuf_free(p);
 396     IP_STATS_INC(ip.opterr);
 397     IP_STATS_INC(ip.drop);
 398     /* unsupported protocol feature */
 399     snmp_inc_ipinunknownprotos();
 400     return ERR_OK;
 401   }
 402 #endif /* IP_OPTIONS_ALLOWED == 0 */
 403
 404   /* send to upper layers */
 405   LWIP_DEBUGF(IP_DEBUG, ("ip_input: \n"));
 406   ip_debug_print(p);
 407   LWIP_DEBUGF(IP_DEBUG, ("ip_input: p->len %"U16_F" p->tot_len %"U16_F"\n", p->len, p->tot_len));
 408
 409   current_netif = inp;
 410   current_header = iphdr;
 411
 412 #if LWIP_RAW
 413   /* raw input did not eat the packet? */
 414   if (raw_input(p, inp) == 0)
 415 #endif /* LWIP_RAW */
 416   {
 417
 418     switch (IPH_PROTO(iphdr)) {
 419 #if LWIP_UDP
 420     case IP_PROTO_UDP:
 421 #if LWIP_UDPLITE
 422     case IP_PROTO_UDPLITE:
 423 #endif /* LWIP_UDPLITE */
 424       snmp_inc_ipindelivers();
 425       udp_input(p, inp);
 426       break;
 427 #endif /* LWIP_UDP */
 428 #if LWIP_TCP
 429     case IP_PROTO_TCP:
 430       snmp_inc_ipindelivers();
 431       tcp_input(p, inp);
 432       break;
 433 #endif /* LWIP_TCP */
 434 #if LWIP_ICMP
 435     case IP_PROTO_ICMP:
 436       snmp_inc_ipindelivers();
 437       icmp_input(p, inp);
 438       break;
 439 #endif /* LWIP_ICMP */
 440 #if LWIP_IGMP
 441     case IP_PROTO_IGMP:
 442       igmp_input(p,inp,&(iphdr->dest));
 443       break;
 444 #endif /* LWIP_IGMP */
 445     default:
 446 #if LWIP_ICMP
 447       /* send ICMP destination protocol unreachable unless is was a broadcast */
 448       if (!ip_addr_isbroadcast(&(iphdr->dest), inp) &&
 449           !ip_addr_ismulticast(&(iphdr->dest))) {
 450         p->payload = iphdr;
 451         icmp_dest_unreach(p, ICMP_DUR_PROTO);
 452       }
 453 #endif /* LWIP_ICMP */
 454       pbuf_free(p);
 455
 456       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("Unsupported transport protocol %"U16_F"\n", IPH_PROTO(iphdr)));
 457
 458       IP_STATS_INC(ip.proterr);
 459       IP_STATS_INC(ip.drop);
 460       snmp_inc_ipinunknownprotos();
 461     }
 462   }
 463
 464   current_netif = NULL;
 465   current_header = NULL;
 466
 467   return ERR_OK;
 468 }
 469
 470 /**
 471  * Sends an IP packet on a network interface. This function constructs
 472  * the IP header and calculates the IP header checksum. If the source
 473  * IP address is NULL, the IP address of the outgoing network
 474  * interface is filled in as source address.
 475  * If the destination IP address is IP_HDRINCL, p is assumed to already
 476  * include an IP header and p->payload points to it instead of the data.
 477  *
 478  * @param p the packet to send (p->payload points to the data, e.g. next
 479             protocol header; if dest == IP_HDRINCL, p already includes an IP
 480             header and p->payload points to that IP header)
 481  * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 482  *         IP  address of the netif used to send is used as source address)
 483  * @param dest the destination IP address to send the packet to
 484  * @param ttl the TTL value to be set in the IP header
 485  * @param tos the TOS value to be set in the IP header
 486  * @param proto the PROTOCOL to be set in the IP header
 487  * @param netif the netif on which to send this packet
 488  * @return ERR_OK if the packet was sent OK
 489  *         ERR_BUF if p doesn't have enough space for IP/LINK headers
 490  *         returns errors returned by netif->output
 491  *
 492  * @note ip_id: RFC791 "some host may be able to simply use
 493  *  unique identifiers independent of destination"
 494  */
 495 err_t
 496 ip_output_if(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
 497              u8_t ttl, u8_t tos,
 498              u8_t proto, struct netif *netif)
 499 {
 500 #if IP_OPTIONS_SEND
 501   return ip_output_if_opt(p, src, dest, ttl, tos, proto, netif, NULL, 0);
 502 }
 503
 504 /**
 505  * Same as ip_output_if() but with the possibility to include IP options:
 506  *
 507  * @ param ip_options pointer to the IP options, copied into the IP header
 508  * @ param optlen length of ip_options
 509  */
 510 err_t ip_output_if_opt(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
 511        u8_t ttl, u8_t tos, u8_t proto, struct netif *netif, void *ip_options,
 512        u16_t optlen)
 513 {
 514 #endif /* IP_OPTIONS_SEND */
 515   struct ip_hdr *iphdr;
 516   static u16_t ip_id = 0;
 517
 518   snmp_inc_ipoutrequests();
 519
 520   /* Should the IP header be generated or is it already included in p? */
 521   if (dest != IP_HDRINCL) {
 522     u16_t ip_hlen = IP_HLEN;
 523 #if IP_OPTIONS_SEND
 524     u16_t optlen_aligned = 0;
 525     if (optlen != 0) {
 526       /* round up to a multiple of 4 */
 527       optlen_aligned = ((optlen + 3) & ~3);
 528       ip_hlen += optlen_aligned;
 529       /* First write in the IP options */
 530       if (pbuf_header(p, optlen_aligned)) {
 531         LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output_if_opt: not enough room for IP options in pbuf\n"));
 532         IP_STATS_INC(ip.err);
 533         snmp_inc_ipoutdiscards();
 534         return ERR_BUF;
 535       }
 536       MEMCPY(p->payload, ip_options, optlen);
 537       if (optlen < optlen_aligned) {
 538         /* zero the remaining bytes */
 539         memset(((char*)p->payload) + optlen, 0, optlen_aligned - optlen);
 540       }
 541     }
 542 #endif /* IP_OPTIONS_SEND */
 543     /* generate IP header */
 544     if (pbuf_header(p, IP_HLEN)) {
 545       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output: not enough room for IP header in pbuf\n"));
 546
 547       IP_STATS_INC(ip.err);
 548       snmp_inc_ipoutdiscards();
 549       return ERR_BUF;
 550     }
 551
 552     iphdr = p->payload;
 553     LWIP_ASSERT("check that first pbuf can hold struct ip_hdr",
 554                (p->len >= sizeof(struct ip_hdr)));
 555
 556     IPH_TTL_SET(iphdr, ttl);
 557     IPH_PROTO_SET(iphdr, proto);
 558
 559     ip_addr_set(&(iphdr->dest), dest);
 560
 561     IPH_VHLTOS_SET(iphdr, 4, ip_hlen / 4, tos);
 562     IPH_LEN_SET(iphdr, htons(p->tot_len));
 563     IPH_OFFSET_SET(iphdr, 0);
 564     IPH_ID_SET(iphdr, htons(ip_id));
 565     ++ip_id;
 566
 567     if (ip_addr_isany(src)) {
 568       ip_addr_set(&(iphdr->src), &(netif->ip_addr));
 569     } else {
 570       ip_addr_set(&(iphdr->src), src);
 571     }
 572
 573     IPH_CHKSUM_SET(iphdr, 0);
 574 #if CHECKSUM_GEN_IP
 575     IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, ip_hlen));
 576 #endif
 577   } else {
 578     /* IP header already included in p */
 579     iphdr = p->payload;
 580     dest = &(iphdr->dest);
 581   }
 582
 583   IP_STATS_INC(ip.xmit);
 584
 585   LWIP_DEBUGF(IP_DEBUG, ("ip_output_if: %c%c%"U16_F"\n", netif->name[0], netif->name[1], netif->num));
 586   ip_debug_print(p);
 587
 588 #if ENABLE_LOOPBACK
 589   if (ip_addr_cmp(dest, &netif->ip_addr)) {
 590     /* Packet to self, enqueue it for loopback */
 591     LWIP_DEBUGF(IP_DEBUG, ("netif_loop_output()"));
 592     return netif_loop_output(netif, p, dest);
 593   }
 594 #endif /* ENABLE_LOOPBACK */
 595 #if IP_FRAG
 596   /* don't fragment if interface has mtu set to 0 [loopif] */
 597   if (netif->mtu && (p->tot_len > netif->mtu)) {
 598     return ip_frag(p,netif,dest);
 599   }
 600 #endif
 601
 602   LWIP_DEBUGF(IP_DEBUG, ("netif->output()"));
 603   return netif->output(netif, p, dest);
 604 }
 605
 606 /**
 607  * Simple interface to ip_output_if. It finds the outgoing network
 608  * interface and calls upon ip_output_if to do the actual work.
 609  *
 610  * @param p the packet to send (p->payload points to the data, e.g. next
 611             protocol header; if dest == IP_HDRINCL, p already includes an IP
 612             header and p->payload points to that IP header)
 613  * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 614  *         IP  address of the netif used to send is used as source address)
 615  * @param dest the destination IP address to send the packet to
 616  * @param ttl the TTL value to be set in the IP header
 617  * @param tos the TOS value to be set in the IP header
 618  * @param proto the PROTOCOL to be set in the IP header
 619  *
 620  * @return ERR_RTE if no route is found
 621  *         see ip_output_if() for more return values
 622  */
 623 err_t
 624 ip_output(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
 625           u8_t ttl, u8_t tos, u8_t proto)
 626 {
 627   struct netif *netif;
 628
 629   if ((netif = ip_route(dest)) == NULL) {
 630     LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to 0x%"X32_F"\n", dest->addr));
 631     IP_STATS_INC(ip.rterr);
 632     return ERR_RTE;
 633   }
 634
 635   return ip_output_if(p, src, dest, ttl, tos, proto, netif);
 636 }
 637
 638 #if LWIP_NETIF_HWADDRHINT
 639 /** Like ip_output, but takes and addr_hint pointer that is passed on to netif->addr_hint
 640  *  before calling ip_output_if.
 641  *
 642  * @param p the packet to send (p->payload points to the data, e.g. next
 643             protocol header; if dest == IP_HDRINCL, p already includes an IP
 644             header and p->payload points to that IP header)
 645  * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 646  *         IP  address of the netif used to send is used as source address)
 647  * @param dest the destination IP address to send the packet to
 648  * @param ttl the TTL value to be set in the IP header
 649  * @param tos the TOS value to be set in the IP header
 650  * @param proto the PROTOCOL to be set in the IP header
 651  * @param addr_hint address hint pointer set to netif->addr_hint before
 652  *        calling ip_output_if()
 653  *
 654  * @return ERR_RTE if no route is found
 655  *         see ip_output_if() for more return values
 656  */
 657 err_t
 658 ip_output_hinted(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
 659           u8_t ttl, u8_t tos, u8_t proto, u8_t *addr_hint)
 660 {
 661   struct netif *netif;
 662   err_t err;
 663
 664   if ((netif = ip_route(dest)) == NULL) {
 665     LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to 0x%"X32_F"\n", dest->addr));
 666     IP_STATS_INC(ip.rterr);
 667     return ERR_RTE;
 668   }
 669
 670   netif->addr_hint = addr_hint;
 671   err = ip_output_if(p, src, dest, ttl, tos, proto, netif);
 672   netif->addr_hint = NULL;
 673
 674   return err;
 675 }
 676 #endif /* LWIP_NETIF_HWADDRHINT*/
 677
 678 #if IP_DEBUG
 679 /* Print an IP header by using LWIP_DEBUGF
 680  * @param p an IP packet, p->payload pointing to the IP header
 681  */
 682 void
 683 ip_debug_print(struct pbuf *p)
 684 {
 685   struct ip_hdr *iphdr = p->payload;
 686   u8_t *payload;
 687
 688   payload = (u8_t *)iphdr + IP_HLEN;
 689
 690   LWIP_DEBUGF(IP_DEBUG, ("IP header:\n"));
 691   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
 692   LWIP_DEBUGF(IP_DEBUG, ("|%2"S16_F" |%2"S16_F" |  0x%02"X16_F" |     %5"U16_F"     | (v, hl, tos, len)\n",
 693                     IPH_V(iphdr),
 694                     IPH_HL(iphdr),
 695                     IPH_TOS(iphdr),
 696                     ntohs(IPH_LEN(iphdr))));
 697   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
 698   LWIP_DEBUGF(IP_DEBUG, ("|    %5"U16_F"      |%"U16_F"%"U16_F"%"U16_F"|    %4"U16_F"   | (id, flags, offset)\n",
 699                     ntohs(IPH_ID(iphdr)),
 700                     ntohs(IPH_OFFSET(iphdr)) >> 15 & 1,
 701                     ntohs(IPH_OFFSET(iphdr)) >> 14 & 1,
 702                     ntohs(IPH_OFFSET(iphdr)) >> 13 & 1,
 703                     ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK));
 704   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
 705   LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |    0x%04"X16_F"     | (ttl, proto, chksum)\n",
 706                     IPH_TTL(iphdr),
 707                     IPH_PROTO(iphdr),
 708                     ntohs(IPH_CHKSUM(iphdr))));
 709   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
 710   LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  | (src)\n",
 711                     ip4_addr1(&iphdr->src),
 712                     ip4_addr2(&iphdr->src),
 713                     ip4_addr3(&iphdr->src),
 714                     ip4_addr4(&iphdr->src)));
 715   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
 716   LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  | (dest)\n",
 717                     ip4_addr1(&iphdr->dest),
 718                     ip4_addr2(&iphdr->dest),
 719                     ip4_addr3(&iphdr->dest),
 720                     ip4_addr4(&iphdr->dest)));
 721   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
 722 }
 723 #endif /* IP_DEBUG */