handling replies continuously from server
[oweals/gnunet.git] / src / exit / gnunet-daemon-exit.c
index a2b6d9c8aeced8e740b779670da72df4838dae6d..e58611cc62b37fd68fc1981b2b9afa3f90281722 100644 (file)
@@ -219,6 +219,11 @@ struct TunnelState
 };
 
 
+/**
+ * Return value from 'main'.
+ */
+static int global_ret;
+
 /**
  * The handle to the configuration used throughout the process
  */
@@ -232,13 +237,29 @@ static struct GNUNET_HELPER_Handle *helper_handle;
 /**
  * Arguments to the exit helper.
  */
-static char *exit_argv[7];
+static char *exit_argv[8];
+
+/**
+ * IPv6 address of our TUN interface.
+ */
+static struct in6_addr exit_ipv6addr;
 
 /**
  * IPv6 prefix (0..127) from configuration file.
  */
 static unsigned long long ipv6prefix;
 
+/**
+ * IPv4 address of our TUN interface.
+ */
+static struct in_addr exit_ipv4addr;
+
+/**
+ * IPv4 netmask of our TUN interface.
+ */
+static struct in_addr exit_ipv4mask;
+
+
 /**
  * Statistics.
  */
@@ -263,7 +284,7 @@ static struct GNUNET_CONTAINER_Heap *connections_heap;
 /**
  * If there are at least this many connections, old ones will be removed
  */
-static long long unsigned int max_connections;
+static unsigned long long max_connections;
 
 /**
  * This hashmaps saves interesting things about the configured UDP services
@@ -374,6 +395,13 @@ get_redirect_state (int af,
   GNUNET_HashCode key;
   struct TunnelState *state;
 
+  if ( ( (af == AF_INET) && (protocol == IPPROTO_ICMP) ) ||
+       ( (af == AF_INET6) && (protocol == IPPROTO_ICMPV6) ) )
+  {
+    /* ignore ports */
+    destination_port = 0;
+    local_port = 0;
+  }
   ri.remote_address.af = af;
   if (af == AF_INET)
     ri.remote_address.address.ipv4 = *((struct in_addr*) destination_ip);
@@ -409,17 +437,17 @@ get_redirect_state (int af,
  *
  * @param service_map map of services (TCP or UDP)
  * @param desc service descriptor
- * @param dpt destination port
+ * @param destination_port destination port
  * @return NULL if we are not aware of such a service
  */
 static struct LocalService *
 find_service (struct GNUNET_CONTAINER_MultiHashMap *service_map,
              const GNUNET_HashCode *desc,
-             uint16_t dpt)
+             uint16_t destination_port)
 {
   char key[sizeof (GNUNET_HashCode) + sizeof (uint16_t)];
 
-  memcpy (&key[0], &dpt, sizeof (uint16_t));
+  memcpy (&key[0], &destination_port, sizeof (uint16_t));
   memcpy (&key[sizeof(uint16_t)], desc, sizeof (GNUNET_HashCode));
   return GNUNET_CONTAINER_multihashmap_get (service_map,
                                            (GNUNET_HashCode *) key);
@@ -453,13 +481,13 @@ free_service_record (void *cls,
  *
  * @param service_map map of services (TCP or UDP)
  * @param name name of the service 
- * @param dpt destination port
+ * @param destination_port destination port
  * @param service service information record to store (service->name will be set).
  */
 static void
 store_service (struct GNUNET_CONTAINER_MultiHashMap *service_map,
               const char *name,
-              uint16_t dpt,
+              uint16_t destination_port,
               struct LocalService *service)
 {
   char key[sizeof (GNUNET_HashCode) + sizeof (uint16_t)];
@@ -467,7 +495,7 @@ store_service (struct GNUNET_CONTAINER_MultiHashMap *service_map,
 
   GNUNET_CRYPTO_hash (name, strlen (name) + 1, &desc);
   service->name = GNUNET_strdup (name);
-  memcpy (&key[0], &dpt, sizeof (uint16_t));
+  memcpy (&key[0], &destination_port, sizeof (uint16_t));
   memcpy (&key[sizeof(uint16_t)], &desc, sizeof (GNUNET_HashCode));
   if (GNUNET_OK !=
       GNUNET_CONTAINER_multihashmap_put (service_map,
@@ -479,7 +507,7 @@ store_service (struct GNUNET_CONTAINER_MultiHashMap *service_map,
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                _("Got duplicate service records for `%s:%u'\n"),
                name,
-               (unsigned int) dpt);
+               (unsigned int) destination_port);
   }
 }
 
@@ -501,6 +529,20 @@ send_to_peer_notify_callback (void *cls, size_t size, void *buf)
 
   s->th = NULL;
   tnq = s->head;
+  if (NULL == tnq)
+    return 0;
+  if (0 == size)
+  {
+    s->th = GNUNET_MESH_notify_transmit_ready (tunnel, 
+                                              GNUNET_NO /* corking */, 
+                                              0 /* priority */,
+                                              GNUNET_TIME_UNIT_FOREVER_REL,
+                                              NULL,
+                                              tnq->len,
+                                              &send_to_peer_notify_callback,
+                                              s);
+    return 0;
+  }
   GNUNET_assert (size >= tnq->len);
   memcpy (buf, tnq->payload, tnq->len);
   size = tnq->len;
@@ -528,55 +570,212 @@ send_to_peer_notify_callback (void *cls, size_t size, void *buf)
  * Send the given packet via the mesh tunnel.
  *
  * @param mesh_tunnel destination
- * @param payload message to transmit
- * @param payload_length number of bytes in payload
- * @param desc descriptor to add before payload (optional)
- * @param mtype message type to use
+ * @param tnq message to queue
  */
 static void
 send_packet_to_mesh_tunnel (struct GNUNET_MESH_Tunnel *mesh_tunnel,
-                           const void *payload,
-                           size_t payload_length,
-                           const GNUNET_HashCode *desc,
-                           uint16_t mtype)
+                           struct TunnelMessageQueue *tnq)
 {
   struct TunnelState *s;
+
+  s = GNUNET_MESH_tunnel_get_data (mesh_tunnel);
+  GNUNET_assert (NULL != s);
+  GNUNET_CONTAINER_DLL_insert_tail (s->head, s->tail, tnq);
+  if (NULL == s->th)
+    s->th = GNUNET_MESH_notify_transmit_ready (mesh_tunnel, GNUNET_NO /* cork */, 0 /* priority */,
+                                              GNUNET_TIME_UNIT_FOREVER_REL,
+                                              NULL, tnq->len,
+                                              &send_to_peer_notify_callback,
+                                              s);
+}
+
+
+/**
+ * @brief Handles an ICMP packet received from the helper.
+ *
+ * @param icmp A pointer to the Packet
+ * @param pktlen number of bytes in 'icmp'
+ * @param af address family (AFINET or AF_INET6)
+ * @param destination_ip destination IP-address of the IP packet (should 
+ *                       be our local address)
+ * @param source_ip original source IP-address of the IP packet (should
+ *                       be the original destination address)
+ */
+static void
+icmp_from_helper (const struct GNUNET_TUN_IcmpHeader *icmp, 
+                 size_t pktlen,
+                 int af,
+                 const void *destination_ip, 
+                 const void *source_ip)
+{
+  struct TunnelState *state;
   struct TunnelMessageQueue *tnq;
-  struct GNUNET_MessageHeader *msg;
-  size_t len;
-  GNUNET_HashCode *dp;
+  struct GNUNET_EXIT_IcmpToVPNMessage *i2v;
+  const struct GNUNET_TUN_IPv4Header *ipv4;
+  const struct GNUNET_TUN_IPv6Header *ipv6;
+  const struct GNUNET_TUN_UdpHeader *udp;
+  size_t mlen;
+  uint16_t source_port;
+  uint16_t destination_port;
+  uint8_t protocol;
 
-  len = sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode) + payload_length;
-  if (len >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
   {
+    char sbuf[INET6_ADDRSTRLEN];
+    char dbuf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Received ICMP packet going from %s to %s\n",
+               inet_ntop (af,
+                          source_ip,
+                          sbuf, sizeof (sbuf)),
+               inet_ntop (af,
+                          destination_ip,
+                          dbuf, sizeof (dbuf)));    
+  }
+  if (pktlen < sizeof (struct GNUNET_TUN_IcmpHeader))
+  {
+    /* blame kernel */
     GNUNET_break (0);
     return;
   }
-  tnq = GNUNET_malloc (sizeof (struct TunnelMessageQueue) + len);
-  tnq->payload = &tnq[1];
-  tnq->len = len;
-  msg = (struct GNUNET_MessageHeader *) &tnq[1];
-  msg->size = htons ((uint16_t) len);
-  msg->type = htons (mtype);
-  if (NULL != desc)
+
+  /* Find out if this is an ICMP packet in response to an existing
+     TCP/UDP packet and if so, figure out ports / protocol of the
+     existing session from the IP data in the ICMP payload */
+  source_port = 0;
+  destination_port = 0;
+  switch (af)
+  {
+  case AF_INET:
+    protocol = IPPROTO_ICMP;
+    switch (icmp->type)
+      {
+      case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
+      case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
+       break;
+      case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
+      case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
+      case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:
+       if (pktlen < 
+           sizeof (struct GNUNET_TUN_IcmpHeader) +
+           sizeof (struct GNUNET_TUN_IPv4Header) + 8)
+       {
+         /* blame kernel */
+         GNUNET_break (0);
+         return;
+       }
+       ipv4 = (const struct GNUNET_TUN_IPv4Header *) &icmp[1];
+       protocol = ipv4->protocol;
+       /* could be TCP or UDP, but both have the ports in the right
+          place, so that doesn't matter here */
+       udp = (const struct GNUNET_TUN_UdpHeader *) &ipv4[1];
+       /* swap ports, as they are from the original message */
+       destination_port = ntohs (udp->source_port);
+       source_port = ntohs (udp->destination_port);
+       /* throw away ICMP payload, won't be useful for the other side anyway */
+       pktlen = sizeof (struct GNUNET_TUN_IcmpHeader);
+       break;
+      default:
+       GNUNET_STATISTICS_update (stats,
+                                 gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
+                                 1, GNUNET_NO);
+       return;
+      }
+    break;
+  case AF_INET6:
+    protocol = IPPROTO_ICMPV6;
+    switch (icmp->type)
+      {
+      case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
+      case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
+      case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
+      case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
+       if (pktlen < 
+           sizeof (struct GNUNET_TUN_IcmpHeader) +
+           sizeof (struct GNUNET_TUN_IPv6Header) + 8)
+       {
+         /* blame kernel */
+         GNUNET_break (0);
+         return;
+       }
+       ipv6 = (const struct GNUNET_TUN_IPv6Header *) &icmp[1];
+       protocol = ipv6->next_header;
+       /* could be TCP or UDP, but both have the ports in the right
+          place, so that doesn't matter here */
+       udp = (const struct GNUNET_TUN_UdpHeader *) &ipv6[1];
+       /* swap ports, as they are from the original message */
+       destination_port = ntohs (udp->source_port);
+       source_port = ntohs (udp->destination_port);
+       /* throw away ICMP payload, won't be useful for the other side anyway */
+       pktlen = sizeof (struct GNUNET_TUN_IcmpHeader);
+       break;
+      case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
+      case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
+       break;
+      default:
+       GNUNET_STATISTICS_update (stats,
+                                 gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
+                                 1, GNUNET_NO);
+       return;
+      }
+    break;
+  default:
+    GNUNET_assert (0);
+  }
+  switch (protocol)
   {
-    dp = (GNUNET_HashCode *) &msg[1];
-    *dp = *desc;  
-    memcpy (&dp[1], payload, payload_length);
+  case IPPROTO_ICMP:
+    state = get_redirect_state (af, IPPROTO_ICMP,
+                               source_ip, 0,
+                               destination_ip, 0,
+                               NULL);
+    break;
+  case IPPROTO_ICMPV6:
+    state = get_redirect_state (af, IPPROTO_ICMPV6,
+                               source_ip, 0,
+                               destination_ip, 0,
+                               NULL);
+    break;
+  case IPPROTO_UDP:
+    state = get_redirect_state (af, IPPROTO_UDP,
+                               source_ip,
+                               source_port,
+                               destination_ip,
+                               destination_port,
+                               NULL);
+    break;
+  case IPPROTO_TCP:
+    state = get_redirect_state (af, IPPROTO_TCP,
+                               source_ip,
+                               source_port,
+                               destination_ip,
+                               destination_port,
+                               NULL);
+    break;
+  default:
+    GNUNET_STATISTICS_update (stats,
+                             gettext_noop ("# ICMP packets dropped (not allowed)"),
+                             1, GNUNET_NO);
+    return;
   }
-  else
+  if (NULL == state)
   {
-    memcpy (&msg[1], payload, payload_length);
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+               _("ICMP Packet dropped, have no matching connection information\n"));
+    return;
   }
-  s = GNUNET_MESH_tunnel_get_data (mesh_tunnel);
-  GNUNET_assert (NULL != s);
-  GNUNET_CONTAINER_DLL_insert_tail (s->head, s->tail, tnq);
-  if (NULL == s->th)
-    s->th = GNUNET_MESH_notify_transmit_ready (mesh_tunnel, GNUNET_NO /* cork */, 0 /* priority */,
-                                              GNUNET_TIME_UNIT_FOREVER_REL,
-                                              NULL, len,
-                                              &send_to_peer_notify_callback,
-                                              s);
+  mlen = sizeof (struct GNUNET_EXIT_IcmpToVPNMessage) + pktlen - sizeof (struct GNUNET_TUN_IcmpHeader);
+  tnq = GNUNET_malloc (sizeof (struct TunnelMessageQueue) + mlen);  
+  tnq->payload = &tnq[1];
+  tnq->len = mlen;
+  i2v = (struct GNUNET_EXIT_IcmpToVPNMessage *) &tnq[1];
+  i2v->header.size = htons ((uint16_t) mlen);
+  i2v->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_VPN);
+  i2v->af = htonl (af);
+  memcpy (&i2v->icmp_header,
+         icmp,
+         pktlen);
+  send_packet_to_mesh_tunnel (state->tunnel,
+                             tnq);
 }
 
 
@@ -599,6 +798,9 @@ udp_from_helper (const struct GNUNET_TUN_UdpHeader *udp,
                 const void *source_ip)
 {
   struct TunnelState *state;
+  struct TunnelMessageQueue *tnq;
+  struct GNUNET_EXIT_UdpReplyMessage *urm;
+  size_t mlen;
 
   {
     char sbuf[INET6_ADDRSTRLEN];
@@ -608,11 +810,11 @@ udp_from_helper (const struct GNUNET_TUN_UdpHeader *udp,
                inet_ntop (af,
                           source_ip,
                           sbuf, sizeof (sbuf)),
-               (unsigned int) ntohs (udp->spt),
+               (unsigned int) ntohs (udp->source_port),
                inet_ntop (af,
-                          source_ip,
+                          destination_ip,
                           dbuf, sizeof (dbuf)),
-               (unsigned int) ntohs (udp->dpt));
+               (unsigned int) ntohs (udp->destination_port));
   }
   if (pktlen < sizeof (struct GNUNET_TUN_UdpHeader))
   {
@@ -628,20 +830,30 @@ udp_from_helper (const struct GNUNET_TUN_UdpHeader *udp,
   }
   state = get_redirect_state (af, IPPROTO_UDP,
                              source_ip,
-                             ntohs (udp->spt),
+                             ntohs (udp->source_port),
                              destination_ip,
-                             ntohs (udp->dpt),
+                             ntohs (udp->destination_port),
                              NULL);
   if (NULL == state)
   {
     GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-               _("Packet dropped, have no matching connection information\n"));
+               _("UDP Packet dropped, have no matching connection information\n"));
     return;
   }
+  mlen = sizeof (struct GNUNET_EXIT_UdpReplyMessage) + pktlen - sizeof (struct GNUNET_TUN_UdpHeader);
+  tnq = GNUNET_malloc (sizeof (struct TunnelMessageQueue) + mlen);  
+  tnq->payload = &tnq[1];
+  tnq->len = mlen;
+  urm = (struct GNUNET_EXIT_UdpReplyMessage *) &tnq[1];
+  urm->header.size = htons ((uint16_t) mlen);
+  urm->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_UDP_REPLY);
+  urm->source_port = htons (0);
+  urm->destination_port = htons (0);
+  memcpy (&urm[1],
+         &udp[1],
+         pktlen - sizeof (struct GNUNET_TUN_UdpHeader));
   send_packet_to_mesh_tunnel (state->tunnel,
-                             &udp[1], pktlen - sizeof (struct GNUNET_TUN_UdpHeader),
-                             NULL,
-                             GNUNET_MESSAGE_TYPE_VPN_UDP_REPLY);
+                             tnq);
 }
 
 
@@ -649,7 +861,7 @@ udp_from_helper (const struct GNUNET_TUN_UdpHeader *udp,
  * @brief Handles a TCP packet received from the helper.
  *
  * @param tcp A pointer to the Packet
- * @param pktlen the length of the packet, including its header
+ * @param pktlen the length of the packet, including its TCP header
  * @param af address family (AFINET or AF_INET6)
  * @param destination_ip destination IP-address of the IP packet (should 
  *                       be our local address)
@@ -664,22 +876,26 @@ tcp_from_helper (const struct GNUNET_TUN_TcpHeader *tcp,
                 const void *source_ip)
 {
   struct TunnelState *state;
-  char buf[pktlen];
+  char buf[pktlen] GNUNET_ALIGN;
   struct GNUNET_TUN_TcpHeader *mtcp;
+  struct GNUNET_EXIT_TcpDataMessage *tdm;
+  struct TunnelMessageQueue *tnq;
+  size_t mlen;
 
   {
     char sbuf[INET6_ADDRSTRLEN];
     char dbuf[INET6_ADDRSTRLEN];
     GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-               "Received TCP packet going from %s:%u to %s:%u\n",
+               "Received TCP packet with %u bytes going from %s:%u to %s:%u\n",
+               pktlen - sizeof (struct GNUNET_TUN_TcpHeader),
                inet_ntop (af,
                           source_ip,
                           sbuf, sizeof (sbuf)),
-               (unsigned int) ntohs (tcp->spt),
+               (unsigned int) ntohs (tcp->source_port),
                inet_ntop (af,
-                          source_ip,
+                          destination_ip,
                           dbuf, sizeof (dbuf)),
-               (unsigned int) ntohs (tcp->dpt));
+               (unsigned int) ntohs (tcp->destination_port));
   }
   if (pktlen < sizeof (struct GNUNET_TUN_TcpHeader))
   {
@@ -689,14 +905,14 @@ tcp_from_helper (const struct GNUNET_TUN_TcpHeader *tcp,
   }
   state = get_redirect_state (af, IPPROTO_TCP,
                              source_ip, 
-                             ntohs (tcp->spt),
+                             ntohs (tcp->source_port),
                              destination_ip,
-                             ntohs (tcp->dpt),
+                             ntohs (tcp->destination_port),
                              NULL);
   if (NULL == state)
   {
     GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-               _("Packet dropped, have no matching connection information\n"));
+               _("TCP Packet dropped, have no matching connection information\n"));
     
     return;
   }
@@ -704,13 +920,29 @@ tcp_from_helper (const struct GNUNET_TUN_TcpHeader *tcp,
      sender will need to lookup the correct values anyway */
   memcpy (buf, tcp, pktlen);  
   mtcp = (struct GNUNET_TUN_TcpHeader *) buf;
-  mtcp->spt = 0;
-  mtcp->dpt = 0;
+  mtcp->source_port = 0;
+  mtcp->destination_port = 0;
   mtcp->crc = 0;
+
+  mlen = sizeof (struct GNUNET_EXIT_TcpDataMessage) + (pktlen - sizeof (struct GNUNET_TUN_TcpHeader));
+  if (mlen >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
+  {
+    GNUNET_break (0);
+    return;
+  }
+
+  tnq = GNUNET_malloc (sizeof (struct TunnelMessageQueue) + mlen);
+  tnq->payload = &tnq[1];
+  tnq->len = mlen;
+  tdm = (struct GNUNET_EXIT_TcpDataMessage *) &tnq[1];
+  tdm->header.size = htons ((uint16_t) mlen);
+  tdm->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_TCP_DATA_TO_VPN);
+  tdm->reserved = htonl (0);
+  memcpy (&tdm->tcp_header,
+         buf, 
+         pktlen);
   send_packet_to_mesh_tunnel (state->tunnel,
-                             mtcp, pktlen,
-                             NULL,
-                             GNUNET_MESSAGE_TYPE_VPN_TCP_DATA);
+                             tnq);
 }
 
 
@@ -728,6 +960,10 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
   const struct GNUNET_TUN_Layer2PacketHeader *pkt_tun;
   size_t size;
 
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Got %u-byte message of type %u from gnunet-helper-exit\n",
+             ntohs (message->size),
+             ntohs (message->type));
   GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# Packets received from TUN"),
                            1, GNUNET_NO);
@@ -749,85 +985,101 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
   size -= sizeof (struct GNUNET_TUN_Layer2PacketHeader) + sizeof (struct GNUNET_MessageHeader);
   switch (ntohs (pkt_tun->proto))
   {
-  case ETH_P_IPV6:
+  case ETH_P_IPV4:
     {
-      const struct GNUNET_TUN_IPv6Header *pkt6;
+      const struct GNUNET_TUN_IPv4Header *pkt4;
 
-      if (size < sizeof (struct GNUNET_TUN_IPv6Header))
+      if (size < sizeof (struct GNUNET_TUN_IPv4Header))
       {
        /* Kernel to blame? */
        GNUNET_break (0);
        return;
       }
-      pkt6 = (struct GNUNET_TUN_IPv6Header *) &pkt_tun[1];
-      if (size != ntohs (pkt6->payload_length))
+      pkt4 = (const struct GNUNET_TUN_IPv4Header *) &pkt_tun[1];
+      if (size != ntohs (pkt4->total_length))
       {
        /* Kernel to blame? */
        GNUNET_break (0);
        return;
       }
-      size -= sizeof (struct GNUNET_TUN_IPv6Header);
-      switch (pkt6->next_header)
+      if (pkt4->header_length * 4 != sizeof (struct GNUNET_TUN_IPv4Header))
+      {
+       GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                   _("IPv4 packet options received.  Ignored.\n"));
+       return;
+      }
+      
+      size -= sizeof (struct GNUNET_TUN_IPv4Header);
+      switch (pkt4->protocol)
       {
       case IPPROTO_UDP:
-       udp_from_helper ((const struct GNUNET_TUN_UdpHeader *) &pkt6[1], size,
-                        AF_INET6,
-                        &pkt6->destination_address, 
-                        &pkt6->source_address);
+       udp_from_helper ((const struct GNUNET_TUN_UdpHeader *) &pkt4[1], size,
+                        AF_INET,
+                        &pkt4->destination_address, 
+                        &pkt4->source_address);
        break;
       case IPPROTO_TCP:
-       tcp_from_helper ((const struct GNUNET_TUN_TcpHeader *) &pkt6[1], size,
-                        AF_INET6,
-                        &pkt6->destination_address, 
-                        &pkt6->source_address);
+       tcp_from_helper ((const struct GNUNET_TUN_TcpHeader *) &pkt4[1], size,
+                        AF_INET,
+                        &pkt4->destination_address, 
+                        &pkt4->source_address);
+       break;
+      case IPPROTO_ICMP:
+       icmp_from_helper ((const struct GNUNET_TUN_IcmpHeader *) &pkt4[1], size,
+                         AF_INET,
+                         &pkt4->destination_address, 
+                         &pkt4->source_address);
        break;
       default:
        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                   _("IPv6 packet with unsupported next header received.  Ignored.\n"));
+                   _("IPv4 packet with unsupported next header %u received.  Ignored.\n"),
+                   (int) pkt4->protocol);
        return;
       }
     }
     break;
-  case ETH_P_IPV4:
+  case ETH_P_IPV6:
     {
-      const struct GNUNET_TUN_IPv4Header *pkt4;
+      const struct GNUNET_TUN_IPv6Header *pkt6;
 
-      if (size < sizeof (struct GNUNET_TUN_IPv4Header))
+      if (size < sizeof (struct GNUNET_TUN_IPv6Header))
       {
        /* Kernel to blame? */
        GNUNET_break (0);
        return;
       }
-      pkt4 = (const struct GNUNET_TUN_IPv4Header *) &pkt_tun[1];
-      if (size != ntohs (pkt4->total_length))
+      pkt6 = (struct GNUNET_TUN_IPv6Header *) &pkt_tun[1];
+      if (size != ntohs (pkt6->payload_length) + sizeof (struct GNUNET_TUN_IPv6Header))
       {
        /* Kernel to blame? */
        GNUNET_break (0);
        return;
       }
-      if (pkt4->header_length * 4 != sizeof (struct GNUNET_TUN_IPv4Header))
-      {
-       GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                   _("IPv4 packet options received.  Ignored.\n"));
-       return;
-      }
-      size -= sizeof (struct GNUNET_TUN_IPv4Header);
-      switch (pkt4->protocol)
+      size -= sizeof (struct GNUNET_TUN_IPv6Header);
+      switch (pkt6->next_header)
       {
       case IPPROTO_UDP:
-       udp_from_helper ((const struct GNUNET_TUN_UdpHeader *) &pkt4[1], size,
-                        AF_INET,
-                        &pkt4->destination_address, 
-                        &pkt4->source_address);
+       udp_from_helper ((const struct GNUNET_TUN_UdpHeader *) &pkt6[1], size,
+                        AF_INET6,
+                        &pkt6->destination_address, 
+                        &pkt6->source_address);
+       break;
       case IPPROTO_TCP:
-       tcp_from_helper ((const struct GNUNET_TUN_TcpHeader *) &pkt4[1], size,
-                        AF_INET,
-                        &pkt4->destination_address, 
-                        &pkt4->source_address);
+       tcp_from_helper ((const struct GNUNET_TUN_TcpHeader *) &pkt6[1], size,
+                        AF_INET6,
+                        &pkt6->destination_address, 
+                        &pkt6->source_address);
+       break;
+      case IPPROTO_ICMPV6:
+       icmp_from_helper ((const struct GNUNET_TUN_IcmpHeader *) &pkt6[1], size,
+                         AF_INET6,
+                         &pkt6->destination_address, 
+                         &pkt6->source_address);
        break;
       default:
        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                   _("IPv4 packet with unsupported next header received.  Ignored.\n"));
+                   _("IPv6 packet with unsupported next header %d received.  Ignored.\n"),
+                    pkt6->next_header);
        return;
       }
     }
@@ -858,21 +1110,23 @@ setup_fresh_address (int af,
   local_address->proto = (uint8_t) proto;
   /* default "local" port range is often 32768--61000,
      so we pick a random value in that range */         
-  local_address->port 
-    = (uint16_t) 32768 + GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
-                                                  28232);      
+  if ( ( (af == AF_INET) && (proto == IPPROTO_ICMP) ) ||
+       ( (af == AF_INET6) && (proto == IPPROTO_ICMPV6) ) )
+    local_address->port = 0;
+  else
+    local_address->port 
+      = (uint16_t) 32768 + GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
+                                                    28232);      
   switch (af)
   {
   case AF_INET:
     {
-      const char *ipv4addr = exit_argv[4];
-      const char *ipv4mask = exit_argv[5];
       struct in_addr addr;
       struct in_addr mask;
       struct in_addr rnd;
 
-      GNUNET_assert (1 == inet_pton (AF_INET, ipv4addr, &addr));
-      GNUNET_assert (1 == inet_pton (AF_INET, ipv4mask, &mask));           
+      addr = exit_ipv4addr;
+      mask = exit_ipv4mask;
       if (0 == ~mask.s_addr)
       {
        /* only one valid IP anyway */
@@ -895,13 +1149,12 @@ setup_fresh_address (int af,
     break;
   case AF_INET6:
     {
-      const char *ipv6addr = exit_argv[2];
       struct in6_addr addr;
       struct in6_addr mask;
       struct in6_addr rnd;
       int i;
-
-      GNUNET_assert (1 == inet_pton (AF_INET6, ipv6addr, &addr));
+      
+      addr = exit_ipv6addr;
       GNUNET_assert (ipv6prefix < 128);
       if (ipv6prefix == 127)
       {
@@ -912,7 +1165,7 @@ setup_fresh_address (int af,
       /* Given ABCD::/96, we want a mask of 'ABCD::FFFF:FFFF,
         thus: */
       mask = addr;
-      for (i=127;i>=128-ipv6prefix;i--)
+      for (i=127;i>=ipv6prefix;i--)
        mask.s6_addr[i / 8] |= (1 << (i % 8));
       
       /* Pick random IPv6 address within the subnet, except 'addr' or 'mask' itself */
@@ -970,9 +1223,14 @@ setup_state_record (struct TunnelState *state)
   /* generate fresh, unique address */
   do
   {
-    setup_fresh_address (state->serv->address.af,
-                        state->serv->address.proto,
-                        &state->ri.local_address);
+    if (NULL == state->serv)
+      setup_fresh_address (state->ri.remote_address.af,
+                          state->ri.remote_address.proto,
+                          &state->ri.local_address);
+    else
+      setup_fresh_address (state->serv->address.af,
+                          state->serv->address.proto,
+                          &state->ri.local_address);
   } while (NULL != get_redirect_state (state->ri.remote_address.af,
                                       state->ri.remote_address.proto,
                                       &state->ri.remote_address.address,
@@ -987,8 +1245,9 @@ setup_state_record (struct TunnelState *state)
                inet_ntop (state->ri.local_address.af, 
                           &state->ri.local_address.address,
                           buf, sizeof (buf)),
-               (unsigned int) state->ri.local_address.port);  
+               (unsigned int) state->ri.local_address.port);
   }
+  state->state_key = key;
   GNUNET_assert (GNUNET_OK ==
                 GNUNET_CONTAINER_multihashmap_put (connections_map, 
                                                    &key, state,
@@ -1022,9 +1281,10 @@ setup_state_record (struct TunnelState *state)
  *                TCP header, depending on protocol)
  * @param payload_length number of bytes in 'payload'
  * @param protocol IPPROTO_UDP or IPPROTO_TCP
+ * @param tcp_header skeleton of the TCP header, NULL for UDP
  * @param src_address source address to use (IP and port)
  * @param dst_address destination address to use (IP and port)
- * @param pkt6 where to write the assembled packet; must
+ * @param pkt4 where to write the assembled packet; must
  *        contain enough space for the IP header, UDP/TCP header
  *        AND the payload
  */
@@ -1069,8 +1329,8 @@ prepare_ipv4_packet (const void *payload, size_t payload_length,
     {
       struct GNUNET_TUN_UdpHeader *pkt4_udp = (struct GNUNET_TUN_UdpHeader *) &pkt4[1];
 
-      pkt4_udp->spt = htons (src_address->port);
-      pkt4_udp->dpt = htons (dst_address->port);
+      pkt4_udp->source_port = htons (src_address->port);
+      pkt4_udp->destination_port = htons (dst_address->port);
       pkt4_udp->len = htons ((uint16_t) payload_length);
       GNUNET_TUN_calculate_udp4_checksum (pkt4,
                                          pkt4_udp,
@@ -1082,9 +1342,9 @@ prepare_ipv4_packet (const void *payload, size_t payload_length,
     {
       struct GNUNET_TUN_TcpHeader *pkt4_tcp = (struct GNUNET_TUN_TcpHeader *) &pkt4[1];
       
-      memcpy (pkt4_tcp, tcp_header, sizeof (struct GNUNET_TUN_TcpHeader));
-      pkt4_tcp->spt = htons (src_address->port);
-      pkt4_tcp->dpt = htons (dst_address->port);
+      *pkt4_tcp = *tcp_header;
+      pkt4_tcp->source_port = htons (src_address->port);
+      pkt4_tcp->destination_port = htons (dst_address->port);
       GNUNET_TUN_calculate_tcp4_checksum (pkt4,
                                          pkt4_tcp,
                                          payload,
@@ -1109,6 +1369,7 @@ prepare_ipv4_packet (const void *payload, size_t payload_length,
  *                TCP header, depending on protocol)
  * @param payload_length number of bytes in 'payload'
  * @param protocol IPPROTO_UDP or IPPROTO_TCP
+ * @param tcp_header skeleton TCP header data to send, NULL for UDP
  * @param src_address source address to use (IP and port)
  * @param dst_address destination address to use (IP and port)
  * @param pkt6 where to write the assembled packet; must
@@ -1132,12 +1393,7 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
     len += sizeof (struct GNUNET_TUN_UdpHeader);
     break;
   case IPPROTO_TCP:
-    /* tcp_header (with port/crc not set) must be part of payload! */
-    if (len < sizeof (struct GNUNET_TUN_TcpHeader))
-    {
-      GNUNET_break (0);
-      return;
-    }
+    len += sizeof (struct GNUNET_TUN_TcpHeader);
     break;
   default:
     GNUNET_break (0);
@@ -1151,9 +1407,9 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
 
   GNUNET_TUN_initialize_ipv6_header (pkt6,
                                     protocol,
-                                    len,
-                                    &dst_address->address.ipv6,
-                                    &src_address->address.ipv6);
+                                    len,                                  
+                                    &src_address->address.ipv6,
+                                    &dst_address->address.ipv6);
 
   switch (protocol)
   {
@@ -1161,29 +1417,29 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
     {
       struct GNUNET_TUN_UdpHeader *pkt6_udp = (struct GNUNET_TUN_UdpHeader *) &pkt6[1];
 
-      pkt6_udp->spt = htons (src_address->port);
-      pkt6_udp->dpt = htons (dst_address->port);
+      pkt6_udp->source_port = htons (src_address->port);
+      pkt6_udp->destination_port = htons (dst_address->port);
       pkt6_udp->len = htons ((uint16_t) payload_length);
-      pkt6_udp->crc = 0;
       GNUNET_TUN_calculate_udp6_checksum (pkt6,
                                          pkt6_udp,
                                          payload,
                                          payload_length);
-      memcpy (&pkt6[1], payload, payload_length);
+      memcpy (&pkt6_udp[1], payload, payload_length);
     }
     break;
   case IPPROTO_TCP:
     {
-      struct GNUNET_TUN_TcpHeader *pkt6_tcp = (struct GNUNET_TUN_TcpHeader *) pkt6;
+      struct GNUNET_TUN_TcpHeader *pkt6_tcp = (struct GNUNET_TUN_TcpHeader *) &pkt6[1];
 
       /* memcpy first here as some TCP header fields are initialized this way! */
-      memcpy (pkt6_tcp, payload, payload_length);
-      pkt6_tcp->spt = htons (src_address->port);
-      pkt6_tcp->dpt = htons (dst_address->port);
+      *pkt6_tcp = *tcp_header;
+      pkt6_tcp->source_port = htons (src_address->port);
+      pkt6_tcp->destination_port = htons (dst_address->port);
       GNUNET_TUN_calculate_tcp6_checksum (pkt6,
                                          pkt6_tcp,
                                          payload,
                                          payload_length);
+      memcpy (&pkt6_tcp[1], payload, payload_length);
     }
     break;
   default:
@@ -1198,7 +1454,7 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
  *
  * @param destination_address IP and port to use for the TCP packet's destination
  * @param source_address IP and port to use for the TCP packet's source
- * @param tcp header template to use
+ * @param tcp_header header template to use
  * @param payload payload of the TCP packet
  * @param payload_length number of bytes in 'payload'
  */
@@ -1229,6 +1485,7 @@ send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
     GNUNET_break (0);
     return;
   }
+  len += sizeof (struct GNUNET_TUN_TcpHeader);
   len += payload_length;
   if (len >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
   {
@@ -1236,11 +1493,11 @@ send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
     return;
   }
   {
-    char buf[len];
+    char buf[len] GNUNET_ALIGN;
     struct GNUNET_MessageHeader *hdr;
     struct GNUNET_TUN_Layer2PacketHeader *tun;
     
-    hdr= (struct GNUNET_MessageHeader *) buf;
+    hdr = (struct GNUNET_MessageHeader *) buf;
     hdr->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
     hdr->size = htons (len);
     tun = (struct GNUNET_TUN_Layer2PacketHeader*) &hdr[1];
@@ -1299,7 +1556,7 @@ send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
  *         GNUNET_SYSERR to close it (signal serious error)
  */
 static int
-receive_tcp_service (void *unused GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
+receive_tcp_service (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                      void **tunnel_ctx GNUNET_UNUSED,
                      const struct GNUNET_PeerIdentity *sender GNUNET_UNUSED,
                      const struct GNUNET_MessageHeader *message,
@@ -1330,20 +1587,25 @@ receive_tcp_service (void *unused GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunn
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
   }
+  if (start->tcp_header.off * 4 < sizeof (struct GNUNET_TUN_TcpHeader))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
   GNUNET_break_op (ntohl (start->reserved) == 0);
   /* setup fresh connection */
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received data from %s for forwarding to TCP service %s on port %u\n",
              GNUNET_i2s (sender),
              GNUNET_h2s (&start->service_descriptor),
-             (unsigned int) ntohs (start->tcp_header.dpt));  
+             (unsigned int) ntohs (start->tcp_header.destination_port));  
   if (NULL == (state->serv = find_service (tcp_services, &start->service_descriptor, 
-                                          ntohs (start->tcp_header.dpt))))
+                                          ntohs (start->tcp_header.destination_port))))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_INFO, 
                _("No service found for %s on port %d!\n"),
                "TCP",
-               ntohs (start->tcp_header.dpt));
+               ntohs (start->tcp_header.destination_port));
     GNUNET_STATISTICS_update (stats,
                              gettext_noop ("# TCP requests dropped (no such service)"),
                              1, GNUNET_NO);
@@ -1406,6 +1668,11 @@ receive_tcp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
     GNUNET_break_op (0);
     return GNUNET_SYSERR;
   }
+  if (start->tcp_header.off * 4 < sizeof (struct GNUNET_TUN_TcpHeader))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
   af = (int) ntohl (start->af);
   state->ri.remote_address.af = af;
   switch (af)
@@ -1439,7 +1706,7 @@ receive_tcp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
     }
     v6 = (const struct in6_addr*) &start[1];
     payload = &v6[1];
-    pkt_len -= sizeof (struct in_addr);
+    pkt_len -= sizeof (struct in6_addr);
     state->ri.remote_address.address.ipv6 = *v6;
     break;
   default:
@@ -1454,11 +1721,10 @@ receive_tcp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                inet_ntop (af, 
                           &state->ri.remote_address.address,
                           buf, sizeof (buf)),
-               (unsigned int) ntohs (start->tcp_header.dpt));  
+               (unsigned int) ntohs (start->tcp_header.destination_port));  
   }
-
   state->ri.remote_address.proto = IPPROTO_TCP;
-  state->ri.remote_address.port = ntohs (start->tcp_header.dpt);
+  state->ri.remote_address.port = ntohs (start->tcp_header.destination_port);
   setup_state_record (state);
   send_tcp_packet_via_tun (&state->ri.remote_address,
                           &state->ri.local_address,
@@ -1514,11 +1780,18 @@ receive_tcp_data (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                              1, GNUNET_NO);
     return GNUNET_SYSERR;
   }
+  if (data->tcp_header.off * 4 < sizeof (struct GNUNET_TUN_TcpHeader))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
   GNUNET_break_op (ntohl (data->reserved) == 0);
   {
     char buf[INET6_ADDRSTRLEN];
     GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-               "Received additional data from %s for TCP stream to %s:%u\n",
+               "Received additional %u bytes of data from %s for TCP stream to %s:%u\n",
+               pkt_len,
                GNUNET_i2s (sender),
                inet_ntop (state->ri.remote_address.af, 
                           &state->ri.remote_address.address,
@@ -1535,28 +1808,31 @@ receive_tcp_data (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
 
 
 /**
- * Send a UDP packet via the TUN interface.
+ * Send an ICMP packet via the TUN interface.
  *
- * @param destination_address IP and port to use for the UDP packet's destination
- * @param source_address IP and port to use for the UDP packet's source
- * @param payload payload of the UDP packet (does NOT include UDP header)
+ * @param destination_address IP to use for the ICMP packet's destination
+ * @param source_address IP to use for the ICMP packet's source
+ * @param icmp_header ICMP header to send
+ * @param payload payload of the ICMP packet (does NOT include ICMP header)
  * @param payload_length number of bytes of data in payload
  */
 static void
-send_udp_packet_via_tun (const struct SocketAddress *destination_address,
-                        const struct SocketAddress *source_address,
-                        const void *payload, size_t payload_length)
+send_icmp_packet_via_tun (const struct SocketAddress *destination_address,
+                         const struct SocketAddress *source_address,
+                         const struct GNUNET_TUN_IcmpHeader *icmp_header,
+                         const void *payload, size_t payload_length)
 {
   size_t len;
+  struct GNUNET_TUN_IcmpHeader *icmp;
 
   GNUNET_STATISTICS_update (stats,
-                           gettext_noop ("# UDP packets sent via TUN"),
+                           gettext_noop ("# ICMP packets sent via TUN"),
                            1, GNUNET_NO);
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-             "Sending packet with %u bytes UDP payload via TUN\n",
+             "Sending packet with %u bytes ICMP payload via TUN\n",
              (unsigned int) payload_length);
   len = sizeof (struct GNUNET_MessageHeader) + sizeof (struct GNUNET_TUN_Layer2PacketHeader);
-  switch (source_address->af)
+  switch (destination_address->af)
   {
   case AF_INET:
     len += sizeof (struct GNUNET_TUN_IPv4Header);
@@ -1568,7 +1844,7 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
     GNUNET_break (0);
     return;
   }
-  len += sizeof (struct GNUNET_TUN_UdpHeader);
+  len += sizeof (struct GNUNET_TUN_IcmpHeader);
   len += payload_length;
   if (len >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
   {
@@ -1576,7 +1852,7 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
     return;
   }
   {
-    char buf[len];
+    char buf[len] GNUNET_ALIGN;
     struct GNUNET_MessageHeader *hdr;
     struct GNUNET_TUN_Layer2PacketHeader *tun;
     
@@ -1592,12 +1868,12 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
        struct GNUNET_TUN_IPv4Header * ipv4 = (struct GNUNET_TUN_IPv4Header*) &tun[1];
        
        tun->proto = htons (ETH_P_IPV4);
-       prepare_ipv4_packet (payload, payload_length,
-                            IPPROTO_UDP,
-                            NULL,
-                            source_address,
-                            destination_address,
-                            ipv4);
+       GNUNET_TUN_initialize_ipv4_header (ipv4,
+                                          IPPROTO_ICMP,
+                                          sizeof (struct GNUNET_TUN_IcmpHeader) + payload_length,
+                                          &source_address->address.ipv4,
+                                          &destination_address->address.ipv4);
+       icmp = (struct GNUNET_TUN_IcmpHeader*) &ipv4[1];
       }
       break;
     case AF_INET6:
@@ -1605,18 +1881,25 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
        struct GNUNET_TUN_IPv6Header * ipv6 = (struct GNUNET_TUN_IPv6Header*) &tun[1];
        
        tun->proto = htons (ETH_P_IPV6);
-       prepare_ipv6_packet (payload, payload_length, 
-                            IPPROTO_UDP,
-                            NULL,
-                            source_address,
-                            destination_address,
-                            ipv6);
+       GNUNET_TUN_initialize_ipv6_header (ipv6,
+                                          IPPROTO_ICMPV6,
+                                          sizeof (struct GNUNET_TUN_IcmpHeader) + payload_length,
+                                          &source_address->address.ipv6,
+                                          &destination_address->address.ipv6);
+       icmp = (struct GNUNET_TUN_IcmpHeader*) &ipv6[1];
       }
       break;   
     default:
       GNUNET_assert (0);
       break;
     }
+    *icmp = *icmp_header;
+    memcpy (&icmp[1],
+           payload,
+           payload_length);
+    GNUNET_TUN_calculate_icmp_checksum (icmp,
+                                       payload,
+                                       payload_length);
     (void) GNUNET_HELPER_send (helper_handle,
                               (const struct GNUNET_MessageHeader*) buf,
                               GNUNET_YES,
@@ -1626,15 +1909,591 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
 
 
 /**
- * Process a request to forward UDP data to the Internet via this peer.
+ * Synthesize a plausible ICMP payload for an ICMPv4 error
+ * response on the given tunnel.
  *
- * @param cls closure, NULL
- * @param tunnel connection to the other end
- * @param tunnel_ctx pointer to our 'struct TunnelState *'
- * @param sender who sent the message
- * @param message the actual message
- * @param atsi performance data for the connection
- * @return GNUNET_OK to keep the connection open,
+ * @param state tunnel information
+ * @param ipp IPv6 header to fill in (ICMP payload)
+ * @param udp "UDP" header to fill in (ICMP payload); might actually
+ *            also be the first 8 bytes of the TCP header
+ */
+static void
+make_up_icmpv4_payload (struct TunnelState *state,
+                       struct GNUNET_TUN_IPv4Header *ipp,
+                       struct GNUNET_TUN_UdpHeader *udp)
+{
+  GNUNET_TUN_initialize_ipv4_header (ipp,
+                                    state->ri.remote_address.proto,
+                                    sizeof (struct GNUNET_TUN_TcpHeader),
+                                    &state->ri.remote_address.address.ipv4,
+                                    &state->ri.local_address.address.ipv4);
+  udp->source_port = htons (state->ri.remote_address.port);
+  udp->destination_port = htons (state->ri.local_address.port);
+  udp->len = htons (0);
+  udp->crc = htons (0);
+}
+
+
+/**
+ * Synthesize a plausible ICMP payload for an ICMPv6 error
+ * response on the given tunnel.
+ *
+ * @param state tunnel information
+ * @param ipp IPv6 header to fill in (ICMP payload)
+ * @param udp "UDP" header to fill in (ICMP payload); might actually
+ *            also be the first 8 bytes of the TCP header
+ */
+static void
+make_up_icmpv6_payload (struct TunnelState *state,
+                       struct GNUNET_TUN_IPv6Header *ipp,
+                       struct GNUNET_TUN_UdpHeader *udp)
+{
+  GNUNET_TUN_initialize_ipv6_header (ipp,
+                                    state->ri.remote_address.proto,
+                                    sizeof (struct GNUNET_TUN_TcpHeader),
+                                    &state->ri.remote_address.address.ipv6,
+                                    &state->ri.local_address.address.ipv6);
+  udp->source_port = htons (state->ri.remote_address.port);
+  udp->destination_port = htons (state->ri.local_address.port);
+  udp->len = htons (0);
+  udp->crc = htons (0);
+}
+
+
+/**
+ * Process a request to forward ICMP data to the Internet via this peer.
+ *
+ * @param cls closure, NULL
+ * @param tunnel connection to the other end
+ * @param tunnel_ctx pointer to our 'struct TunnelState *'
+ * @param sender who sent the message
+ * @param message the actual message
+ * @param atsi performance data for the connection
+ * @return GNUNET_OK to keep the connection open,
+ *         GNUNET_SYSERR to close it (signal serious error)
+ */
+static int
+receive_icmp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
+                    void **tunnel_ctx GNUNET_UNUSED,
+                    const struct GNUNET_PeerIdentity *sender GNUNET_UNUSED,
+                    const struct GNUNET_MessageHeader *message,
+                    const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
+{
+  struct TunnelState *state = *tunnel_ctx;
+  const struct GNUNET_EXIT_IcmpInternetMessage *msg;
+  uint16_t pkt_len = ntohs (message->size);
+  const struct in_addr *v4;
+  const struct in6_addr *v6;  
+  const void *payload;
+  char buf[sizeof (struct GNUNET_TUN_IPv6Header) + 8] GNUNET_ALIGN;
+  int af;
+
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# ICMP IP-exit requests received via mesh"),
+                           1, GNUNET_NO);
+  if (pkt_len < sizeof (struct GNUNET_EXIT_IcmpInternetMessage))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  msg = (const struct GNUNET_EXIT_IcmpInternetMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_IcmpInternetMessage);  
+
+  af = (int) ntohl (msg->af);
+  if ( (NULL != state->heap_node) &&
+       (af != state->ri.remote_address.af) )
+  {
+    /* other peer switched AF on this tunnel; not allowed */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  switch (af)
+  {
+  case AF_INET:
+    if (pkt_len < sizeof (struct in_addr))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    if (! ipv4_exit)
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    v4 = (const struct in_addr*) &msg[1];
+    payload = &v4[1];
+    pkt_len -= sizeof (struct in_addr);
+    state->ri.remote_address.address.ipv4 = *v4;
+    if (NULL == state->heap_node)
+    {
+      state->ri.remote_address.af = af;
+      state->ri.remote_address.proto = IPPROTO_ICMP;
+      setup_state_record (state);
+    }
+    /* check that ICMP type is something we want to support 
+       and possibly make up payload! */
+    switch (msg->icmp_header.type)
+    {
+    case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
+    case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
+      break;
+    case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
+    case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
+    case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      /* make up payload */
+      {
+       struct GNUNET_TUN_IPv4Header *ipp = (struct GNUNET_TUN_IPv4Header *) buf;
+       struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+
+       GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+       pkt_len = sizeof (struct GNUNET_TUN_IPv4Header) + 8;
+       make_up_icmpv4_payload (state, 
+                               ipp,
+                               udp);
+       payload = ipp;
+      }
+      break;
+    default:
+      GNUNET_break_op (0);
+      GNUNET_STATISTICS_update (stats,
+                               gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
+                               1, GNUNET_NO);
+      return GNUNET_SYSERR;      
+    }
+    /* end AF_INET */
+    break;
+  case AF_INET6:
+    if (pkt_len < sizeof (struct in6_addr))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    if (! ipv6_exit)
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    v6 = (const struct in6_addr*) &msg[1];
+    payload = &v6[1];
+    pkt_len -= sizeof (struct in6_addr);
+    state->ri.remote_address.address.ipv6 = *v6;
+    if (NULL == state->heap_node)
+    {
+      state->ri.remote_address.af = af;
+      state->ri.remote_address.proto = IPPROTO_ICMPV6;
+      setup_state_record (state);
+    }
+    /* check that ICMP type is something we want to support 
+       and possibly make up payload! */
+    switch (msg->icmp_header.type)
+    {
+    case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
+    case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
+      break;
+    case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
+    case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
+    case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
+    case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      /* make up payload */
+      {
+       struct GNUNET_TUN_IPv6Header *ipp = (struct GNUNET_TUN_IPv6Header *) buf;
+       struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+
+       GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+       pkt_len = sizeof (struct GNUNET_TUN_IPv6Header) + 8;
+       make_up_icmpv6_payload (state, 
+                               ipp,
+                               udp);
+       payload = ipp;
+      }
+      break;
+    default:
+      GNUNET_break_op (0);
+      GNUNET_STATISTICS_update (stats,
+                               gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
+                               1, GNUNET_NO);
+      return GNUNET_SYSERR;      
+    }
+    /* end AF_INET6 */
+    break;    
+  default:
+    /* bad AF */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  {
+    char buf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Received ICMP data from %s for forwarding to %s\n",
+               GNUNET_i2s (sender),
+               inet_ntop (af, 
+                          &state->ri.remote_address.address,
+                          buf, sizeof (buf)));
+  }
+  send_icmp_packet_via_tun (&state->ri.remote_address,
+                           &state->ri.local_address,
+                           &msg->icmp_header,
+                           payload, pkt_len);
+  return GNUNET_YES;
+}
+
+
+/**
+ * Setup ICMP payload for ICMP error messages. Called
+ * for both IPv4 and IPv6 addresses.
+ *
+ * @param state context for creating the IP Packet
+ * @param buf where to create the payload, has at least
+ *       sizeof (struct GNUNET_TUN_IPv6Header) + 8 bytes
+ * @return number of bytes of payload we created in buf
+ */
+static uint16_t
+make_up_icmp_service_payload (struct TunnelState *state,
+                             char *buf)
+{
+  switch (state->serv->address.af)
+  {
+  case AF_INET:
+    {
+      struct GNUNET_TUN_IPv4Header *ipv4;
+      struct GNUNET_TUN_UdpHeader *udp;
+      
+      ipv4 = (struct GNUNET_TUN_IPv4Header *)buf;
+      udp = (struct GNUNET_TUN_UdpHeader *) &ipv4[1];
+      make_up_icmpv4_payload (state,
+                             ipv4,
+                             udp);
+      GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+      return sizeof (struct GNUNET_TUN_IPv4Header) + 8;
+    }
+    break;
+  case AF_INET6:
+    {
+      struct GNUNET_TUN_IPv6Header *ipv6;
+      struct GNUNET_TUN_UdpHeader *udp;
+
+      ipv6 = (struct GNUNET_TUN_IPv6Header *)buf;
+      udp = (struct GNUNET_TUN_UdpHeader *) &ipv6[1];
+      make_up_icmpv6_payload (state,
+                             ipv6,
+                             udp);
+      GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+      return sizeof (struct GNUNET_TUN_IPv6Header) + 8;      
+    }
+    break;
+  default:
+    GNUNET_break (0);
+  }
+  return 0;
+}
+
+
+/**
+ * Process a request via mesh to send ICMP data to a service
+ * offered by this system.
+ *
+ * @param cls closure, NULL
+ * @param tunnel connection to the other end
+ * @param tunnel_ctx pointer to our 'struct TunnelState *'
+ * @param sender who sent the message
+ * @param message the actual message
+ * @param atsi performance data for the connection
+ * @return GNUNET_OK to keep the connection open,
+ *         GNUNET_SYSERR to close it (signal serious error)
+ */
+static int
+receive_icmp_service (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
+                     void **tunnel_ctx,
+                     const struct GNUNET_PeerIdentity *sender GNUNET_UNUSED,
+                     const struct GNUNET_MessageHeader *message,
+                     const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
+{
+  struct TunnelState *state = *tunnel_ctx;
+  const struct GNUNET_EXIT_IcmpServiceMessage *msg;
+  uint16_t pkt_len = ntohs (message->size);
+  struct GNUNET_TUN_IcmpHeader icmp;
+  char buf[sizeof (struct GNUNET_TUN_IPv6Header) + 8] GNUNET_ALIGN;
+  const void *payload;
+
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# ICMP service requests received via mesh"),
+                           1, GNUNET_NO);
+  /* check that we got at least a valid header */
+  if (pkt_len < sizeof (struct GNUNET_EXIT_IcmpServiceMessage))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  msg = (const struct GNUNET_EXIT_IcmpServiceMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_IcmpServiceMessage);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Received data from %s for forwarding to ICMP service %s\n",
+             GNUNET_i2s (sender),
+             GNUNET_h2s (&msg->service_descriptor));
+  if (NULL == state->serv)
+  {
+    /* first packet to service must not be ICMP (cannot determine service!) */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  icmp = msg->icmp_header;
+  payload = &msg[1];
+  state->ri.remote_address = state->serv->address;    
+  setup_state_record (state);
+
+  /* check that ICMP type is something we want to support,
+     perform ICMP PT if needed ans possibly make up payload */
+  switch (msg->af)
+  {
+  case AF_INET:
+    switch (msg->icmp_header.type)
+    {
+    case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
+      if (state->serv->address.af == AF_INET6)
+       icmp.type = GNUNET_TUN_ICMPTYPE6_ECHO_REPLY;
+      break;
+    case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
+      if (state->serv->address.af == AF_INET6)
+       icmp.type = GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST;
+      break;
+    case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
+      if (state->serv->address.af == AF_INET6)
+       icmp.type = GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE;
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      payload = buf;
+      pkt_len = make_up_icmp_service_payload (state, buf);
+      break;
+    case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:
+      if (state->serv->address.af == AF_INET6)
+       icmp.type = GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED;
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      payload = buf;
+      pkt_len = make_up_icmp_service_payload (state, buf);
+      break;
+    case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
+      if (state->serv->address.af == AF_INET6)
+      {
+       GNUNET_STATISTICS_update (stats,
+                                 gettext_noop ("# ICMPv4 packets dropped (impossible PT to v6)"),
+                                 1, GNUNET_NO);
+       return GNUNET_OK;
+      }
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      payload = buf;
+      pkt_len = make_up_icmp_service_payload (state, buf);
+      break;
+    default:
+      GNUNET_break_op (0);
+      GNUNET_STATISTICS_update (stats,
+                               gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
+                               1, GNUNET_NO);
+      return GNUNET_SYSERR;
+    }
+    /* end of AF_INET */
+    break;
+  case AF_INET6:
+    switch (msg->icmp_header.type)
+    {
+    case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
+      if (state->serv->address.af == AF_INET)
+       icmp.type = GNUNET_TUN_ICMPTYPE_ECHO_REPLY;
+      break;
+    case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
+      if (state->serv->address.af == AF_INET)
+       icmp.type = GNUNET_TUN_ICMPTYPE_ECHO_REQUEST;
+      break;
+    case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
+      if (state->serv->address.af == AF_INET)
+       icmp.type = GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE;
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      payload = buf;
+      pkt_len = make_up_icmp_service_payload (state, buf);
+      break;
+    case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
+      if (state->serv->address.af == AF_INET)
+       icmp.type = GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED;
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      payload = buf;
+      pkt_len = make_up_icmp_service_payload (state, buf);
+      break;
+    case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
+    case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
+      if (state->serv->address.af == AF_INET)
+      {
+       GNUNET_STATISTICS_update (stats,
+                                 gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
+                                 1, GNUNET_NO);
+       return GNUNET_OK;
+      }
+      if (0 != pkt_len)
+      {
+       GNUNET_break_op (0);
+       return GNUNET_SYSERR;
+      }
+      payload = buf;
+      pkt_len = make_up_icmp_service_payload (state, buf);
+      break;
+    default:
+      GNUNET_break_op (0);
+      GNUNET_STATISTICS_update (stats,
+                               gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
+                               1, GNUNET_NO);
+      return GNUNET_SYSERR;
+    }
+    /* end of AF_INET6 */
+    break;
+  default:
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  send_icmp_packet_via_tun (&state->ri.remote_address,
+                           &state->ri.local_address,
+                           &icmp,
+                           payload, pkt_len);
+  return GNUNET_YES;
+}
+
+
+/**
+ * Send a UDP packet via the TUN interface.
+ *
+ * @param destination_address IP and port to use for the UDP packet's destination
+ * @param source_address IP and port to use for the UDP packet's source
+ * @param payload payload of the UDP packet (does NOT include UDP header)
+ * @param payload_length number of bytes of data in payload
+ */
+static void
+send_udp_packet_via_tun (const struct SocketAddress *destination_address,
+                        const struct SocketAddress *source_address,
+                        const void *payload, size_t payload_length)
+{
+  size_t len;
+
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# UDP packets sent via TUN"),
+                           1, GNUNET_NO);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Sending packet with %u bytes UDP payload via TUN\n",
+             (unsigned int) payload_length);
+  len = sizeof (struct GNUNET_MessageHeader) + sizeof (struct GNUNET_TUN_Layer2PacketHeader);
+  switch (source_address->af)
+  {
+  case AF_INET:
+    len += sizeof (struct GNUNET_TUN_IPv4Header);
+    break;
+  case AF_INET6:
+    len += sizeof (struct GNUNET_TUN_IPv6Header);
+    break;
+  default:
+    GNUNET_break (0);
+    return;
+  }
+  len += sizeof (struct GNUNET_TUN_UdpHeader);
+  len += payload_length;
+  if (len >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
+  {
+    GNUNET_break (0);
+    return;
+  }
+  {
+    char buf[len] GNUNET_ALIGN;
+    struct GNUNET_MessageHeader *hdr;
+    struct GNUNET_TUN_Layer2PacketHeader *tun;
+    
+    hdr= (struct GNUNET_MessageHeader *) buf;
+    hdr->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
+    hdr->size = htons (len);
+    tun = (struct GNUNET_TUN_Layer2PacketHeader*) &hdr[1];
+    tun->flags = htons (0);
+    switch (source_address->af)
+    {
+    case AF_INET:
+      {
+       struct GNUNET_TUN_IPv4Header * ipv4 = (struct GNUNET_TUN_IPv4Header*) &tun[1];
+       
+       tun->proto = htons (ETH_P_IPV4);
+       prepare_ipv4_packet (payload, payload_length,
+                            IPPROTO_UDP,
+                            NULL,
+                            source_address,
+                            destination_address,
+                            ipv4);
+      }
+      break;
+    case AF_INET6:
+      {
+       struct GNUNET_TUN_IPv6Header * ipv6 = (struct GNUNET_TUN_IPv6Header*) &tun[1];
+       
+       tun->proto = htons (ETH_P_IPV6);
+       prepare_ipv6_packet (payload, payload_length, 
+                            IPPROTO_UDP,
+                            NULL,
+                            source_address,
+                            destination_address,
+                            ipv6);
+      }
+      break;   
+    default:
+      GNUNET_assert (0);
+      break;
+    }
+    (void) GNUNET_HELPER_send (helper_handle,
+                              (const struct GNUNET_MessageHeader*) buf,
+                              GNUNET_YES,
+                              NULL, NULL);
+  }
+}
+
+
+/**
+ * Process a request to forward UDP data to the Internet via this peer.
+ *
+ * @param cls closure, NULL
+ * @param tunnel connection to the other end
+ * @param tunnel_ctx pointer to our 'struct TunnelState *'
+ * @param sender who sent the message
+ * @param message the actual message
+ * @param atsi performance data for the connection
+ * @return GNUNET_OK to keep the connection open,
  *         GNUNET_SYSERR to close it (signal serious error)
  */
 static int
@@ -1698,7 +2557,7 @@ receive_udp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
     }
     v6 = (const struct in6_addr*) &msg[1];
     payload = &v6[1];
-    pkt_len -= sizeof (struct in_addr);
+    pkt_len -= sizeof (struct in6_addr);
     state->ri.remote_address.address.ipv6 = *v6;
     break;
   default:
@@ -1806,7 +2665,7 @@ receive_udp_service (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
 static void *
 new_tunnel (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
             const struct GNUNET_PeerIdentity *initiator GNUNET_UNUSED,
-            const struct GNUNET_ATS_Information *ats GNUNET_UNUSED)
+            const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
 {
   struct TunnelState *s = GNUNET_malloc (sizeof (struct TunnelState));
 
@@ -1926,10 +2785,10 @@ cleanup (void *cls GNUNET_UNUSED,
   }
   if (stats != NULL)
   {
-    GNUNET_STATISTICS_destroy (stats, GNUNET_YES);
+    GNUNET_STATISTICS_destroy (stats, GNUNET_NO);
     stats = NULL;
   }
-  for (i=0;i<5;i++)
+  for (i=0;i<8;i++)
     GNUNET_free_non_null (exit_argv[i]);
 }
 
@@ -2103,6 +2962,31 @@ read_service_conf (void *cls GNUNET_UNUSED, const char *section)
 }
 
 
+/**
+ * Test if the given AF is supported by this system.
+ * 
+ * @param af to test
+ * @return GNUNET_OK if the AF is supported
+ */
+static int
+test_af (int af)
+{
+  int s;
+
+  s = socket (af, SOCK_STREAM, 0);
+  if (-1 == s)
+  {
+    if (EAFNOSUPPORT == errno)
+      return GNUNET_NO;
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR,
+                        "socket");
+    return GNUNET_SYSERR;
+  }
+  close (s);
+  return GNUNET_OK;
+}
+
+
 /**
  * @brief Main function that will be run by the scheduler.
  *
@@ -2117,11 +3001,13 @@ run (void *cls, char *const *args GNUNET_UNUSED,
      const struct GNUNET_CONFIGURATION_Handle *cfg_)
 {
   static struct GNUNET_MESH_MessageHandler handlers[] = {
+    {&receive_icmp_service, GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_SERVICE, 0},
+    {&receive_icmp_remote, GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_INTERNET, 0},
     {&receive_udp_service, GNUNET_MESSAGE_TYPE_VPN_UDP_TO_SERVICE, 0},
     {&receive_udp_remote, GNUNET_MESSAGE_TYPE_VPN_UDP_TO_INTERNET, 0},
     {&receive_tcp_service, GNUNET_MESSAGE_TYPE_VPN_TCP_TO_SERVICE_START, 0},
     {&receive_tcp_remote, GNUNET_MESSAGE_TYPE_VPN_TCP_TO_INTERNET_START, 0},
-    {&receive_tcp_data, GNUNET_MESSAGE_TYPE_VPN_TCP_DATA, 0},
+    {&receive_tcp_data, GNUNET_MESSAGE_TYPE_VPN_TCP_DATA_TO_EXIT, 0},
     {NULL, 0, 0}
   };
 
@@ -2137,15 +3023,39 @@ run (void *cls, char *const *args GNUNET_UNUSED,
   char *ipv6prefix_s;
   char *ipv4addr;
   char *ipv4mask;
-  struct in_addr v4;
-  struct in6_addr v6;
 
+  if (GNUNET_YES !=
+      GNUNET_OS_check_helper_binary ("gnunet-helper-exit"))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+               _("`%s' must be installed SUID, refusing to run\n"),
+               "gnunet-helper-exit");
+    global_ret = 1;
+    return;
+  }
   cfg = cfg_;
   stats = GNUNET_STATISTICS_create ("exit", cfg);
   ipv4_exit = GNUNET_CONFIGURATION_get_value_yesno (cfg, "exit", "EXIT_IPV4");
   ipv6_exit = GNUNET_CONFIGURATION_get_value_yesno (cfg, "exit", "EXIT_IPV6"); 
   ipv4_enabled = GNUNET_CONFIGURATION_get_value_yesno (cfg, "exit", "ENABLE_IPV4");
   ipv6_enabled = GNUNET_CONFIGURATION_get_value_yesno (cfg, "exit", "ENABLE_IPV6"); 
+
+  if ( (ipv4_exit || ipv4_enabled) &&
+       GNUNET_OK != test_af (AF_INET))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+               _("This system does not support IPv4, will disable IPv4 functions despite them being enabled in the configuration\n"));
+    ipv4_exit = GNUNET_NO;
+    ipv4_enabled = GNUNET_NO;
+  }
+  if ( (ipv6_exit || ipv6_enabled) &&
+       GNUNET_OK != test_af (AF_INET6))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+               _("This system does not support IPv6, will disable IPv6 functions despite them being enabled in the configuration\n"));
+    ipv6_exit = GNUNET_NO;
+    ipv6_enabled = GNUNET_NO;
+  }
   if (ipv4_exit && (! ipv4_enabled))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
@@ -2209,12 +3119,14 @@ run (void *cls, char *const *args GNUNET_UNUSED,
   {
     exit_argv[2] = GNUNET_strdup ("%");
   }
+  
+
   if (GNUNET_YES == ipv6_enabled)
   {
     if ( (GNUNET_SYSERR ==
          GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV6ADDR",
                                                 &ipv6addr) ||
-         (1 != inet_pton (AF_INET6, ipv6addr, &v6))) )
+         (1 != inet_pton (AF_INET6, ipv6addr, &exit_ipv6addr))) )
     {
       GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "No valid entry 'IPV6ADDR' in configuration!\n");
@@ -2253,7 +3165,7 @@ run (void *cls, char *const *args GNUNET_UNUSED,
     if ( (GNUNET_SYSERR ==
          GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV4ADDR",
                                                 &ipv4addr) ||
-         (1 != inet_pton (AF_INET, ipv4addr, &v4))) )
+         (1 != inet_pton (AF_INET, ipv4addr, &exit_ipv4addr))) )
       {
        GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                    "No valid entry for 'IPV4ADDR' in configuration!\n");
@@ -2264,7 +3176,7 @@ run (void *cls, char *const *args GNUNET_UNUSED,
     if ( (GNUNET_SYSERR ==
          GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV4MASK",
                                                 &ipv4mask) ||
-         (1 != inet_pton (AF_INET, ipv4mask, &v4))) )
+         (1 != inet_pton (AF_INET, ipv4mask, &exit_ipv4mask))) )
     {
       GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "No valid entry 'IPV4MASK' in configuration!\n");
@@ -2321,7 +3233,7 @@ main (int argc, char *const *argv)
           GNUNET_PROGRAM_run (argc, argv, "gnunet-daemon-exit",
                               gettext_noop
                               ("Daemon to run to provide an IP exit node for the VPN"),
-                              options, &run, NULL)) ? 0 : 1;
+                              options, &run, NULL)) ? global_ret : 1;
 }