ip.cpp

00001 /**
00002  * @file
00003  * This is the IPv4 layer implementation for incoming and outgoing IP traffic.
00004  * 
00005  * @see ip_frag.c
00006  *
00007  */
00008 
00009 /*
00010  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
00011  * All rights reserved.
00012  *
00013  * Redistribution and use in source and binary forms, with or without modification,
00014  * are permitted provided that the following conditions are met:
00015  *
00016  * 1. Redistributions of source code must retain the above copyright notice,
00017  *    this list of conditions and the following disclaimer.
00018  * 2. Redistributions in binary form must reproduce the above copyright notice,
00019  *    this list of conditions and the following disclaimer in the documentation
00020  *    and/or other materials provided with the distribution.
00021  * 3. The name of the author may not be used to endorse or promote products
00022  *    derived from this software without specific prior written permission.
00023  *
00024  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
00025  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
00026  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
00027  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
00028  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
00029  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00030  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
00031  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
00032  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
00033  * OF SUCH DAMAGE.
00034  *
00035  * This file is part of the lwIP TCP/IP stack.
00036  *
00037  * Author: Adam Dunkels <adam@sics.se>
00038  *
00039  */
00040 
00041 #include "lwip/opt.h"
00042 #include "lwip/ip.h"
00043 #include "lwip/def.h"
00044 #include "lwip/mem.h"
00045 #include "lwip/ip_frag.h"
00046 #include "lwip/inet_chksum.h"
00047 #include "lwip/netif.h"
00048 #include "lwip/icmp.h"
00049 #include "lwip/igmp.h"
00050 #include "lwip/raw.h"
00051 #include "lwip/udp.h"
00052 #include "lwip/tcp_impl.h"
00053 #include "lwip/snmp.h"
00054 #include "lwip/dhcp.h "
00055 #include "lwip/autoip.h"
00056 #include "lwip/stats.h"
00057 #include "arch/perf.h"
00058 
00059 #include <string.h>
00060 
00061 /**
00062  * The interface that provided the packet for the current callback
00063  * invocation.
00064  */
00065 struct netif *current_netif;
00066 
00067 /**
00068  * Header of the input packet currently being processed.
00069  */
00070 const struct ip_hdr *current_header;
00071 
00072 /**
00073  * Finds the appropriate network interface for a given IP address. It
00074  * searches the list of network interfaces linearly. A match is found
00075  * if the masked IP address of the network interface equals the masked
00076  * IP address given to the function.
00077  *
00078  * @param dest the destination IP address for which to find the route
00079  * @return the netif on which to send to reach dest
00080  */
00081 struct netif *
00082 ip_route(ip_addr_t *dest)
00083 {
00084   struct netif *netif;
00085 
00086   /* iterate through netifs */
00087   for(netif = netif_list; netif != NULL; netif = netif->next) {
00088     /* network mask matches? */
00089     if (netif_is_up(netif)) {
00090       if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
00091         /* return netif on which to forward IP packet */
00092         return netif;
00093       }
00094     }
00095   }
00096   if ((netif_default == NULL) || (!netif_is_up(netif_default))) {
00097     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_route: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
00098       ip4_addr1_16(dest), ip4_addr2_16(dest), ip4_addr3_16(dest), ip4_addr4_16(dest)));
00099     IP_STATS_INC(ip.rterr);
00100     snmp_inc_ipoutnoroutes();
00101     return NULL;
00102   }
00103   /* no matching netif found, use default netif */
00104   return netif_default;
00105 }
00106 
00107 #if IP_FORWARD
00108 /**
00109  * Forwards an IP packet. It finds an appropriate route for the
00110  * packet, decrements the TTL value of the packet, adjusts the
00111  * checksum and outputs the packet on the appropriate interface.
00112  *
00113  * @param p the packet to forward (p->payload points to IP header)
00114  * @param iphdr the IP header of the input packet
00115  * @param inp the netif on which this packet was received
00116  * @return the netif on which the packet was sent (NULL if it wasn't sent)
00117  */
00118 static struct netif *
00119 ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
00120 {
00121   struct netif *netif;
00122   ip_addr_t dest;
00123 
00124   PERF_START;
00125   dest = iphdr->dest;
00126 
00127   /* RFC3927 2.7: do not forward link-local addresses */
00128   if (ip_addr_islinklocal(&dest)) {
00129     LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not forwarding LLA %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
00130       ip4_addr1_16(&dest), ip4_addr2_16(&dest), ip4_addr3_16(&dest), ip4_addr4_16(&dest)));
00131     snmp_inc_ipoutnoroutes();
00132     return (struct netif *)NULL;
00133   }
00134 
00135   /* Find network interface where to forward this IP packet to. */
00136   netif = ip_route(&dest);
00137   if (netif == NULL) {
00138     LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for %"U16_F".%"U16_F".%"U16_F".%"U16_F" found\n",
00139       ip4_addr1_16(&dest), ip4_addr2_16(&dest), ip4_addr3_16(&dest), ip4_addr4_16(&dest)));
00140     snmp_inc_ipoutnoroutes();
00141     return (struct netif *)NULL;
00142   }
00143   /* Do not forward packets onto the same network interface on which
00144    * they arrived. */
00145   if (netif == inp) {
00146     LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
00147     snmp_inc_ipoutnoroutes();
00148     return (struct netif *)NULL;
00149   }
00150 
00151   /* decrement TTL */
00152   IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
00153   /* send ICMP if TTL == 0 */
00154   if (IPH_TTL(iphdr) == 0) {
00155     snmp_inc_ipinhdrerrors();
00156 #if LWIP_ICMP
00157     /* Don't send ICMP messages in response to ICMP messages */
00158     if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
00159       icmp_time_exceeded(p, ICMP_TE_TTL);
00160     }
00161 #endif /* LWIP_ICMP */
00162     return (struct netif *)NULL;
00163   }
00164 
00165   /* Incrementally update the IP checksum. */
00166   if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100)) {
00167     IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100) + 1);
00168   } else {
00169     IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100));
00170   }
00171 
00172   LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
00173     ip4_addr1_16(&dest), ip4_addr2_16(&dest), ip4_addr3_16(&dest), ip4_addr4_16(&dest)));
00174 
00175   IP_STATS_INC(ip.fw);
00176   IP_STATS_INC(ip.xmit);
00177   snmp_inc_ipforwdatagrams();
00178 
00179   PERF_STOP("ip_forward");
00180   /* transmit pbuf on chosen interface */
00181   netif->output(netif, p, &dest);
00182   return netif;
00183 }
00184 #endif /* IP_FORWARD */
00185 
00186 /**
00187  * This function is called by the network interface device driver when
00188  * an IP packet is received. The function does the basic checks of the
00189  * IP header such as packet size being at least larger than the header
00190  * size etc. If the packet was not destined for us, the packet is
00191  * forwarded (using ip_forward). The IP checksum is always checked.
00192  *
00193  * Finally, the packet is sent to the upper layer protocol input function.
00194  * 
00195  * @param p the received IP packet (p->payload points to IP header)
00196  * @param inp the netif on which this packet was received
00197  * @return ERR_OK if the packet was processed (could return ERR_* if it wasn't
00198  *         processed, but currently always returns ERR_OK)
00199  */
00200 err_t
00201 ip_input(struct pbuf *p, struct netif *inp)
00202 {
00203   struct ip_hdr *iphdr;
00204   struct netif *netif;
00205   u16_t iphdr_hlen;
00206   u16_t iphdr_len;
00207 #if LWIP_DHCP
00208   int check_ip_src=1;
00209 #endif /* LWIP_DHCP */
00210 
00211   IP_STATS_INC(ip.recv);
00212   snmp_inc_ipinreceives();
00213 
00214   /* identify the IP header */
00215   iphdr = (struct ip_hdr *)p->payload;
00216   if (IPH_V(iphdr) != 4) {
00217     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_WARNING, ("IP packet dropped due to bad version number %"U16_F"\n", IPH_V(iphdr)));
00218     ip_debug_print(p);
00219     pbuf_free(p);
00220     IP_STATS_INC(ip.err);
00221     IP_STATS_INC(ip.drop);
00222     snmp_inc_ipinhdrerrors();
00223     return ERR_OK;
00224   }
00225 
00226   /* obtain IP header length in number of 32-bit words */
00227   iphdr_hlen = IPH_HL(iphdr);
00228   /* calculate IP header length in bytes */
00229   iphdr_hlen *= 4;
00230   /* obtain ip length in bytes */
00231   iphdr_len = ntohs(IPH_LEN(iphdr));
00232 
00233   /* header length exceeds first pbuf length, or ip length exceeds total pbuf length? */
00234   if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len)) {
00235     if (iphdr_hlen > p->len) {
00236       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00237         ("IP header (len %"U16_F") does not fit in first pbuf (len %"U16_F"), IP packet dropped.\n",
00238         iphdr_hlen, p->len));
00239     }
00240     if (iphdr_len > p->tot_len) {
00241       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00242         ("IP (len %"U16_F") is longer than pbuf (len %"U16_F"), IP packet dropped.\n",
00243         iphdr_len, p->tot_len));
00244     }
00245     /* free (drop) packet pbufs */
00246     pbuf_free(p);
00247     IP_STATS_INC(ip.lenerr);
00248     IP_STATS_INC(ip.drop);
00249     snmp_inc_ipindiscards();
00250     return ERR_OK;
00251   }
00252 
00253   /* verify checksum */
00254 #if CHECKSUM_CHECK_IP
00255   if (inet_chksum(iphdr, iphdr_hlen) != 0) {
00256 
00257     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00258       ("Checksum (0x%"X16_F") failed, IP packet dropped.\n", inet_chksum(iphdr, iphdr_hlen)));
00259     ip_debug_print(p);
00260     pbuf_free(p);
00261     IP_STATS_INC(ip.chkerr);
00262     IP_STATS_INC(ip.drop);
00263     snmp_inc_ipinhdrerrors();
00264     return ERR_OK;
00265   }
00266 #endif
00267 
00268   /* Trim pbuf. This should have been done at the netif layer,
00269    * but we'll do it anyway just to be sure that its done. */
00270   pbuf_realloc(p, iphdr_len);
00271 
00272   /* match packet against an interface, i.e. is this packet for us? */
00273 #if LWIP_IGMP
00274   if (ip_addr_ismulticast(&(iphdr->dest))) {
00275     if ((inp->flags & NETIF_FLAG_IGMP) && (igmp_lookfor_group(inp, &(iphdr->dest)))) {
00276       netif = inp;
00277     } else {
00278       netif = NULL;
00279     }
00280   } else
00281 #endif /* LWIP_IGMP */
00282   {
00283     /* start trying with inp. if that's not acceptable, start walking the
00284        list of configured netifs.
00285        'first' is used as a boolean to mark whether we started walking the list */
00286     int first = 1;
00287     netif = inp;
00288     do {
00289       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",
00290           ip4_addr_get_u32(&iphdr->dest), ip4_addr_get_u32(&netif->ip_addr),
00291           ip4_addr_get_u32(&iphdr->dest) & ip4_addr_get_u32(&netif->netmask),
00292           ip4_addr_get_u32(&netif->ip_addr) & ip4_addr_get_u32(&netif->netmask),
00293           ip4_addr_get_u32(&iphdr->dest) & ~ip4_addr_get_u32(&netif->netmask)));
00294 
00295       /* interface is up and configured? */
00296       if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr)))) {
00297         /* unicast to this interface address? */
00298         if (ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr))
00299             /* or broadcast on this interface network address? */
00300             || ip_addr_isbroadcast(&(iphdr->dest), netif) 
00301             #if 0
00302             /* or is this to our multicast interface? DIRKX */
00303             || ip_addr_ismulticast(&(iphdr->dest))
00304             #endif
00305            ) {
00306           LWIP_DEBUGF(IP_DEBUG, ("ip_input: packet accepted on interface %c%c\n",
00307               netif->name[0], netif->name[1]));
00308           /* break out of for loop */
00309           break;
00310         }
00311 #if LWIP_AUTOIP
00312         /* connections to link-local addresses must persist after changing
00313            the netif's address (RFC3927 ch. 1.9) */
00314         if ((netif->autoip != NULL) &&
00315             ip_addr_cmp(&(iphdr->dest), &(netif->autoip->llipaddr))) {
00316           LWIP_DEBUGF(IP_DEBUG, ("ip_input: LLA packet accepted on interface %c%c\n",
00317               netif->name[0], netif->name[1]));
00318           /* break out of for loop */
00319           break;
00320         }
00321 #endif /* LWIP_AUTOIP */
00322       }
00323       if (first) {
00324         first = 0;
00325         netif = netif_list;
00326       } else {
00327         netif = netif->next;
00328       }
00329       if (netif == inp) {
00330         netif = netif->next;
00331       }
00332     } while(netif != NULL);
00333   }
00334 
00335 #if LWIP_DHCP
00336   /* Pass DHCP messages regardless of destination address. DHCP traffic is addressed
00337    * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.
00338    * According to RFC 1542 section 3.1.1, referred by RFC 2131).
00339    */
00340   if (netif == NULL) {
00341     /* remote port is DHCP server? */
00342     if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {
00343       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: UDP packet to DHCP client port %"U16_F"\n",
00344         ntohs(((struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen))->dest)));
00345       if (ntohs(((struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen))->dest) == DHCP_CLIENT_PORT) {
00346         LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: DHCP packet accepted.\n"));
00347         netif = inp;
00348         check_ip_src = 0;
00349       }
00350     }
00351   }
00352 #endif /* LWIP_DHCP */
00353 
00354   /* broadcast or multicast packet source address? Compliant with RFC 1122: 3.2.1.3 */
00355 #if LWIP_DHCP
00356   /* DHCP servers need 0.0.0.0 to be allowed as source address (RFC 1.1.2.2: 3.2.1.3/a) */
00357   if (check_ip_src && !ip_addr_isany(&iphdr->src))
00358 #endif /* LWIP_DHCP */
00359   {  if ((ip_addr_isbroadcast(&(iphdr->src), inp)) ||
00360          (ip_addr_ismulticast(&(iphdr->src)))) {
00361       /* packet source is not valid */
00362       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("ip_input: packet source is not valid.\n"));
00363       /* free (drop) packet pbufs */
00364       pbuf_free(p);
00365       IP_STATS_INC(ip.drop);
00366       snmp_inc_ipinaddrerrors();
00367       snmp_inc_ipindiscards();
00368       return ERR_OK;
00369     }
00370   }
00371 
00372   /* packet not for us? */
00373   if (netif == NULL) {
00374     /* packet not for us, route or discard */
00375     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: packet not for us.\n"));
00376 #if IP_FORWARD
00377     /* non-broadcast packet? */
00378     if (!ip_addr_isbroadcast(&(iphdr->dest), inp)) {
00379       /* try to forward IP packet on (other) interfaces */
00380       ip_forward(p, iphdr, inp);
00381     } else
00382 #endif /* IP_FORWARD */
00383     {
00384       snmp_inc_ipinaddrerrors();
00385       snmp_inc_ipindiscards();
00386     }
00387     pbuf_free(p);
00388     return ERR_OK;
00389   }
00390   /* packet consists of multiple fragments? */
00391   if ((IPH_OFFSET(iphdr) & htons(IP_OFFMASK | IP_MF)) != 0) {
00392 #if IP_REASSEMBLY /* packet fragment reassembly code present? */
00393     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",
00394       ntohs(IPH_ID(iphdr)), p->tot_len, ntohs(IPH_LEN(iphdr)), !!(IPH_OFFSET(iphdr) & htons(IP_MF)), (ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK)*8));
00395     /* reassemble the packet*/
00396     p = ip_reass(p);
00397     /* packet not fully reassembled yet? */
00398     if (p == NULL) {
00399       return ERR_OK;
00400     }
00401     iphdr = (struct ip_hdr *)p->payload;
00402 #else /* IP_REASSEMBLY == 0, no packet fragment reassembly code present */
00403     pbuf_free(p);
00404     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since it was fragmented (0x%"X16_F") (while IP_REASSEMBLY == 0).\n",
00405       ntohs(IPH_OFFSET(iphdr))));
00406     IP_STATS_INC(ip.opterr);
00407     IP_STATS_INC(ip.drop);
00408     /* unsupported protocol feature */
00409     snmp_inc_ipinunknownprotos();
00410     return ERR_OK;
00411 #endif /* IP_REASSEMBLY */
00412   }
00413 
00414 #if IP_OPTIONS_ALLOWED == 0 /* no support for IP options in the IP header? */
00415 
00416 #if LWIP_IGMP
00417   /* there is an extra "router alert" option in IGMP messages which we allow for but do not police */
00418   if((iphdr_hlen > IP_HLEN) &&  (IPH_PROTO(iphdr) != IP_PROTO_IGMP)) {
00419 #else
00420   if (iphdr_hlen > IP_HLEN) {
00421 #endif /* LWIP_IGMP */
00422     LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since there were IP options (while IP_OPTIONS_ALLOWED == 0).\n"));
00423     pbuf_free(p);
00424     IP_STATS_INC(ip.opterr);
00425     IP_STATS_INC(ip.drop);
00426     /* unsupported protocol feature */
00427     snmp_inc_ipinunknownprotos();
00428     return ERR_OK;
00429   }
00430 #endif /* IP_OPTIONS_ALLOWED == 0 */
00431 
00432   /* send to upper layers */
00433   LWIP_DEBUGF(IP_DEBUG, ("ip_input: \n"));
00434   ip_debug_print(p);
00435   LWIP_DEBUGF(IP_DEBUG, ("ip_input: p->len %"U16_F" p->tot_len %"U16_F"\n", p->len, p->tot_len));
00436 
00437   current_netif = inp;
00438   current_header = iphdr;
00439 
00440 #if LWIP_RAW
00441   /* raw input did not eat the packet? */
00442   if (raw_input(p, inp) == 0)
00443 #endif /* LWIP_RAW */
00444   {
00445 
00446     switch (IPH_PROTO(iphdr)) {
00447 #if LWIP_UDP
00448     case IP_PROTO_UDP:
00449 #if LWIP_UDPLITE
00450     case IP_PROTO_UDPLITE:
00451 #endif /* LWIP_UDPLITE */
00452       snmp_inc_ipindelivers();
00453       udp_input(p, inp);
00454       break;
00455 #endif /* LWIP_UDP */
00456 #if LWIP_TCP
00457     case IP_PROTO_TCP:
00458       snmp_inc_ipindelivers();
00459       tcp_input(p, inp);
00460       break;
00461 #endif /* LWIP_TCP */
00462 #if LWIP_ICMP
00463     case IP_PROTO_ICMP:
00464       snmp_inc_ipindelivers();
00465       icmp_input(p, inp);
00466       break;
00467 #endif /* LWIP_ICMP */
00468 #if LWIP_IGMP
00469     case IP_PROTO_IGMP:
00470       igmp_input(p,inp,&(iphdr->dest));
00471       break;
00472 #endif /* LWIP_IGMP */
00473     default:
00474 #if LWIP_ICMP
00475       /* send ICMP destination protocol unreachable unless is was a broadcast */
00476       if (!ip_addr_isbroadcast(&(iphdr->dest), inp) &&
00477           !ip_addr_ismulticast(&(iphdr->dest))) {
00478         p->payload = iphdr;
00479         icmp_dest_unreach(p, ICMP_DUR_PROTO);
00480       }
00481 #endif /* LWIP_ICMP */
00482       pbuf_free(p);
00483 
00484       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("Unsupported transport protocol %"U16_F"\n", IPH_PROTO(iphdr)));
00485 
00486       IP_STATS_INC(ip.proterr);
00487       IP_STATS_INC(ip.drop);
00488       snmp_inc_ipinunknownprotos();
00489     }
00490   }
00491 
00492   current_netif = NULL;
00493   current_header = NULL;
00494 
00495   return ERR_OK;
00496 }
00497 
00498 /**
00499  * Sends an IP packet on a network interface. This function constructs
00500  * the IP header and calculates the IP header checksum. If the source
00501  * IP address is NULL, the IP address of the outgoing network
00502  * interface is filled in as source address.
00503  * If the destination IP address is IP_HDRINCL, p is assumed to already
00504  * include an IP header and p->payload points to it instead of the data.
00505  *
00506  * @param p the packet to send (p->payload points to the data, e.g. next
00507             protocol header; if dest == IP_HDRINCL, p already includes an IP
00508             header and p->payload points to that IP header)
00509  * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
00510  *         IP  address of the netif used to send is used as source address)
00511  * @param dest the destination IP address to send the packet to
00512  * @param ttl the TTL value to be set in the IP header
00513  * @param tos the TOS value to be set in the IP header
00514  * @param proto the PROTOCOL to be set in the IP header
00515  * @param netif the netif on which to send this packet
00516  * @return ERR_OK if the packet was sent OK
00517  *         ERR_BUF if p doesn't have enough space for IP/LINK headers
00518  *         returns errors returned by netif->output
00519  *
00520  * @note ip_id: RFC791 "some host may be able to simply use
00521  *  unique identifiers independent of destination"
00522  */
00523 err_t
00524 ip_output_if(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
00525              u8_t ttl, u8_t tos,
00526              u8_t proto, struct netif *netif)
00527 {
00528 #if IP_OPTIONS_SEND
00529   return ip_output_if_opt(p, src, dest, ttl, tos, proto, netif, NULL, 0);
00530 }
00531 
00532 /**
00533  * Same as ip_output_if() but with the possibility to include IP options:
00534  *
00535  * @ param ip_options pointer to the IP options, copied into the IP header
00536  * @ param optlen length of ip_options
00537  */
00538 err_t ip_output_if_opt(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
00539        u8_t ttl, u8_t tos, u8_t proto, struct netif *netif, void *ip_options,
00540        u16_t optlen)
00541 {
00542 #endif /* IP_OPTIONS_SEND */
00543   struct ip_hdr *iphdr;
00544   static u16_t ip_id = 0;
00545 
00546   /* pbufs passed to IP must have a ref-count of 1 as their payload pointer
00547      gets altered as the packet is passed down the stack */
00548   LWIP_ASSERT("p->ref == 1", p->ref == 1);
00549 
00550   snmp_inc_ipoutrequests();
00551 
00552   /* Should the IP header be generated or is it already included in p? */
00553   if (dest != IP_HDRINCL) {
00554     u16_t ip_hlen = IP_HLEN;
00555 #if IP_OPTIONS_SEND
00556     u16_t optlen_aligned = 0;
00557     if (optlen != 0) {
00558       /* round up to a multiple of 4 */
00559       optlen_aligned = ((optlen + 3) & ~3);
00560       ip_hlen += optlen_aligned;
00561       /* First write in the IP options */
00562       if (pbuf_header(p, optlen_aligned)) {
00563         LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output_if_opt: not enough room for IP options in pbuf\n"));
00564         IP_STATS_INC(ip.err);
00565         snmp_inc_ipoutdiscards();
00566         return ERR_BUF;
00567       }
00568       MEMCPY(p->payload, ip_options, optlen);
00569       if (optlen < optlen_aligned) {
00570         /* zero the remaining bytes */
00571         memset(((char*)p->payload) + optlen, 0, optlen_aligned - optlen);
00572       }
00573     }
00574 #endif /* IP_OPTIONS_SEND */
00575     /* generate IP header */
00576     if (pbuf_header(p, IP_HLEN)) {
00577       LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output: not enough room for IP header in pbuf\n"));
00578 
00579       IP_STATS_INC(ip.err);
00580       snmp_inc_ipoutdiscards();
00581       return ERR_BUF;
00582     }
00583 
00584     iphdr = (struct ip_hdr *)p->payload;
00585     LWIP_ASSERT("check that first pbuf can hold struct ip_hdr",
00586                (p->len >= sizeof(struct ip_hdr)));
00587 
00588     IPH_TTL_SET(iphdr, ttl);
00589     IPH_PROTO_SET(iphdr, proto);
00590 
00591     /* dest cannot be NULL here */
00592     ip_addr_copy(iphdr->dest, *dest);
00593 
00594     IPH_VHLTOS_SET(iphdr, 4, ip_hlen / 4, tos);
00595     IPH_LEN_SET(iphdr, htons(p->tot_len));
00596     IPH_OFFSET_SET(iphdr, 0);
00597     IPH_ID_SET(iphdr, htons(ip_id));
00598     ++ip_id;
00599 
00600     if (ip_addr_isany(src)) {
00601       ip_addr_copy(iphdr->src, netif->ip_addr);
00602     } else {
00603       /* src cannot be NULL here */
00604       ip_addr_copy(iphdr->src, *src);
00605     }
00606 
00607     IPH_CHKSUM_SET(iphdr, 0);
00608 #if CHECKSUM_GEN_IP
00609     IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, ip_hlen));
00610 #endif
00611   } else {
00612     /* IP header already included in p */
00613     iphdr = (struct ip_hdr *)p->payload;
00614     dest = &(iphdr->dest);
00615   }
00616 
00617   IP_STATS_INC(ip.xmit);
00618 
00619   LWIP_DEBUGF(IP_DEBUG, ("ip_output_if: %c%c%"U16_F"\n", netif->name[0], netif->name[1], netif->num));
00620   ip_debug_print(p);
00621 
00622 #if ENABLE_LOOPBACK
00623   if (ip_addr_cmp(dest, &netif->ip_addr)) {
00624     /* Packet to self, enqueue it for loopback */
00625     LWIP_DEBUGF(IP_DEBUG, ("netif_loop_output()"));
00626     return netif_loop_output(netif, p, dest);
00627   }
00628 #endif /* ENABLE_LOOPBACK */
00629 #if IP_FRAG
00630   /* don't fragment if interface has mtu set to 0 [loopif] */
00631   if (netif->mtu && (p->tot_len > netif->mtu)) {
00632     return ip_frag(p,netif,dest);
00633   }
00634 #endif
00635 
00636   LWIP_DEBUGF(IP_DEBUG, ("netif->output()"));
00637   return netif->output(netif, p, dest);
00638 }
00639 
00640 /**
00641  * Simple interface to ip_output_if. It finds the outgoing network
00642  * interface and calls upon ip_output_if to do the actual work.
00643  *
00644  * @param p the packet to send (p->payload points to the data, e.g. next
00645             protocol header; if dest == IP_HDRINCL, p already includes an IP
00646             header and p->payload points to that IP header)
00647  * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
00648  *         IP  address of the netif used to send is used as source address)
00649  * @param dest the destination IP address to send the packet to
00650  * @param ttl the TTL value to be set in the IP header
00651  * @param tos the TOS value to be set in the IP header
00652  * @param proto the PROTOCOL to be set in the IP header
00653  *
00654  * @return ERR_RTE if no route is found
00655  *         see ip_output_if() for more return values
00656  */
00657 err_t
00658 ip_output(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
00659           u8_t ttl, u8_t tos, u8_t proto)
00660 {
00661   struct netif *netif;
00662 
00663   /* pbufs passed to IP must have a ref-count of 1 as their payload pointer
00664      gets altered as the packet is passed down the stack */
00665   LWIP_ASSERT("p->ref == 1", p->ref == 1);
00666 
00667   if ((netif = ip_route(dest)) == NULL) {
00668     LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
00669       ip4_addr1_16(dest), ip4_addr2_16(dest), ip4_addr3_16(dest), ip4_addr4_16(dest)));
00670     IP_STATS_INC(ip.rterr);
00671     return ERR_RTE;
00672   }
00673 
00674   return ip_output_if(p, src, dest, ttl, tos, proto, netif);
00675 }
00676 
00677 #if LWIP_NETIF_HWADDRHINT
00678 /** Like ip_output, but takes and addr_hint pointer that is passed on to netif->addr_hint
00679  *  before calling ip_output_if.
00680  *
00681  * @param p the packet to send (p->payload points to the data, e.g. next
00682             protocol header; if dest == IP_HDRINCL, p already includes an IP
00683             header and p->payload points to that IP header)
00684  * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
00685  *         IP  address of the netif used to send is used as source address)
00686  * @param dest the destination IP address to send the packet to
00687  * @param ttl the TTL value to be set in the IP header
00688  * @param tos the TOS value to be set in the IP header
00689  * @param proto the PROTOCOL to be set in the IP header
00690  * @param addr_hint address hint pointer set to netif->addr_hint before
00691  *        calling ip_output_if()
00692  *
00693  * @return ERR_RTE if no route is found
00694  *         see ip_output_if() for more return values
00695  */
00696 err_t
00697 ip_output_hinted(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
00698           u8_t ttl, u8_t tos, u8_t proto, u8_t *addr_hint)
00699 {
00700   struct netif *netif;
00701   err_t err;
00702 
00703   /* pbufs passed to IP must have a ref-count of 1 as their payload pointer
00704      gets altered as the packet is passed down the stack */
00705   LWIP_ASSERT("p->ref == 1", p->ref == 1);
00706 
00707   if ((netif = ip_route(dest)) == NULL) {
00708     LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
00709       ip4_addr1_16(dest), ip4_addr2_16(dest), ip4_addr3_16(dest), ip4_addr4_16(dest)));
00710     IP_STATS_INC(ip.rterr);
00711     return ERR_RTE;
00712   }
00713 
00714   netif->addr_hint = addr_hint;
00715   err = ip_output_if(p, src, dest, ttl, tos, proto, netif);
00716   netif->addr_hint = NULL;
00717 
00718   return err;
00719 }
00720 #endif /* LWIP_NETIF_HWADDRHINT*/
00721 
00722 #if IP_DEBUG
00723 /* Print an IP header by using LWIP_DEBUGF
00724  * @param p an IP packet, p->payload pointing to the IP header
00725  */
00726 void
00727 ip_debug_print(struct pbuf *p)
00728 {
00729   struct ip_hdr *iphdr = (struct ip_hdr *) p->payload;
00730   u8_t *payload;
00731 
00732   payload = (u8_t *)iphdr + IP_HLEN;
00733 
00734   LWIP_DEBUGF(IP_DEBUG, ("IP header:\n"));
00735   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
00736   LWIP_DEBUGF(IP_DEBUG, ("|%2"S16_F" |%2"S16_F" |  0x%02"X16_F" |     %5"U16_F"     | (v, hl, tos, len)\n",
00737                     IPH_V(iphdr),
00738                     IPH_HL(iphdr),
00739                     IPH_TOS(iphdr),
00740                     ntohs(IPH_LEN(iphdr))));
00741   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
00742   LWIP_DEBUGF(IP_DEBUG, ("|    %5"U16_F"      |%"U16_F"%"U16_F"%"U16_F"|    %4"U16_F"   | (id, flags, offset)\n",
00743                     ntohs(IPH_ID(iphdr)),
00744                     ntohs(IPH_OFFSET(iphdr)) >> 15 & 1,
00745                     ntohs(IPH_OFFSET(iphdr)) >> 14 & 1,
00746                     ntohs(IPH_OFFSET(iphdr)) >> 13 & 1,
00747                     ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK));
00748   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
00749   LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |    0x%04"X16_F"     | (ttl, proto, chksum)\n",
00750                     IPH_TTL(iphdr),
00751                     IPH_PROTO(iphdr),
00752                     ntohs(IPH_CHKSUM(iphdr))));
00753   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
00754   LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  | (src)\n",
00755                     ip4_addr1_16(&iphdr->src),
00756                     ip4_addr2_16(&iphdr->src),
00757                     ip4_addr3_16(&iphdr->src),
00758                     ip4_addr4_16(&iphdr->src)));
00759   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
00760   LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  | (dest)\n",
00761                     ip4_addr1_16(&iphdr->dest),
00762                     ip4_addr2_16(&iphdr->dest),
00763                     ip4_addr3_16(&iphdr->dest),
00764                     ip4_addr4_16(&iphdr->dest)));
00765   LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
00766 }
00767 #endif /* IP_DEBUG */