Diff: lwip/core/ipv4/ip.c

Revision:

0:8b387bed54c2

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lwip/core/ipv4/ip.c	Mon Jan 10 21:03:11 2011 +0000
@@ -0,0 +1,857 @@
+/**
+ * @file
+ * This is the IPv4 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 <adam@sics.se>
+ *
+ */
+
+#include "lwip/opt.h"
+#include "lwip/ip.h"
+#include "lwip/def.h"
+#include "lwip/mem.h"
+#include "lwip/ip_frag.h"
+#include "lwip/inet_chksum.h"
+#include "lwip/netif.h"
+#include "lwip/icmp.h"
+#include "lwip/igmp.h"
+#include "lwip/raw.h"
+#include "lwip/udp.h"
+#include "lwip/tcp_impl.h"
+#include "lwip/snmp.h"
+#include "lwip/dhcp.h"
+#include "lwip/autoip.h"
+#include "lwip/stats.h"
+#include "arch/perf.h"
+
+#include <string.h>
+
+/** Set this to 0 in the rare case of wanting to call an extra function to
+ * generate the IP checksum (in contrast to calculating it on-the-fly). */
+#ifndef LWIP_INLINE_IP_CHKSUM
+#define LWIP_INLINE_IP_CHKSUM   1
+#endif
+#if LWIP_INLINE_IP_CHKSUM && CHECKSUM_GEN_IP
+#define CHECKSUM_GEN_IP_INLINE  1
+#else
+#define CHECKSUM_GEN_IP_INLINE  0
+#endif
+
+#if LWIP_DHCP || defined(LWIP_IP_ACCEPT_UDP_PORT)
+#define IP_ACCEPT_LINK_LAYER_ADDRESSING 1
+
+/** Some defines for DHCP to let link-layer-addressed packets through while the
+ * netif is down.
+ * To use this in your own application/protocol, define LWIP_IP_ACCEPT_UDP_PORT
+ * to return 1 if the port is accepted and 0 if the port is not accepted.
+ */
+#if LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT)
+/* accept DHCP client port and custom port */
+#define IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(port) (((port) == PP_NTOHS(DHCP_CLIENT_PORT)) \
+         || (LWIP_IP_ACCEPT_UDP_PORT(port)))
+#elif defined(LWIP_IP_ACCEPT_UDP_PORT) /* LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT) */
+/* accept custom port only */
+#define IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(port) (LWIP_IP_ACCEPT_UDP_PORT(dst_port))
+#else /* LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT) */
+/* accept DHCP client port only */
+#define IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(port) ((port) == PP_NTOHS(DHCP_CLIENT_PORT))
+#endif /* LWIP_DHCP && defined(LWIP_IP_ACCEPT_UDP_PORT) */
+
+#else /* LWIP_DHCP */
+#define IP_ACCEPT_LINK_LAYER_ADDRESSING 0
+#endif /* LWIP_DHCP */
+
+/**
+ * The interface that provided the packet for the current callback
+ * invocation.
+ */
+struct netif *current_netif;
+
+/**
+ * Header of the input packet currently being processed.
+ */
+const struct ip_hdr *current_header;
+/** Source IP address of current_header */
+ip_addr_t current_iphdr_src;
+/** Destination IP address of current_header */
+ip_addr_t current_iphdr_dest;
+
+/** The IP header ID of the next outgoing IP packet */
+static u16_t ip_id;
+
+/**
+ * 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.
+ *
+ * @param dest the destination IP address for which to find the route
+ * @return the netif on which to send to reach dest
+ */
+struct netif *
+ip_route(ip_addr_t *dest)
+{
+  struct netif *netif;
+
+  /* iterate through netifs */
+  for(netif = netif_list; netif != NULL; netif = netif->next) {
+    /* network mask matches? */
+    if (netif_is_up(netif)) {
+      if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
+        /* return netif on which to forward IP packet */
+        return netif;
+      }
+    }
+  }
+  if ((netif_default == NULL) || (!netif_is_up(netif_default))) {
+    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_route: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+      ip4_addr1_16(dest), ip4_addr2_16(dest), ip4_addr3_16(dest), ip4_addr4_16(dest)));
+    IP_STATS_INC(ip.rterr);
+    snmp_inc_ipoutnoroutes();
+    return NULL;
+  }
+  /* 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.
+ *
+ * @param p the packet to forward (p->payload points to IP header)
+ * @param iphdr the IP header of the input packet
+ * @param inp the netif on which this packet was received
+ */
+static void
+ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
+{
+  struct netif *netif;
+
+  PERF_START;
+
+  /* RFC3927 2.7: do not forward link-local addresses */
+  if (ip_addr_islinklocal(&current_iphdr_dest)) {
+    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not forwarding LLA %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+      ip4_addr1_16(&current_iphdr_dest), ip4_addr2_16(&current_iphdr_dest),
+      ip4_addr3_16(&current_iphdr_dest), ip4_addr4_16(&current_iphdr_dest)));
+    goto return_noroute;
+  }
+
+  /* Find network interface where to forward this IP packet to. */
+  netif = ip_route(&current_iphdr_dest);
+  if (netif == NULL) {
+    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for %"U16_F".%"U16_F".%"U16_F".%"U16_F" found\n",
+      ip4_addr1_16(&current_iphdr_dest), ip4_addr2_16(&current_iphdr_dest),
+      ip4_addr3_16(&current_iphdr_dest), ip4_addr4_16(&current_iphdr_dest)));
+    goto return_noroute;
+  }
+  /* 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"));
+    goto return_noroute;
+  }
+
+  /* decrement TTL */
+  IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
+  /* send ICMP if TTL == 0 */
+  if (IPH_TTL(iphdr) == 0) {
+    snmp_inc_ipinhdrerrors();
+#if LWIP_ICMP
+    /* Don't send ICMP messages in response to ICMP messages */
+    if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
+      icmp_time_exceeded(p, ICMP_TE_TTL);
+    }
+#endif /* LWIP_ICMP */
+    return;
+  }
+
+  /* Incrementally update the IP checksum. */
+  if (IPH_CHKSUM(iphdr) >= PP_HTONS(0xffff - 0x100)) {
+    IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + PP_HTONS(0x100) + 1);
+  } else {
+    IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + PP_HTONS(0x100));
+  }
+
+  LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+    ip4_addr1_16(&current_iphdr_dest), ip4_addr2_16(&current_iphdr_dest),
+    ip4_addr3_16(&current_iphdr_dest), ip4_addr4_16(&current_iphdr_dest)));
+
+  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, &current_iphdr_dest);
+  return;
+return_noroute:
+  snmp_inc_ipoutnoroutes();
+}
+#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.
+ * 
+ * @param p the received IP packet (p->payload points to IP header)
+ * @param inp the netif on which this packet was received
+ * @return ERR_OK if the packet was processed (could return ERR_* if it wasn't
+ *         processed, but currently always returns ERR_OK)
+ */
+err_t
+ip_input(struct pbuf *p, struct netif *inp)
+{
+  struct ip_hdr *iphdr;
+  struct netif *netif;
+  u16_t iphdr_hlen;
+  u16_t iphdr_len;
+#if IP_ACCEPT_LINK_LAYER_ADDRESSING
+  int check_ip_src=1;
+#endif /* IP_ACCEPT_LINK_LAYER_ADDRESSING */
+
+  IP_STATS_INC(ip.recv);
+  snmp_inc_ipinreceives();
+
+  /* identify the IP header */
+  iphdr = (struct ip_hdr *)p->payload;
+  if (IPH_V(iphdr) != 4) {
+    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_WARNING, ("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 */
+  iphdr_hlen = IPH_HL(iphdr);
+  /* calculate IP header length in bytes */
+  iphdr_hlen *= 4;
+  /* obtain ip length in bytes */
+  iphdr_len = ntohs(IPH_LEN(iphdr));
+
+  /* header length exceeds first pbuf length, or ip length exceeds total pbuf length? */
+  if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len)) {
+    if (iphdr_hlen > p->len) {
+      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
+        ("IP header (len %"U16_F") does not fit in first pbuf (len %"U16_F"), IP packet dropped.\n",
+        iphdr_hlen, p->len));
+    }
+    if (iphdr_len > p->tot_len) {
+      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
+        ("IP (len %"U16_F") is longer than pbuf (len %"U16_F"), IP packet dropped.\n",
+        iphdr_len, p->tot_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, iphdr_hlen) != 0) {
+
+    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
+      ("Checksum (0x%"X16_F") failed, IP packet dropped.\n", inet_chksum(iphdr, iphdr_hlen)));
+    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, iphdr_len);
+
+  /* copy IP addresses to aligned ip_addr_t */
+  ip_addr_copy(current_iphdr_dest, iphdr->dest);
+  ip_addr_copy(current_iphdr_src, iphdr->src);
+
+  /* match packet against an interface, i.e. is this packet for us? */
+#if LWIP_IGMP
+  if (ip_addr_ismulticast(&current_iphdr_dest)) {
+    if ((inp->flags & NETIF_FLAG_IGMP) && (igmp_lookfor_group(inp, &current_iphdr_dest))) {
+      netif = inp;
+    } else {
+      netif = NULL;
+    }
+  } else
+#endif /* LWIP_IGMP */
+  {
+    /* start trying with inp. if that's not acceptable, start walking the
+       list of configured netifs.
+       'first' is used as a boolean to mark whether we started walking the list */
+    int first = 1;
+    netif = inp;
+    do {
+      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",
+          ip4_addr_get_u32(&iphdr->dest), ip4_addr_get_u32(&netif->ip_addr),
+          ip4_addr_get_u32(&iphdr->dest) & ip4_addr_get_u32(&netif->netmask),
+          ip4_addr_get_u32(&netif->ip_addr) & ip4_addr_get_u32(&netif->netmask),
+          ip4_addr_get_u32(&iphdr->dest) & ~ip4_addr_get_u32(&netif->netmask)));
+
+      /* 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(&current_iphdr_dest, &(netif->ip_addr)) ||
+            /* or broadcast on this interface network address? */
+            ip_addr_isbroadcast(&current_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_AUTOIP
+        /* connections to link-local addresses must persist after changing
+           the netif's address (RFC3927 ch. 1.9) */
+        if ((netif->autoip != NULL) &&
+            ip_addr_cmp(&current_iphdr_dest, &(netif->autoip->llipaddr))) {
+          LWIP_DEBUGF(IP_DEBUG, ("ip_input: LLA packet accepted on interface %c%c\n",
+              netif->name[0], netif->name[1]));
+          /* break out of for loop */
+          break;
+        }
+#endif /* LWIP_AUTOIP */
+      }
+      if (first) {
+        first = 0;
+        netif = netif_list;
+      } else {
+        netif = netif->next;
+      }
+      if (netif == inp) {
+        netif = netif->next;
+      }
+    } while(netif != NULL);
+  }
+
+#if IP_ACCEPT_LINK_LAYER_ADDRESSING
+  /* 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 you want to accept private broadcast communication while a netif is down,
+   * define LWIP_IP_ACCEPT_UDP_PORT(dst_port), e.g.:
+   *
+   * #define LWIP_IP_ACCEPT_UDP_PORT(dst_port) ((dst_port) == PP_NTOHS(12345))
+   */
+  if (netif == NULL) {
+    /* remote port is DHCP server? */
+    if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {
+      struct udp_hdr *udphdr = (struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen);
+      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: UDP packet to DHCP client port %"U16_F"\n",
+        ntohs(udphdr->dest)));
+      if (IP_ACCEPT_LINK_LAYER_ADDRESSED_PORT(udphdr->dest)) {
+        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: DHCP packet accepted.\n"));
+        netif = inp;
+        check_ip_src = 0;
+      }
+    }
+  }
+#endif /* IP_ACCEPT_LINK_LAYER_ADDRESSING */
+
+  /* broadcast or multicast packet source address? Compliant with RFC 1122: 3.2.1.3 */
+#if IP_ACCEPT_LINK_LAYER_ADDRESSING
+  /* DHCP servers need 0.0.0.0 to be allowed as source address (RFC 1.1.2.2: 3.2.1.3/a) */
+  if (check_ip_src && !ip_addr_isany(&current_iphdr_src))
+#endif /* IP_ACCEPT_LINK_LAYER_ADDRESSING */
+  {  if ((ip_addr_isbroadcast(&current_iphdr_src, inp)) ||
+         (ip_addr_ismulticast(&current_iphdr_src))) {
+      /* packet source is not valid */
+      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("ip_input: packet source is not valid.\n"));
+      /* free (drop) packet pbufs */
+      pbuf_free(p);
+      IP_STATS_INC(ip.drop);
+      snmp_inc_ipinaddrerrors();
+      snmp_inc_ipindiscards();
+      return ERR_OK;
+    }
+  }
+
+  /* packet not for us? */
+  if (netif == NULL) {
+    /* packet not for us, route or discard */
+    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: packet not for us.\n"));
+#if IP_FORWARD
+    /* non-broadcast packet? */
+    if (!ip_addr_isbroadcast(&current_iphdr_dest, inp)) {
+      /* try to forward IP packet on (other) interfaces */
+      ip_forward(p, iphdr, inp);
+    } else
+#endif /* IP_FORWARD */
+    {
+      snmp_inc_ipinaddrerrors();
+      snmp_inc_ipindiscards();
+    }
+    pbuf_free(p);
+    return ERR_OK;
+  }
+  /* packet consists of multiple fragments? */
+  if ((IPH_OFFSET(iphdr) & PP_HTONS(IP_OFFMASK | IP_MF)) != 0) {
+#if IP_REASSEMBLY /* packet fragment reassembly code present? */
+    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",
+      ntohs(IPH_ID(iphdr)), p->tot_len, ntohs(IPH_LEN(iphdr)), !!(IPH_OFFSET(iphdr) & PP_HTONS(IP_MF)), (ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK)*8));
+    /* reassemble the packet*/
+    p = ip_reass(p);
+    /* packet not fully reassembled yet? */
+    if (p == NULL) {
+      return ERR_OK;
+    }
+    iphdr = (struct ip_hdr *)p->payload;
+#else /* IP_REASSEMBLY == 0, no packet fragment reassembly code present */
+    pbuf_free(p);
+    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since it was fragmented (0x%"X16_F") (while IP_REASSEMBLY == 0).\n",
+      ntohs(IPH_OFFSET(iphdr))));
+    IP_STATS_INC(ip.opterr);
+    IP_STATS_INC(ip.drop);
+    /* unsupported protocol feature */
+    snmp_inc_ipinunknownprotos();
+    return ERR_OK;
+#endif /* IP_REASSEMBLY */
+  }
+
+#if IP_OPTIONS_ALLOWED == 0 /* no support for IP options in the IP header? */
+
+#if LWIP_IGMP
+  /* there is an extra "router alert" option in IGMP messages which we allow for but do not police */
+  if((iphdr_hlen > IP_HLEN) &&  (IPH_PROTO(iphdr) != IP_PROTO_IGMP)) {
+#else
+  if (iphdr_hlen > IP_HLEN) {
+#endif /* LWIP_IGMP */
+    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since there were IP options (while IP_OPTIONS_ALLOWED == 0).\n"));
+    pbuf_free(p);
+    IP_STATS_INC(ip.opterr);
+    IP_STATS_INC(ip.drop);
+    /* unsupported protocol feature */
+    snmp_inc_ipinunknownprotos();
+    return ERR_OK;
+  }
+#endif /* IP_OPTIONS_ALLOWED == 0 */
+
+  /* send to upper layers */
+  LWIP_DEBUGF(IP_DEBUG, ("ip_input: \n"));
+  ip_debug_print(p);
+  LWIP_DEBUGF(IP_DEBUG, ("ip_input: p->len %"U16_F" p->tot_len %"U16_F"\n", p->len, p->tot_len));
+
+  current_netif = inp;
+  current_header = iphdr;
+
+#if LWIP_RAW
+  /* raw input did not eat the packet? */
+  if (raw_input(p, inp) == 0)
+#endif /* LWIP_RAW */
+  {
+
+    switch (IPH_PROTO(iphdr)) {
+#if LWIP_UDP
+    case IP_PROTO_UDP:
+#if LWIP_UDPLITE
+    case IP_PROTO_UDPLITE:
+#endif /* LWIP_UDPLITE */
+      snmp_inc_ipindelivers();
+      udp_input(p, inp);
+      break;
+#endif /* LWIP_UDP */
+#if LWIP_TCP
+    case IP_PROTO_TCP:
+      snmp_inc_ipindelivers();
+      tcp_input(p, inp);
+      break;
+#endif /* LWIP_TCP */
+#if LWIP_ICMP
+    case IP_PROTO_ICMP:
+      snmp_inc_ipindelivers();
+      icmp_input(p, inp);
+      break;
+#endif /* LWIP_ICMP */
+#if LWIP_IGMP
+    case IP_PROTO_IGMP:
+      igmp_input(p, inp, &current_iphdr_dest);
+      break;
+#endif /* LWIP_IGMP */
+    default:
+#if LWIP_ICMP
+      /* send ICMP destination protocol unreachable unless is was a broadcast */
+      if (!ip_addr_isbroadcast(&current_iphdr_dest, inp) &&
+          !ip_addr_ismulticast(&current_iphdr_dest)) {
+        p->payload = iphdr;
+        icmp_dest_unreach(p, ICMP_DUR_PROTO);
+      }
+#endif /* LWIP_ICMP */
+      pbuf_free(p);
+
+      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("Unsupported transport protocol %"U16_F"\n", IPH_PROTO(iphdr)));
+
+      IP_STATS_INC(ip.proterr);
+      IP_STATS_INC(ip.drop);
+      snmp_inc_ipinunknownprotos();
+    }
+  }
+
+  current_netif = NULL;
+  current_header = NULL;
+  ip_addr_set_any(&current_iphdr_src);
+  ip_addr_set_any(&current_iphdr_dest);
+
+  return ERR_OK;
+}
+
+/**
+ * Sends an IP packet on a network interface. This function constructs
+ * the IP header and calculates the IP header checksum. If the source
+ * IP address is NULL, the IP address of the outgoing network
+ * interface is filled in as source address.
+ * If the destination IP address is IP_HDRINCL, p is assumed to already
+ * include an IP header and p->payload points to it instead of the data.
+ *
+ * @param p the packet to send (p->payload points to the data, e.g. next
+            protocol header; if dest == IP_HDRINCL, p already includes an IP
+            header and p->payload points to that IP header)
+ * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
+ *         IP  address of the netif used to send is used as source address)
+ * @param dest the destination IP address to send the packet to
+ * @param ttl the TTL value to be set in the IP header
+ * @param tos the TOS value to be set in the IP header
+ * @param proto the PROTOCOL to be set in the IP header
+ * @param netif the netif on which to send this packet
+ * @return ERR_OK if the packet was sent OK
+ *         ERR_BUF if p doesn't have enough space for IP/LINK headers
+ *         returns errors returned by netif->output
+ *
+ * @note ip_id: RFC791 "some host may be able to simply use
+ *  unique identifiers independent of destination"
+ */
+err_t
+ip_output_if(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
+             u8_t ttl, u8_t tos,
+             u8_t proto, struct netif *netif)
+{
+#if IP_OPTIONS_SEND
+  return ip_output_if_opt(p, src, dest, ttl, tos, proto, netif, NULL, 0);
+}
+
+/**
+ * Same as ip_output_if() but with the possibility to include IP options:
+ *
+ * @ param ip_options pointer to the IP options, copied into the IP header
+ * @ param optlen length of ip_options
+ */
+err_t ip_output_if_opt(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
+       u8_t ttl, u8_t tos, u8_t proto, struct netif *netif, void *ip_options,
+       u16_t optlen)
+{
+#endif /* IP_OPTIONS_SEND */
+  struct ip_hdr *iphdr;
+  ip_addr_t dest_addr;
+#if CHECKSUM_GEN_IP_INLINE
+  u32_t chk_sum = 0;
+#endif /* CHECKSUM_GEN_IP_INLINE */
+
+  /* pbufs passed to IP must have a ref-count of 1 as their payload pointer
+     gets altered as the packet is passed down the stack */
+  LWIP_ASSERT("p->ref == 1", p->ref == 1);
+
+  snmp_inc_ipoutrequests();
+
+  /* Should the IP header be generated or is it already included in p? */
+  if (dest != IP_HDRINCL) {
+    u16_t ip_hlen = IP_HLEN;
+#if IP_OPTIONS_SEND
+    u16_t optlen_aligned = 0;
+    if (optlen != 0) {
+#if CHECKSUM_GEN_IP_INLINE
+      int i;
+#endif /* CHECKSUM_GEN_IP_INLINE */
+      /* round up to a multiple of 4 */
+      optlen_aligned = ((optlen + 3) & ~3);
+      ip_hlen += optlen_aligned;
+      /* First write in the IP options */
+      if (pbuf_header(p, optlen_aligned)) {
+        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output_if_opt: not enough room for IP options in pbuf\n"));
+        IP_STATS_INC(ip.err);
+        snmp_inc_ipoutdiscards();
+        return ERR_BUF;
+      }
+      MEMCPY(p->payload, ip_options, optlen);
+      if (optlen < optlen_aligned) {
+        /* zero the remaining bytes */
+        memset(((char*)p->payload) + optlen, 0, optlen_aligned - optlen);
+      }
+#if CHECKSUM_GEN_IP_INLINE
+      for (i = 0; i < optlen_aligned; i += sizeof(u16_t)) {
+        chk_sum += ((u16_t*)p->payload)[i];
+      }
+#endif /* CHECKSUM_GEN_IP_INLINE */
+    }
+#endif /* IP_OPTIONS_SEND */
+    /* generate IP header */
+    if (pbuf_header(p, IP_HLEN)) {
+      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output: not enough room for IP header in pbuf\n"));
+
+      IP_STATS_INC(ip.err);
+      snmp_inc_ipoutdiscards();
+      return ERR_BUF;
+    }
+
+    iphdr = (struct ip_hdr *)p->payload;
+    LWIP_ASSERT("check that first pbuf can hold struct ip_hdr",
+               (p->len >= sizeof(struct ip_hdr)));
+
+    IPH_TTL_SET(iphdr, ttl);
+    IPH_PROTO_SET(iphdr, proto);
+#if CHECKSUM_GEN_IP_INLINE
+    chk_sum += LWIP_MAKE_U16(proto, ttl);
+#endif /* CHECKSUM_GEN_IP_INLINE */
+
+    /* dest cannot be NULL here */
+    ip_addr_copy(iphdr->dest, *dest);
+#if CHECKSUM_GEN_IP_INLINE
+    chk_sum += ip4_addr_get_u32(&iphdr->dest) & 0xFFFF;
+    chk_sum += ip4_addr_get_u32(&iphdr->dest) >> 16;
+#endif /* CHECKSUM_GEN_IP_INLINE */
+
+    IPH_VHLTOS_SET(iphdr, 4, ip_hlen / 4, tos);
+#if CHECKSUM_GEN_IP_INLINE
+    chk_sum += iphdr->_v_hl_tos;
+#endif /* CHECKSUM_GEN_IP_INLINE */
+    IPH_LEN_SET(iphdr, htons(p->tot_len));
+#if CHECKSUM_GEN_IP_INLINE
+    chk_sum += iphdr->_len;
+#endif /* CHECKSUM_GEN_IP_INLINE */
+    IPH_OFFSET_SET(iphdr, 0);
+    IPH_ID_SET(iphdr, htons(ip_id));
+#if CHECKSUM_GEN_IP_INLINE
+    chk_sum += iphdr->_id;
+#endif /* CHECKSUM_GEN_IP_INLINE */
+    ++ip_id;
+
+    if (ip_addr_isany(src)) {
+      ip_addr_copy(iphdr->src, netif->ip_addr);
+    } else {
+      /* src cannot be NULL here */
+      ip_addr_copy(iphdr->src, *src);
+    }
+
+#if CHECKSUM_GEN_IP_INLINE
+    chk_sum += ip4_addr_get_u32(&iphdr->src) & 0xFFFF;
+    chk_sum += ip4_addr_get_u32(&iphdr->src) >> 16;
+    chk_sum = (chk_sum >> 16) + (chk_sum & 0xFFFF);
+    chk_sum = (chk_sum >> 16) + chk_sum;
+    chk_sum = ~chk_sum;
+    iphdr->_chksum = chk_sum; /* network order */
+#else /* CHECKSUM_GEN_IP_INLINE */
+    IPH_CHKSUM_SET(iphdr, 0);
+#if CHECKSUM_GEN_IP
+    IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, ip_hlen));
+#endif
+#endif /* CHECKSUM_GEN_IP_INLINE */
+  } else {
+    /* IP header already included in p */
+    iphdr = (struct ip_hdr *)p->payload;
+    ip_addr_copy(dest_addr, iphdr->dest);
+    dest = &dest_addr;
+  }
+
+  IP_STATS_INC(ip.xmit);
+
+  LWIP_DEBUGF(IP_DEBUG, ("ip_output_if: %c%c%"U16_F"\n", netif->name[0], netif->name[1], netif->num));
+  ip_debug_print(p);
+
+#if ENABLE_LOOPBACK
+  if (ip_addr_cmp(dest, &netif->ip_addr)) {
+    /* Packet to self, enqueue it for loopback */
+    LWIP_DEBUGF(IP_DEBUG, ("netif_loop_output()"));
+    return netif_loop_output(netif, p, dest);
+  }
+#if LWIP_IGMP
+  if ((p->flags & PBUF_FLAG_MCASTLOOP) != 0) {
+    netif_loop_output(netif, p, dest);
+  }
+#endif /* LWIP_IGMP */
+#endif /* ENABLE_LOOPBACK */
+#if IP_FRAG
+  /* don't fragment if interface has mtu set to 0 [loopif] */
+  if (netif->mtu && (p->tot_len > netif->mtu)) {
+    return ip_frag(p, netif, dest);
+  }
+#endif /* IP_FRAG */
+
+  LWIP_DEBUGF(IP_DEBUG, ("netif->output()"));
+  return netif->output(netif, p, dest);
+}
+
+/**
+ * Simple interface to ip_output_if. It finds the outgoing network
+ * interface and calls upon ip_output_if to do the actual work.
+ *
+ * @param p the packet to send (p->payload points to the data, e.g. next
+            protocol header; if dest == IP_HDRINCL, p already includes an IP
+            header and p->payload points to that IP header)
+ * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
+ *         IP  address of the netif used to send is used as source address)
+ * @param dest the destination IP address to send the packet to
+ * @param ttl the TTL value to be set in the IP header
+ * @param tos the TOS value to be set in the IP header
+ * @param proto the PROTOCOL to be set in the IP header
+ *
+ * @return ERR_RTE if no route is found
+ *         see ip_output_if() for more return values
+ */
+err_t
+ip_output(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
+          u8_t ttl, u8_t tos, u8_t proto)
+{
+  struct netif *netif;
+
+  /* pbufs passed to IP must have a ref-count of 1 as their payload pointer
+     gets altered as the packet is passed down the stack */
+  LWIP_ASSERT("p->ref == 1", p->ref == 1);
+
+  if ((netif = ip_route(dest)) == NULL) {
+    LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+      ip4_addr1_16(dest), ip4_addr2_16(dest), ip4_addr3_16(dest), ip4_addr4_16(dest)));
+    IP_STATS_INC(ip.rterr);
+    return ERR_RTE;
+  }
+
+  return ip_output_if(p, src, dest, ttl, tos, proto, netif);
+}
+
+#if LWIP_NETIF_HWADDRHINT
+/** Like ip_output, but takes and addr_hint pointer that is passed on to netif->addr_hint
+ *  before calling ip_output_if.
+ *
+ * @param p the packet to send (p->payload points to the data, e.g. next
+            protocol header; if dest == IP_HDRINCL, p already includes an IP
+            header and p->payload points to that IP header)
+ * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
+ *         IP  address of the netif used to send is used as source address)
+ * @param dest the destination IP address to send the packet to
+ * @param ttl the TTL value to be set in the IP header
+ * @param tos the TOS value to be set in the IP header
+ * @param proto the PROTOCOL to be set in the IP header
+ * @param addr_hint address hint pointer set to netif->addr_hint before
+ *        calling ip_output_if()
+ *
+ * @return ERR_RTE if no route is found
+ *         see ip_output_if() for more return values
+ */
+err_t
+ip_output_hinted(struct pbuf *p, ip_addr_t *src, ip_addr_t *dest,
+          u8_t ttl, u8_t tos, u8_t proto, u8_t *addr_hint)
+{
+  struct netif *netif;
+  err_t err;
+
+  /* pbufs passed to IP must have a ref-count of 1 as their payload pointer
+     gets altered as the packet is passed down the stack */
+  LWIP_ASSERT("p->ref == 1", p->ref == 1);
+
+  if ((netif = ip_route(dest)) == NULL) {
+    LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
+      ip4_addr1_16(dest), ip4_addr2_16(dest), ip4_addr3_16(dest), ip4_addr4_16(dest)));
+    IP_STATS_INC(ip.rterr);
+    return ERR_RTE;
+  }
+
+  netif->addr_hint = addr_hint;
+  err = ip_output_if(p, src, dest, ttl, tos, proto, netif);
+  netif->addr_hint = NULL;
+
+  return err;
+}
+#endif /* LWIP_NETIF_HWADDRHINT*/
+
+#if IP_DEBUG
+/* Print an IP header by using LWIP_DEBUGF
+ * @param p an IP packet, p->payload pointing to the IP header
+ */
+void
+ip_debug_print(struct pbuf *p)
+{
+  struct ip_hdr *iphdr = (struct ip_hdr *)p->payload;
+  u8_t *payload;
+
+  payload = (u8_t *)iphdr + IP_HLEN;
+
+  LWIP_DEBUGF(IP_DEBUG, ("IP header:\n"));
+  LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
+  LWIP_DEBUGF(IP_DEBUG, ("|%2"S16_F" |%2"S16_F" |  0x%02"X16_F" |     %5"U16_F"     | (v, hl, tos, len)\n",
+                    IPH_V(iphdr),
+                    IPH_HL(iphdr),
+                    IPH_TOS(iphdr),
+                    ntohs(IPH_LEN(iphdr))));
+  LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
+  LWIP_DEBUGF(IP_DEBUG, ("|    %5"U16_F"      |%"U16_F"%"U16_F"%"U16_F"|    %4"U16_F"   | (id, flags, offset)\n",
+                    ntohs(IPH_ID(iphdr)),
+                    ntohs(IPH_OFFSET(iphdr)) >> 15 & 1,
+                    ntohs(IPH_OFFSET(iphdr)) >> 14 & 1,
+                    ntohs(IPH_OFFSET(iphdr)) >> 13 & 1,
+                    ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK));
+  LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
+  LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |    0x%04"X16_F"     | (ttl, proto, chksum)\n",
+                    IPH_TTL(iphdr),
+                    IPH_PROTO(iphdr),
+                    ntohs(IPH_CHKSUM(iphdr))));
+  LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
+  LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  | (src)\n",
+                    ip4_addr1_16(&iphdr->src),
+                    ip4_addr2_16(&iphdr->src),
+                    ip4_addr3_16(&iphdr->src),
+                    ip4_addr4_16(&iphdr->src)));
+  LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
+  LWIP_DEBUGF(IP_DEBUG, ("|  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  |  %3"U16_F"  | (dest)\n",
+                    ip4_addr1_16(&iphdr->dest),
+                    ip4_addr2_16(&iphdr->dest),
+                    ip4_addr3_16(&iphdr->dest),
+                    ip4_addr4_16(&iphdr->dest)));
+  LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
+}
+#endif /* IP_DEBUG */