ip.c

《嵌入式网络系统设计-基于Atmel ARM7 系列》这个本书的光盘资料

/* @file
 *
 * This is the IP layer implementation for incoming and outgoing IP traffic.
 * 
 * @see ip_frag.c
 *
 */
/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <[e-mail]>
 *
 */

#include "lwip/opt.h"

#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/ip.h"
#include "lwip/ip_frag.h"
#include "lwip/inet.h"
#include "lwip/netif.h"
#include "lwip/icmp.h"
#include "lwip/raw.h"
#include "lwip/udp.h"
#include "lwip/tcp.h"

#include "lwip/stats.h"

#include "arch/perf.h"

#include "lwip/snmp.h"
#if LWIP_DHCP
#  include "lwip/dhcp.h"
#endif /* LWIP_DHCP */


/**
 * Initializes the IP layer.
 */

void
ip_init(void)
{
#if IP_FRAG
  ip_frag_init();
#endif
}

/**
 * Finds the appropriate network interface for a given IP address. It
 * searches the list of network interfaces linearly. A match is found
 * if the masked IP address of the network interface equals the masked
 * IP address given to the function.
 */

struct netif *
ip_route(struct ip_addr *dest)
{
  struct netif *netif;

  /* iterate through netifs */
  for(netif = netif_list; netif != NULL; netif = netif->next) {
    /* network mask matches? */
    if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
      /* return netif on which to forward IP packet */
      return netif;
    }
  }
  /* no matching netif found, use default netif */
  return netif_default;
}
#if IP_FORWARD

/**
 * Forwards an IP packet. It finds an appropriate route for the
 * packet, decrements the TTL value of the packet, adjusts the
 * checksum and outputs the packet on the appropriate interface.
 */

static struct netif *
ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
{
  struct netif *netif;

  PERF_START;
  /* Find network interface where to forward this IP packet to. */
  netif = ip_route((struct ip_addr *)&(iphdr->dest));
  if (netif == NULL) {
    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for 0x%"X32_F" found\n",
                      iphdr->dest.addr));
    snmp_inc_ipoutnoroutes();
    return (struct netif *)NULL;
  }
  /* Do not forward packets onto the same network interface on which
   * they arrived. */
  if (netif == inp) {
    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
    snmp_inc_ipoutnoroutes();
    return (struct netif *)NULL;
  }

  /* decrement TTL */
  IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
  /* send ICMP if TTL == 0 */
  if (IPH_TTL(iphdr) == 0) {
    snmp_inc_ipinhdrerrors();
    /* Don't send ICMP messages in response to ICMP messages */
    if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
      icmp_time_exceeded(p, ICMP_TE_TTL);
    }
    return (struct netif *)NULL;
  }

  /* Incrementally update the IP checksum. */
  if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100)) {
    IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100) + 1);
  } else {
    IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100));
  }

  LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to 0x%"X32_F"\n",
                    iphdr->dest.addr));

  IP_STATS_INC(ip.fw);
  IP_STATS_INC(ip.xmit);
  snmp_inc_ipforwdatagrams();

  PERF_STOP("ip_forward");
  /* transmit pbuf on chosen interface */
  netif->output(netif, p, (struct ip_addr *)&(iphdr->dest));
  return netif;
}
#endif /* IP_FORWARD */

/**
 * This function is called by the network interface device driver when
 * an IP packet is received. The function does the basic checks of the
 * IP header such as packet size being at least larger than the header
 * size etc. If the packet was not destined for us, the packet is
 * forwarded (using ip_forward). The IP checksum is always checked.
 *
 * Finally, the packet is sent to the upper layer protocol input function.
 * 
 * 
 * 
 */

err_t
ip_input(struct pbuf *p, struct netif *inp) {
  struct ip_hdr *iphdr;
  struct netif *netif;
  u16_t iphdrlen;

  IP_STATS_INC(ip.recv);
  snmp_inc_ipinreceives();

  /* identify the IP header */
  iphdr = p->payload;
  if (IPH_V(iphdr) != 4) {
    LWIP_DEBUGF(IP_DEBUG | 1, ("IP packet dropped due to bad version number %"U16_F"\n", IPH_V(iphdr)));
    ip_debug_print(p);
    pbuf_free(p);
    IP_STATS_INC(ip.err);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipinhdrerrors();
    return ERR_OK;
  }
  /* obtain IP header length in number of 32-bit words */
  iphdrlen = IPH_HL(iphdr);
  /* calculate IP header length in bytes */
  iphdrlen *= 4;

  /* header length exceeds first pbuf length? */
  if (iphdrlen > p->len) {
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP header (len %"U16_F") does not fit in first pbuf (len %"U16_F"), IP packet droppped.\n",
      iphdrlen, p->len));
    /* free (drop) packet pbufs */
    pbuf_free(p);
    IP_STATS_INC(ip.lenerr);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipindiscards();
    return ERR_OK;
  }

  /* verify checksum */
#if CHECKSUM_CHECK_IP
  if (inet_chksum(iphdr, iphdrlen) != 0) {

    LWIP_DEBUGF(IP_DEBUG | 2, ("Checksum (0x%"X16_F") failed, IP packet dropped.\n", inet_chksum(iphdr, iphdrlen)));
    ip_debug_print(p);
    pbuf_free(p);
    IP_STATS_INC(ip.chkerr);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipinhdrerrors();
    return ERR_OK;
  }
#endif

  /* Trim pbuf. This should have been done at the netif layer,
   * but we'll do it anyway just to be sure that its done. */
  pbuf_realloc(p, ntohs(IPH_LEN(iphdr)));

  /* match packet against an interface, i.e. is this packet for us? */
  for (netif = netif_list; netif != NULL; netif = netif->next) {

    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",
      iphdr->dest.addr, netif->ip_addr.addr,
      iphdr->dest.addr & netif->netmask.addr,
      netif->ip_addr.addr & netif->netmask.addr,
      iphdr->dest.addr & ~(netif->netmask.addr)));

    /* interface is up and configured? */
    if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr))))
    {
      /* unicast to this interface address? */
      if (ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr)) ||
         /* or broadcast on this interface network address? */
         ip_addr_isbroadcast(&(iphdr->dest), netif)) {
        LWIP_DEBUGF(IP_DEBUG, ("ip_input: packet accepted on interface %c%c\n",
          netif->name[0], netif->name[1]));
        /* break out of for loop */
        break;
      }
    }
  }
#if LWIP_DHCP
  /* Pass DHCP messages regardless of destination address. DHCP traffic is addressed
   * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.
   * According to RFC 1542 section 3.1.1, referred by RFC 2131).
   */
  if (netif == NULL) {
    /* remote port is DHCP server? */
    if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {