-bugfixes, code cleanup
[oweals/gnunet.git] / src / vpn / gnunet-service-vpn.c
index 7aeabf457cfdc4ccee325515991d23475d4c7bbd..abdc16d79a6f1f622f78141e03de1588b318ca88 100644 (file)
  *        IP traffic received on those IPs via the GNUnet mesh 
  * @author Philipp Toelke
  * @author Christian Grothoff
- *
- * TODO:
- * Basics:
- * - test!
- *
- * Features:
- * - add back ICMP support (especially needed for IPv6)
- *
- * Code cleanup:
- * - consider moving IP-header building / checksumming code into shared library
- *   with dns/exit/vpn (libgnunettun_tcpip?)
  */
 #include "platform.h"
 #include "gnunet_util_lib.h"
@@ -73,7 +62,7 @@ struct DestinationEntry
    * Key under which this entry is in the 'destination_map' (only valid
    * if 'heap_node != NULL').
    */
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
 
   /**
    * Pre-allocated tunnel for this destination, or NULL for none.
@@ -102,7 +91,7 @@ struct DestinationEntry
       /**
        * The description of the service (only used for service tunnels).
        */
-      GNUNET_HashCode service_descriptor;
+      struct GNUNET_HashCode service_descriptor;
 
       /**
        * Peer offering the service.
@@ -295,6 +284,11 @@ struct TunnelState
 };
 
 
+/**
+ * Return value from 'main'.
+ */
+static int global_ret;
+
 /**
  * Configuration we use.
  */
@@ -377,7 +371,7 @@ static unsigned long long max_tunnel_mappings;
 static void
 get_destination_key_from_ip (int af,
                             const void *address,
-                            GNUNET_HashCode *key)
+                            struct GNUNET_HashCode *key)
 {
   switch (af)
   {
@@ -417,11 +411,11 @@ get_tunnel_key_from_ips (int af,
                         uint16_t source_port,
                         const void *destination_ip,
                         uint16_t destination_port,
-                        GNUNET_HashCode *key)
+                        struct GNUNET_HashCode *key)
 {
   char *off;
 
-  memset (key, 0, sizeof (GNUNET_HashCode));
+  memset (key, 0, sizeof (struct GNUNET_HashCode));
   /* the GNUnet hashmap only uses the first sizeof(unsigned int) of the hash,
      so we put the ports in there (and hope for few collisions) */
   off = (char*) key;
@@ -466,7 +460,7 @@ send_client_reply (struct GNUNET_SERVER_Client *client,
                   int result_af,
                   const void *addr)
 {
-  char buf[sizeof (struct RedirectToIpResponseMessage) + sizeof (struct in6_addr)];
+  char buf[sizeof (struct RedirectToIpResponseMessage) + sizeof (struct in6_addr)] GNUNET_ALIGN;
   struct RedirectToIpResponseMessage *res;
   size_t rlen;
 
@@ -507,7 +501,7 @@ send_client_reply (struct GNUNET_SERVER_Client *client,
 static void
 free_tunnel_state (struct TunnelState *ts)
 {
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
   struct TunnelMessageQueueEntry *tnq;
   struct GNUNET_MESH_Tunnel *tunnel;
 
@@ -516,11 +510,6 @@ free_tunnel_state (struct TunnelState *ts)
   GNUNET_STATISTICS_update (stats,
                            gettext_noop ("# Active tunnels"),
                            -1, GNUNET_NO);
-  if (GNUNET_SCHEDULER_NO_TASK != ts->destroy_task)
-  {
-    GNUNET_SCHEDULER_cancel (ts->destroy_task);
-    ts->destroy_task = GNUNET_SCHEDULER_NO_TASK;
-  }
   while (NULL != (tnq = ts->tmq_head))
   {
     GNUNET_CONTAINER_DLL_remove (ts->tmq_head,
@@ -546,6 +535,11 @@ free_tunnel_state (struct TunnelState *ts)
     ts->tunnel = NULL;
     GNUNET_MESH_tunnel_destroy (tunnel);
   }
+  if (GNUNET_SCHEDULER_NO_TASK != ts->destroy_task)
+  {
+    GNUNET_SCHEDULER_cancel (ts->destroy_task);
+    ts->destroy_task = GNUNET_SCHEDULER_NO_TASK;
+  }
   if (NULL != ts->heap_node)
   {
     GNUNET_CONTAINER_heap_remove_node (ts->heap_node);
@@ -576,7 +570,7 @@ free_tunnel_state (struct TunnelState *ts)
  * Destroy the mesh tunnel.
  *
  * @param cls the 'struct TunnelState' with the tunnel to destroy
- * @param ts schedule context
+ * @param tc scheduler context
  */
 static void
 destroy_tunnel_task (void *cls,
@@ -611,7 +605,7 @@ tunnel_peer_disconnect_handler (void *cls,
              "Peer %s disconnected from tunnel.\n",
              GNUNET_i2s (peer));
   GNUNET_STATISTICS_update (stats,
-                           gettext_noop ("# Peers connected to mesh tunnels"),
+                           gettext_noop ("# peers connected to mesh tunnels"),
                            -1, GNUNET_NO);
   if (NULL != ts->th)
   {
@@ -648,7 +642,7 @@ tunnel_peer_connect_handler (void *cls,
              "Peer %s connected to tunnel.\n",
              GNUNET_i2s (peer));
   GNUNET_STATISTICS_update (stats,
-                           gettext_noop ("# Peers connected to mesh tunnels"),
+                           gettext_noop ("# peers connected to mesh tunnels"),
                            1, GNUNET_NO);
   if (NULL == ts->client)
     return; /* nothing to do */
@@ -695,7 +689,6 @@ send_to_peer_notify_callback (void *cls, size_t size, void *buf)
   if (NULL != (tnq = ts->tmq_head))
     ts->th = GNUNET_MESH_notify_transmit_ready (ts->tunnel, 
                                                GNUNET_NO /* cork */, 
-                                               42 /* priority */,
                                                GNUNET_TIME_UNIT_FOREVER_REL,
                                                NULL, 
                                                tnq->len,
@@ -736,6 +729,7 @@ send_to_tunnel (struct TunnelMessageQueueEntry *tnq,
     GNUNET_CONTAINER_DLL_remove (ts->tmq_head,
                                 ts->tmq_tail,
                                 dq);
+    ts->tmq_length--;
     GNUNET_MESH_notify_transmit_ready_cancel (ts->th);
     ts->th = NULL;
     GNUNET_STATISTICS_update (stats,
@@ -747,7 +741,6 @@ send_to_tunnel (struct TunnelMessageQueueEntry *tnq,
   if (NULL == ts->th)
     ts->th = GNUNET_MESH_notify_transmit_ready (ts->tunnel, 
                                                GNUNET_NO /* cork */,
-                                               42 /* priority */,
                                                GNUNET_TIME_UNIT_FOREVER_REL,
                                                NULL, 
                                                tnq->len,
@@ -761,12 +754,14 @@ send_to_tunnel (struct TunnelMessageQueueEntry *tnq,
  *
  * @param de destination entry for which we need to setup a tunnel
  * @param client client to notify on successful tunnel setup, or NULL for none
+ * @param client_af address family of the address returned to the client
  * @param request_id request ID to send in client notification (unused if client is NULL)
  * @return tunnel state of the tunnel that was created
  */
 static struct TunnelState *
 create_tunnel_to_destination (struct DestinationEntry *de,
                              struct GNUNET_SERVER_Client *client,
+                             int client_af,
                              uint64_t request_id)
 {
   struct TunnelState *ts;
@@ -776,6 +771,7 @@ create_tunnel_to_destination (struct DestinationEntry *de,
                            1, GNUNET_NO);
   GNUNET_assert (NULL == de->ts);
   ts = GNUNET_malloc (sizeof (struct TunnelState));
+  ts->af = client_af;
   if (NULL != client)
   {
     ts->request_id = request_id;
@@ -786,7 +782,6 @@ create_tunnel_to_destination (struct DestinationEntry *de,
   ts->destination.heap_node = NULL; /* copy is NOT in destination heap */
   de->ts = ts;
   ts->destination_container = de; /* we are referenced from de */
-  ts->af = AF_UNSPEC; /* so far, unknown */
   ts->tunnel = GNUNET_MESH_tunnel_create (mesh_handle,
                                          ts,
                                          &tunnel_peer_connect_handler,
@@ -848,6 +843,7 @@ expire_tunnel (struct TunnelState *except)
   struct TunnelState *ts;
 
   ts = GNUNET_CONTAINER_heap_peek (tunnel_heap);
+  GNUNET_assert (NULL != ts);
   if (except == ts)
     return; /* can't do this */
   free_tunnel_state (ts);
@@ -859,7 +855,7 @@ expire_tunnel (struct TunnelState *except)
  *
  * @param destination description of the destination
  * @param af address family on this end (AF_INET or AF_INET6)
- * @param protocol IPPROTO_TCP or IPPROTO_UDP
+ * @param protocol IPPROTO_TCP or IPPROTO_UDP or IPPROTO_ICMP or IPPROTO_ICMPV6
  * @param source_ip source IP used by the sender (struct in_addr or struct in6_addr)
  * @param destination_ip destination IP used by the sender (struct in_addr or struct in6_addr)
  * @param payload payload of the packet after the IP header
@@ -874,7 +870,7 @@ route_packet (struct DestinationEntry *destination,
              const void *payload,
              size_t payload_length)
 {
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
   struct TunnelState *ts;
   struct TunnelMessageQueueEntry *tnq;
   size_t alen;
@@ -882,8 +878,9 @@ route_packet (struct DestinationEntry *destination,
   int is_new;
   const struct GNUNET_TUN_UdpHeader *udp;
   const struct GNUNET_TUN_TcpHeader *tcp;
-  uint16_t spt;
-  uint16_t dpt;
+  const struct GNUNET_TUN_IcmpHeader *icmp;
+  uint16_t source_port;
+  uint16_t destination_port;
 
   switch (protocol)
   {
@@ -895,15 +892,22 @@ route_packet (struct DestinationEntry *destination,
        GNUNET_break (0);
        return;
       }
+      tcp = NULL; /* make compiler happy */
+      icmp = NULL;  /* make compiler happy */
       udp = payload;
-      spt = ntohs (udp->spt);
-      dpt = ntohs (udp->dpt);
+      if (udp->len < sizeof (struct GNUNET_TUN_UdpHeader))
+      {
+       GNUNET_break_op (0);
+       return;
+      }
+      source_port = ntohs (udp->source_port);
+      destination_port = ntohs (udp->destination_port);
       get_tunnel_key_from_ips (af,
                               IPPROTO_UDP,
                               source_ip,
-                              spt,
+                              source_port,
                               destination_ip,
-                              dpt,
+                              destination_port,
                               &key);
     }
     break;
@@ -914,16 +918,51 @@ route_packet (struct DestinationEntry *destination,
        /* blame kernel? */
        GNUNET_break (0);
        return;
-      }
+      }      
+      udp = NULL; /* make compiler happy */
+      icmp = NULL;  /* make compiler happy */
       tcp = payload;
-      spt = ntohs (tcp->spt);
-      dpt = ntohs (tcp->dpt);
+      if (tcp->off * 4 < sizeof (struct GNUNET_TUN_TcpHeader))
+      {
+       GNUNET_break_op (0);
+       return;
+      }
+      source_port = ntohs (tcp->source_port);
+      destination_port = ntohs (tcp->destination_port);
       get_tunnel_key_from_ips (af,
                               IPPROTO_TCP,
                               source_ip,
-                              spt,
+                              source_port,
+                              destination_ip,
+                              destination_port,
+                              &key);
+    }
+    break;
+  case IPPROTO_ICMP:  
+  case IPPROTO_ICMPV6:  
+    {
+      if ( (AF_INET == af) ^ (protocol == IPPROTO_ICMP) )
+      {
+       GNUNET_break (0);
+       return;
+      }
+      if (payload_length < sizeof (struct GNUNET_TUN_IcmpHeader))
+      {
+       /* blame kernel? */
+       GNUNET_break (0);
+       return;
+      }
+      tcp = NULL; /* make compiler happy */
+      udp = NULL;  /* make compiler happy */
+      icmp = payload;
+      source_port = 0;
+      destination_port = 0;
+      get_tunnel_key_from_ips (af,
+                              protocol,
+                              source_ip,
+                              0,
                               destination_ip,
-                              dpt,
+                              0,
                               &key);
     }
     break;
@@ -957,13 +996,13 @@ route_packet (struct DestinationEntry *destination,
                  "Routing %s packet from %s:%u -> %s:%u to destination %s:%u\n",
                  (protocol == IPPROTO_TCP) ? "TCP" : "UDP",
                  inet_ntop (af, source_ip, sbuf, sizeof (sbuf)),
-                 spt,
+                 source_port,
                  inet_ntop (af, destination_ip, dbuf, sizeof (dbuf)),
-                 dpt,
+                 destination_port,
                  inet_ntop (destination->details.exit_destination.af,
                             &destination->details.exit_destination.ip,
                             xbuf, sizeof (xbuf)),
-                 dpt);
+                 destination_port);
     }
   }
   else
@@ -978,9 +1017,9 @@ route_packet (struct DestinationEntry *destination,
                  "Routing %s packet from %s:%u -> %s:%u to service %s at peer %s\n",
                  (protocol == IPPROTO_TCP) ? "TCP" : "UDP",
                  inet_ntop (af, source_ip, sbuf, sizeof (sbuf)),
-                 spt,
+                 source_port,
                  inet_ntop (af, destination_ip, dbuf, sizeof (dbuf)),
-                 dpt,
+                 destination_port,
                  GNUNET_h2s (&destination->details.service_destination.service_descriptor),
                  GNUNET_i2s (&destination->details.service_destination.target));
     }
@@ -996,7 +1035,7 @@ route_packet (struct DestinationEntry *destination,
        available) or create a fresh one */
     is_new = GNUNET_YES;
     if (NULL == destination->ts)
-      ts = create_tunnel_to_destination (destination, NULL, 0);
+      ts = create_tunnel_to_destination (destination, NULL, af, 0);
     else
       ts = destination->ts;
     if (NULL == ts)
@@ -1016,8 +1055,8 @@ route_packet (struct DestinationEntry *destination,
       ts->source_ip.v6 = * (const struct in6_addr *) source_ip;
       ts->destination_ip.v6 = * (const struct in6_addr *) destination_ip;
     }
-    ts->source_port = spt;
-    ts->destination_port = dpt;
+    ts->source_port = source_port;
+    ts->destination_port = destination_port;
     ts->heap_node = GNUNET_CONTAINER_heap_insert (tunnel_heap,
                                                  ts,
                                                  GNUNET_TIME_absolute_get ().abs_value);
@@ -1064,8 +1103,8 @@ route_packet (struct DestinationEntry *destination,
       usm->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_UDP_TO_SERVICE);
       /* if the source port is below 32000, we assume it has a special
         meaning; if not, we pick a random port (this is a heuristic) */
-      usm->source_port = (ntohs (udp->spt) < 32000) ? udp->spt : 0;
-      usm->destination_port = udp->dpt;
+      usm->source_port = (ntohs (udp->source_port) < 32000) ? udp->source_port : 0;
+      usm->destination_port = udp->destination_port;
       usm->service_descriptor = destination->details.service_destination.service_descriptor;
       memcpy (&usm[1],
              &udp[1],
@@ -1093,8 +1132,8 @@ route_packet (struct DestinationEntry *destination,
       uim->header.size = htons ((uint16_t) mlen);
       uim->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_UDP_TO_INTERNET); 
       uim->af = htonl (destination->details.exit_destination.af);
-      uim->source_port = (ntohs (udp->spt) < 32000) ? udp->spt : 0;
-      uim->destination_port = udp->dpt;
+      uim->source_port = (ntohs (udp->source_port) < 32000) ? udp->source_port : 0;
+      uim->destination_port = udp->destination_port;
       switch (destination->details.exit_destination.af)
       {
       case AF_INET:
@@ -1189,7 +1228,7 @@ route_packet (struct DestinationEntry *destination,
       struct GNUNET_EXIT_TcpDataMessage *tdm;
 
       mlen = sizeof (struct GNUNET_EXIT_TcpDataMessage) + 
-       alen + payload_length - sizeof (struct GNUNET_TUN_TcpHeader);
+       payload_length - sizeof (struct GNUNET_TUN_TcpHeader);
       if (mlen >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
       {
        GNUNET_break (0);
@@ -1200,7 +1239,7 @@ route_packet (struct DestinationEntry *destination,
       tnq->msg = &tnq[1];
       tdm = (struct  GNUNET_EXIT_TcpDataMessage *) &tnq[1];
       tdm->header.size = htons ((uint16_t) mlen);
-      tdm->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_TCP_DATA);
+      tdm->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_TCP_DATA_TO_EXIT);
       tdm->reserved = htonl (0);
       tdm->tcp_header = *tcp;
       memcpy (&tdm[1],
@@ -1208,6 +1247,242 @@ route_packet (struct DestinationEntry *destination,
              payload_length - sizeof (struct GNUNET_TUN_TcpHeader));
      }
     break;
+  case IPPROTO_ICMP:
+  case IPPROTO_ICMPV6:
+    if (destination->is_service)
+    {
+      struct GNUNET_EXIT_IcmpServiceMessage *ism;
+
+      mlen = sizeof (struct GNUNET_EXIT_IcmpServiceMessage) + 
+       payload_length - sizeof (struct GNUNET_TUN_IcmpHeader);
+      if (mlen >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
+      {
+       GNUNET_break (0);
+       return;
+      }
+      tnq = GNUNET_malloc (sizeof (struct TunnelMessageQueueEntry) + mlen);
+      tnq->msg = &tnq[1];
+      ism = (struct GNUNET_EXIT_IcmpServiceMessage *) &tnq[1];
+      ism->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_SERVICE);
+      ism->af = htonl (af); /* need to tell destination ICMP protocol family! */
+      ism->service_descriptor = destination->details.service_destination.service_descriptor;
+      ism->icmp_header = *icmp;
+      /* ICMP protocol translation will be done by the receiver (as we don't know
+        the target AF); however, we still need to possibly discard the payload
+        depending on the ICMP type */
+      switch (af)
+      {
+      case AF_INET:
+       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:
+         /* throw away ICMP payload, won't be useful for the other side anyway */
+         payload_length = sizeof (struct GNUNET_TUN_IcmpHeader); 
+         break;
+       default:
+         GNUNET_STATISTICS_update (stats,
+                                   gettext_noop ("# ICMPv4 packets dropped (not allowed)"),
+                                   1, GNUNET_NO);
+         return;
+       }
+       /* end of AF_INET */
+       break;
+      case AF_INET6:
+       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:
+         /* throw away ICMP payload, won't be useful for the other side anyway */
+         payload_length = 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 (not allowed)"),
+                                   1, GNUNET_NO);
+         return;
+       }       
+       /* end of AF_INET6 */
+       break;
+      default:
+       GNUNET_assert (0);
+       break;
+      }
+
+      /* update length calculations, as payload_length may have changed */
+      mlen = sizeof (struct GNUNET_EXIT_IcmpServiceMessage) + 
+       alen + payload_length - sizeof (struct GNUNET_TUN_IcmpHeader);      
+      tnq->len = mlen;
+      ism->header.size = htons ((uint16_t) mlen);
+      /* finally, copy payload (if there is any left...) */
+      memcpy (&ism[1],
+             &icmp[1],
+             payload_length - sizeof (struct GNUNET_TUN_IcmpHeader));
+    }
+    else
+    {
+      struct GNUNET_EXIT_IcmpInternetMessage *iim;
+      struct in_addr *ip4dst;
+      struct in6_addr *ip6dst;
+      void *payload;
+
+      mlen = sizeof (struct GNUNET_EXIT_IcmpInternetMessage) + 
+       alen + payload_length - sizeof (struct GNUNET_TUN_IcmpHeader);
+      if (mlen >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
+      {
+       GNUNET_break (0);
+       return;
+      }
+      tnq = GNUNET_malloc (sizeof (struct TunnelMessageQueueEntry) + 
+                          mlen);
+      tnq->msg = &tnq[1];
+      iim = (struct GNUNET_EXIT_IcmpInternetMessage *) &tnq[1];
+      iim->header.type = htons (GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_INTERNET); 
+      iim->icmp_header = *icmp;
+      /* Perform ICMP protocol-translation (depending on destination AF and source AF)
+        and throw away ICMP payload depending on ICMP message type */
+      switch (af)
+      {
+      case AF_INET:
+       switch (icmp->type)
+       {
+       case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:      
+         if (destination->details.exit_destination.af == AF_INET6)
+           iim->icmp_header.type = GNUNET_TUN_ICMPTYPE6_ECHO_REPLY;
+         break;
+       case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:    
+         if (destination->details.exit_destination.af == AF_INET6)
+           iim->icmp_header.type = GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST;
+         break;
+       case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
+         if (destination->details.exit_destination.af == AF_INET6)
+           iim->icmp_header.type = GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE;
+         /* throw away IP-payload, exit will have to make it up anyway */
+         payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+         break;
+       case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED: 
+         if (destination->details.exit_destination.af == AF_INET6)
+           iim->icmp_header.type = GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED;
+         /* throw away IP-payload, exit will have to make it up anyway */
+         payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+         break;
+       case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
+         if (destination->details.exit_destination.af == AF_INET6)
+           {
+             GNUNET_STATISTICS_update (stats,
+                                       gettext_noop ("# ICMPv4 packets dropped (impossible PT to v6)"),
+                                       1, GNUNET_NO);
+             GNUNET_free (tnq);
+             return;
+           }
+         /* throw away IP-payload, exit will have to make it up anyway */
+         payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+         break;
+       default:
+         GNUNET_STATISTICS_update (stats,
+                                   gettext_noop ("# ICMPv4 packets dropped (type not allowed)"),
+                                   1, GNUNET_NO);
+         GNUNET_free (tnq);        
+         return;
+       }
+       /* end of AF_INET */
+       break;
+      case AF_INET6:
+       switch (icmp->type)
+         {
+         case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
+           if (destination->details.exit_destination.af == AF_INET6)
+             iim->icmp_header.type = GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE;
+           /* throw away IP-payload, exit will have to make it up anyway */
+           payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+           break;
+         case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
+           if (destination->details.exit_destination.af == AF_INET)
+             iim->icmp_header.type = GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED;
+           /* throw away IP-payload, exit will have to make it up anyway */
+           payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+           break;
+         case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
+           if (destination->details.exit_destination.af == AF_INET)
+           {
+             GNUNET_STATISTICS_update (stats,
+                                       gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
+                                       1, GNUNET_NO);
+             GNUNET_free (tnq);
+             return;
+           }
+           /* throw away IP-payload, exit will have to make it up anyway */
+           payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+           break;
+         case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
+           if (destination->details.exit_destination.af == AF_INET)
+           {
+             GNUNET_STATISTICS_update (stats,
+                                       gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
+                                       1, GNUNET_NO);
+             GNUNET_free (tnq);
+             return;
+           }
+           /* throw away IP-payload, exit will have to make it up anyway */
+           payload_length = sizeof (struct GNUNET_TUN_IcmpHeader);
+           break;
+         case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
+           if (destination->details.exit_destination.af == AF_INET)
+             iim->icmp_header.type = GNUNET_TUN_ICMPTYPE_ECHO_REQUEST;
+           break;
+         case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
+           if (destination->details.exit_destination.af == AF_INET)
+             iim->icmp_header.type = GNUNET_TUN_ICMPTYPE_ECHO_REPLY;
+           break;
+         default:
+           GNUNET_STATISTICS_update (stats,
+                                     gettext_noop ("# ICMPv6 packets dropped (type not allowed)"),
+                                     1, GNUNET_NO);
+           GNUNET_free (tnq);      
+           return;
+         }
+       /* end of AF_INET6 */
+       break;
+      default:
+       GNUNET_assert (0);
+      } 
+      /* update length calculations, as payload_length may have changed */
+      mlen = sizeof (struct GNUNET_EXIT_IcmpInternetMessage) + 
+       alen + payload_length - sizeof (struct GNUNET_TUN_IcmpHeader);      
+      tnq->len = mlen;
+      iim->header.size = htons ((uint16_t) mlen);
+
+      /* need to tell destination ICMP protocol family! */
+      iim->af = htonl (destination->details.exit_destination.af);
+      switch (destination->details.exit_destination.af)
+      {
+      case AF_INET:
+       ip4dst = (struct in_addr *) &iim[1];
+       *ip4dst = destination->details.exit_destination.ip.v4;
+       payload = &ip4dst[1];
+       break;
+      case AF_INET6:
+       ip6dst = (struct in6_addr *) &iim[1];
+       *ip6dst = destination->details.exit_destination.ip.v6;
+       payload = &ip6dst[1];
+       break;
+      default:
+       GNUNET_assert (0);
+      }
+      memcpy (payload,
+             &icmp[1],
+             payload_length - sizeof (struct GNUNET_TUN_IcmpHeader));
+    }
+    break;
   default:
     /* not supported above, how can we get here !? */
     GNUNET_assert (0);
@@ -1227,13 +1502,13 @@ route_packet (struct DestinationEntry *destination,
  * @param client NULL
  * @param message message we got from the client (VPN tunnel interface)
  */
-static void
+static int
 message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
                const struct GNUNET_MessageHeader *message)
 {
   const struct GNUNET_TUN_Layer2PacketHeader *tun;
   size_t mlen;
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
   struct DestinationEntry *de;
 
   GNUNET_STATISTICS_update (stats,
@@ -1244,7 +1519,7 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
        (mlen < sizeof (struct GNUNET_MessageHeader) + sizeof (struct GNUNET_TUN_Layer2PacketHeader)) )
   {
     GNUNET_break (0);
-    return;
+    return GNUNET_OK;
   }
   tun = (const struct GNUNET_TUN_Layer2PacketHeader *) &message[1];
   mlen -= (sizeof (struct GNUNET_MessageHeader) + sizeof (struct GNUNET_TUN_Layer2PacketHeader));
@@ -1258,7 +1533,7 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
       {
        /* blame kernel */
        GNUNET_break (0);
-       return;
+        return GNUNET_OK;
       }
       pkt6 = (const struct GNUNET_TUN_IPv6Header *) &tun[1];
       get_destination_key_from_ip (AF_INET6,
@@ -1280,7 +1555,7 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
                               &pkt6->destination_address,
                               buf,
                               sizeof (buf)));
-       return;
+       return GNUNET_OK;
       }
       route_packet (de,
                    AF_INET6,
@@ -1299,7 +1574,7 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
       {
        /* blame kernel */
        GNUNET_break (0);
-       return;
+       return GNUNET_OK;
       }
       pkt4 = (struct GNUNET_TUN_IPv4Header *) &tun[1];
       get_destination_key_from_ip (AF_INET,
@@ -1321,13 +1596,13 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
                               &pkt4->destination_address,
                               buf,
                               sizeof (buf)));
-       return;
+        return GNUNET_OK;
       }
       if (pkt4->header_length * 4 != sizeof (struct GNUNET_TUN_IPv4Header))
       {
        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                    _("Received IPv4 packet with options (dropping it)\n"));                
-       return;
+        return GNUNET_OK;
       }
       route_packet (de,
                    AF_INET,
@@ -1344,6 +1619,400 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
                (unsigned int) ntohs (tun->proto));
     break;
   }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Synthesize a plausible ICMP payload for an ICMP error
+ * response on the given tunnel.
+ *
+ * @param ts tunnel information
+ * @param ipp IPv4 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 *ts,
+                       struct GNUNET_TUN_IPv4Header *ipp,
+                       struct GNUNET_TUN_UdpHeader *udp)
+{
+  GNUNET_TUN_initialize_ipv4_header (ipp,
+                                    ts->protocol,
+                                    sizeof (struct GNUNET_TUN_TcpHeader),
+                                    &ts->source_ip.v4,
+                                    &ts->destination_ip.v4);
+  udp->source_port = htons (ts->source_port);
+  udp->destination_port = htons (ts->destination_port);
+  udp->len = htons (0);
+  udp->crc = htons (0);
+}
+
+
+/**
+ * Synthesize a plausible ICMP payload for an ICMP error
+ * response on the given tunnel.
+ *
+ * @param ts 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 *ts,
+                       struct GNUNET_TUN_IPv6Header *ipp,
+                       struct GNUNET_TUN_UdpHeader *udp)
+{
+  GNUNET_TUN_initialize_ipv6_header (ipp,
+                                    ts->protocol,
+                                    sizeof (struct GNUNET_TUN_TcpHeader),
+                                    &ts->source_ip.v6,
+                                    &ts->destination_ip.v6);
+  udp->source_port = htons (ts->source_port);
+  udp->destination_port = htons (ts->destination_port);
+  udp->len = htons (0);
+  udp->crc = htons (0);
+}
+
+
+/**
+ * We got an ICMP packet back from the MESH tunnel.  Pass it on to the
+ * local virtual interface via the helper.
+ *
+ * @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_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
+                  void **tunnel_ctx, const struct GNUNET_PeerIdentity *sender,
+                  const struct GNUNET_MessageHeader *message,
+                  const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
+{
+  struct TunnelState *ts = *tunnel_ctx;
+  const struct GNUNET_EXIT_IcmpToVPNMessage *i2v;
+  size_t mlen;
+
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# ICMP packets received from mesh"),
+                           1, GNUNET_NO);
+  mlen = ntohs (message->size);
+  if (mlen < sizeof (struct GNUNET_EXIT_IcmpToVPNMessage))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (NULL == ts->heap_node)
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (AF_UNSPEC == ts->af)
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  i2v = (const struct GNUNET_EXIT_IcmpToVPNMessage *) message;
+  mlen -= sizeof (struct GNUNET_EXIT_IcmpToVPNMessage);
+  {
+    char sbuf[INET6_ADDRSTRLEN];
+    char dbuf[INET6_ADDRSTRLEN];
+    
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Received ICMP packet from mesh, sending %u bytes from %s -> %s via TUN\n",
+               (unsigned int) mlen,
+               inet_ntop (ts->af, &ts->destination_ip, sbuf, sizeof (sbuf)),
+               inet_ntop (ts->af, &ts->source_ip, dbuf, sizeof (dbuf)));
+  }
+  switch (ts->af)
+  {
+  case AF_INET:
+    {
+      size_t size = sizeof (struct GNUNET_TUN_IPv4Header) 
+       + sizeof (struct GNUNET_TUN_IcmpHeader) 
+       + sizeof (struct GNUNET_MessageHeader) +
+       sizeof (struct GNUNET_TUN_Layer2PacketHeader) +
+       mlen;
+      {
+       /* reserve some extra space in case we have an ICMP type here where
+          we will need to make up the payload ourselves */
+       char buf[size + sizeof (struct GNUNET_TUN_IPv4Header) + 8] GNUNET_ALIGN;
+       struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
+       struct GNUNET_TUN_Layer2PacketHeader *tun = (struct GNUNET_TUN_Layer2PacketHeader*) &msg[1];
+       struct GNUNET_TUN_IPv4Header *ipv4 = (struct GNUNET_TUN_IPv4Header *) &tun[1];
+       struct GNUNET_TUN_IcmpHeader *icmp = (struct GNUNET_TUN_IcmpHeader *) &ipv4[1];
+       msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
+       tun->flags = htons (0);
+       tun->proto = htons (ETH_P_IPV4);
+       GNUNET_TUN_initialize_ipv4_header (ipv4,
+                                          IPPROTO_ICMP,
+                                          sizeof (struct GNUNET_TUN_IcmpHeader) + mlen,
+                                          &ts->destination_ip.v4,
+                                          &ts->source_ip.v4);
+       *icmp = i2v->icmp_header;
+       memcpy (&icmp[1],
+               &i2v[1],
+               mlen);
+       /* For some ICMP types, we need to adjust (make up) the payload here. 
+          Also, depending on the AF used on the other side, we have to 
+          do ICMP PT (translate ICMP types) */
+       switch (ntohl (i2v->af))
+       {
+       case AF_INET:     
+         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:         
+           {
+             struct GNUNET_TUN_IPv4Header *ipp = (struct GNUNET_TUN_IPv4Header *) &icmp[1];
+             struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+             
+             if (mlen != 0)
+               {
+                 /* sender did not strip ICMP payload? */
+                 GNUNET_break_op (0);
+                 return GNUNET_SYSERR;
+               }
+             size += sizeof (struct GNUNET_TUN_IPv4Header) + 8;
+             GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+             make_up_icmpv4_payload (ts, ipp, udp);
+           }
+           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:
+         /* ICMP PT 6-to-4 and possibly making up payloads */
+         switch (icmp->type)
+         {
+         case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
+           icmp->type = GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE;
+           {
+             struct GNUNET_TUN_IPv4Header *ipp = (struct GNUNET_TUN_IPv4Header *) &icmp[1];
+             struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+             
+             if (mlen != 0)
+               {
+                 /* sender did not strip ICMP payload? */
+                 GNUNET_break_op (0);
+                 return GNUNET_SYSERR;
+               }
+             size += sizeof (struct GNUNET_TUN_IPv4Header) + 8;
+             GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+             make_up_icmpv4_payload (ts, ipp, udp);
+           }
+           break;
+         case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
+           icmp->type = GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED;
+           {
+             struct GNUNET_TUN_IPv4Header *ipp = (struct GNUNET_TUN_IPv4Header *) &icmp[1];
+             struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+             
+             if (mlen != 0)
+               {
+                 /* sender did not strip ICMP payload? */
+                 GNUNET_break_op (0);
+                 return GNUNET_SYSERR;
+               }
+             size += sizeof (struct GNUNET_TUN_IPv4Header) + 8;
+             GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+             make_up_icmpv4_payload (ts, ipp, udp);
+           }
+           break;
+         case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
+         case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
+           GNUNET_STATISTICS_update (stats,
+                                     gettext_noop ("# ICMPv6 packets dropped (impossible PT to v4)"),
+                                     1, GNUNET_NO);
+           return GNUNET_OK;
+         case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
+           icmp->type = GNUNET_TUN_ICMPTYPE_ECHO_REQUEST;
+           break;
+         case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
+           icmp->type = GNUNET_TUN_ICMPTYPE_ECHO_REPLY;
+           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:
+         GNUNET_break_op (0);
+         return GNUNET_SYSERR;
+       }       
+       msg->size = htons (size);
+       GNUNET_TUN_calculate_icmp_checksum (icmp,
+                                           &i2v[1],
+                                           mlen);
+       (void) GNUNET_HELPER_send (helper_handle,
+                                  msg,
+                                  GNUNET_YES,
+                                  NULL, NULL);
+      }
+    }
+    break;
+  case AF_INET6:
+    {
+      size_t size = sizeof (struct GNUNET_TUN_IPv6Header) 
+       + sizeof (struct GNUNET_TUN_IcmpHeader) 
+       + sizeof (struct GNUNET_MessageHeader) +
+       sizeof (struct GNUNET_TUN_Layer2PacketHeader) +
+       mlen;
+      {
+       char buf[size + sizeof (struct GNUNET_TUN_IPv6Header) + 8] GNUNET_ALIGN;
+       struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
+       struct GNUNET_TUN_Layer2PacketHeader *tun = (struct GNUNET_TUN_Layer2PacketHeader*) &msg[1];
+       struct GNUNET_TUN_IPv6Header *ipv6 = (struct GNUNET_TUN_IPv6Header *) &tun[1];
+       struct GNUNET_TUN_IcmpHeader *icmp = (struct GNUNET_TUN_IcmpHeader *) &ipv6[1];
+       msg->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
+       tun->flags = htons (0);
+       tun->proto = htons (ETH_P_IPV6);
+       GNUNET_TUN_initialize_ipv6_header (ipv6,
+                                          IPPROTO_ICMPV6,
+                                          sizeof (struct GNUNET_TUN_IcmpHeader) + mlen,
+                                          &ts->destination_ip.v6,
+                                          &ts->source_ip.v6);
+       *icmp = i2v->icmp_header;
+       memcpy (&icmp[1],
+               &i2v[1],
+               mlen);
+
+       /* For some ICMP types, we need to adjust (make up) the payload here. 
+          Also, depending on the AF used on the other side, we have to 
+          do ICMP PT (translate ICMP types) */
+       switch (ntohl (i2v->af))
+       {
+       case AF_INET:     
+         /* ICMP PT 4-to-6 and possibly making up payloads */
+         switch (icmp->type)
+         {
+         case GNUNET_TUN_ICMPTYPE_ECHO_REPLY:
+           icmp->type = GNUNET_TUN_ICMPTYPE6_ECHO_REPLY;
+           break;
+         case GNUNET_TUN_ICMPTYPE_ECHO_REQUEST:
+           icmp->type = GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST;
+           break;
+         case GNUNET_TUN_ICMPTYPE_DESTINATION_UNREACHABLE:
+           icmp->type = GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE;
+           {
+             struct GNUNET_TUN_IPv6Header *ipp = (struct GNUNET_TUN_IPv6Header *) &icmp[1];
+             struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+             
+             if (mlen != 0)
+               {
+                 /* sender did not strip ICMP payload? */
+                 GNUNET_break_op (0);
+                 return GNUNET_SYSERR;
+               }
+             size += sizeof (struct GNUNET_TUN_IPv6Header) + 8;
+             GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+             make_up_icmpv6_payload (ts, ipp, udp);
+           }
+           break;
+         case GNUNET_TUN_ICMPTYPE_TIME_EXCEEDED:         
+           icmp->type = GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED;
+           {
+             struct GNUNET_TUN_IPv6Header *ipp = (struct GNUNET_TUN_IPv6Header *) &icmp[1];
+             struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+             
+             if (mlen != 0)
+               {
+                 /* sender did not strip ICMP payload? */
+                 GNUNET_break_op (0);
+                 return GNUNET_SYSERR;
+               }
+             size += sizeof (struct GNUNET_TUN_IPv6Header) + 8;
+             GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+             make_up_icmpv6_payload (ts, ipp, udp);
+           }
+           break;
+         case GNUNET_TUN_ICMPTYPE_SOURCE_QUENCH:
+           GNUNET_STATISTICS_update (stats,
+                                     gettext_noop ("# ICMPv4 packets dropped (impossible PT to v6)"),
+                                     1, GNUNET_NO);        
+           return GNUNET_OK;
+         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:
+         switch (icmp->type)
+         {
+         case GNUNET_TUN_ICMPTYPE6_DESTINATION_UNREACHABLE:
+         case GNUNET_TUN_ICMPTYPE6_TIME_EXCEEDED:
+         case GNUNET_TUN_ICMPTYPE6_PACKET_TOO_BIG:
+         case GNUNET_TUN_ICMPTYPE6_PARAMETER_PROBLEM:
+           {
+             struct GNUNET_TUN_IPv6Header *ipp = (struct GNUNET_TUN_IPv6Header *) &icmp[1];
+             struct GNUNET_TUN_UdpHeader *udp = (struct GNUNET_TUN_UdpHeader *) &ipp[1];
+             
+             if (mlen != 0)
+               {
+                 /* sender did not strip ICMP payload? */
+                 GNUNET_break_op (0);
+                 return GNUNET_SYSERR;
+               }
+             size += sizeof (struct GNUNET_TUN_IPv6Header) + 8;
+             GNUNET_assert (8 == sizeof (struct GNUNET_TUN_UdpHeader));
+             make_up_icmpv6_payload (ts, ipp, udp);
+           }
+           break;
+         case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
+           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:
+         GNUNET_break_op (0);
+         return GNUNET_SYSERR;
+       }
+       msg->size = htons (size);
+       GNUNET_TUN_calculate_icmp_checksum (icmp,
+                                           &i2v[1], mlen);
+       (void) GNUNET_HELPER_send (helper_handle,
+                                  msg,
+                                  GNUNET_YES,
+                                  NULL, NULL);
+      }
+    }
+    break;
+  default:
+    GNUNET_assert (0);
+  }
+  GNUNET_CONTAINER_heap_update_cost (tunnel_heap, 
+                                    ts->heap_node,
+                                    GNUNET_TIME_absolute_get ().abs_value);
+  return GNUNET_OK;
 }
 
 
@@ -1413,7 +2082,7 @@ receive_udp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        sizeof (struct GNUNET_TUN_Layer2PacketHeader) +
        mlen;
       {
-       char buf[size];
+       char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun = (struct GNUNET_TUN_Layer2PacketHeader*) &msg[1];
        struct GNUNET_TUN_IPv4Header *ipv4 = (struct GNUNET_TUN_IPv4Header *) &tun[1];
@@ -1422,33 +2091,24 @@ receive_udp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV4);
-       ipv4->version = 4;
-       ipv4->header_length = sizeof (struct GNUNET_TUN_IPv4Header) / 4;
-       ipv4->diff_serv = 0;
-       ipv4->total_length = htons (sizeof (struct GNUNET_TUN_IPv4Header) +
-                                   sizeof (struct GNUNET_TUN_UdpHeader) +
-                                   mlen);
-       ipv4->identification = (uint16_t) GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
-                                                                   UINT16_MAX + 1);
-       ipv4->flags = 0;
-       ipv4->fragmentation_offset = 0;
-       ipv4->ttl = 255;
-       ipv4->protocol = IPPROTO_UDP;
-       ipv4->checksum = 0; 
-       ipv4->source_address = ts->destination_ip.v4;
-       ipv4->destination_address = ts->source_ip.v4;
-       ipv4->checksum =
-         GNUNET_CRYPTO_crc16_n (ipv4, sizeof (struct GNUNET_TUN_IPv4Header));
+       GNUNET_TUN_initialize_ipv4_header (ipv4,
+                                          IPPROTO_UDP,
+                                          sizeof (struct GNUNET_TUN_UdpHeader) + mlen,
+                                          &ts->destination_ip.v4,
+                                          &ts->source_ip.v4);
        if (0 == ntohs (reply->source_port))
-         udp->spt = htons (ts->destination_port);
+         udp->source_port = htons (ts->destination_port);
        else
-         udp->spt = reply->source_port;
+         udp->source_port = reply->source_port;
        if (0 == ntohs (reply->destination_port))
-         udp->dpt = htons (ts->source_port);
+         udp->destination_port = htons (ts->source_port);
        else
-         udp->dpt = reply->destination_port;
+         udp->destination_port = reply->destination_port;
        udp->len = htons (mlen + sizeof (struct GNUNET_TUN_UdpHeader));
-       udp->crc = 0; // FIXME: optional, but we might want to calculate this one anyway
+       GNUNET_TUN_calculate_udp4_checksum (ipv4,
+                                           udp,
+                                           &reply[1],
+                                           mlen);
        memcpy (&udp[1],
                &reply[1],
                mlen);
@@ -1467,7 +2127,7 @@ receive_udp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        sizeof (struct GNUNET_TUN_Layer2PacketHeader) +
        mlen;
       {
-       char buf[size];
+       char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun = (struct GNUNET_TUN_Layer2PacketHeader*) &msg[1];
        struct GNUNET_TUN_IPv6Header *ipv6 = (struct GNUNET_TUN_IPv6Header *) &tun[1];
@@ -1476,42 +2136,26 @@ receive_udp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV6);
-       ipv6->traffic_class_h = 0;
-       ipv6->version = 6;
-       ipv6->traffic_class_l = 0;
-       ipv6->flow_label = 0;
-       ipv6->payload_length = htons (sizeof (struct GNUNET_TUN_UdpHeader) + sizeof (struct GNUNET_TUN_IPv6Header) + mlen);
-       ipv6->next_header = IPPROTO_UDP;
-       ipv6->hop_limit = 255;
-       ipv6->source_address = ts->destination_ip.v6;
-       ipv6->destination_address = ts->source_ip.v6;
+       GNUNET_TUN_initialize_ipv6_header (ipv6,
+                                          IPPROTO_UDP,
+                                          sizeof (struct GNUNET_TUN_UdpHeader) + mlen,
+                                          &ts->destination_ip.v6,
+                                          &ts->source_ip.v6);
        if (0 == ntohs (reply->source_port))
-         udp->spt = htons (ts->destination_port);
+         udp->source_port = htons (ts->destination_port);
        else
-         udp->spt = reply->source_port;
+         udp->source_port = reply->source_port;
        if (0 == ntohs (reply->destination_port))
-         udp->dpt = htons (ts->source_port);
+         udp->destination_port = htons (ts->source_port);
        else
-         udp->dpt = reply->destination_port;
+         udp->destination_port = reply->destination_port;
        udp->len = htons (mlen + sizeof (struct GNUNET_TUN_UdpHeader));
-       udp->crc = 0;
+       GNUNET_TUN_calculate_udp6_checksum (ipv6,
+                                           udp,
+                                           &reply[1], mlen);
        memcpy (&udp[1],
                &reply[1],
                mlen);
-       {
-         uint32_t sum = 0;
-         sum =
-           GNUNET_CRYPTO_crc16_step (sum, &ipv6->source_address, 
-                                     sizeof (struct in6_addr) * 2);
-         uint32_t tmp = udp->len;
-         sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-         tmp = htons (IPPROTO_UDP);
-         sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-         sum = GNUNET_CRYPTO_crc16_step (sum, 
-                                         udp,
-                                         ntohs (udp->len));
-         udp->crc = GNUNET_CRYPTO_crc16_finish (sum);
-       }
        (void) GNUNET_HELPER_send (helper_handle,
                                   msg,
                                   GNUNET_YES,
@@ -1581,6 +2225,11 @@ receive_tcp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                inet_ntop (ts->af, &ts->source_ip, dbuf, sizeof (dbuf)),
                ts->source_port);
   }
+  if (data->tcp_header.off * 4 < sizeof (struct GNUNET_TUN_TcpHeader))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
   switch (ts->af)
   {
   case AF_INET:
@@ -1591,7 +2240,7 @@ receive_tcp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        sizeof (struct GNUNET_TUN_Layer2PacketHeader) +
        mlen;
       {
-       char buf[size];
+       char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun = (struct GNUNET_TUN_Layer2PacketHeader*) &msg[1];
        struct GNUNET_TUN_IPv4Header *ipv4 = (struct GNUNET_TUN_IPv4Header *) &tun[1];
@@ -1600,42 +2249,21 @@ receive_tcp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV4);
-       ipv4->version = 4;
-       ipv4->header_length = sizeof (struct GNUNET_TUN_IPv4Header) / 4;
-       ipv4->diff_serv = 0;
-       ipv4->total_length = htons (sizeof (struct GNUNET_TUN_IPv4Header) +
-                                   sizeof (struct GNUNET_TUN_TcpHeader) +
-                                   mlen);
-       ipv4->identification = (uint16_t) GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
-                                                                   UINT16_MAX + 1);
-       ipv4->flags = 0;
-       ipv4->fragmentation_offset = 0;
-       ipv4->ttl = 255;
-       ipv4->protocol = IPPROTO_TCP;
-       ipv4->checksum = 0; 
-       ipv4->source_address = ts->destination_ip.v4;
-       ipv4->destination_address = ts->source_ip.v4;
-       ipv4->checksum =
-         GNUNET_CRYPTO_crc16_n (ipv4, sizeof (struct GNUNET_TUN_IPv4Header));
+       GNUNET_TUN_initialize_ipv4_header (ipv4,
+                                          IPPROTO_TCP,
+                                          sizeof (struct GNUNET_TUN_TcpHeader) + mlen,
+                                          &ts->destination_ip.v4,
+                                          &ts->source_ip.v4);
        *tcp = data->tcp_header;
-       tcp->spt = htons (ts->destination_port);
-       tcp->dpt = htons (ts->source_port);
-       tcp->crc = 0;
+       tcp->source_port = htons (ts->destination_port);
+       tcp->destination_port = htons (ts->source_port);
+       GNUNET_TUN_calculate_tcp4_checksum (ipv4,
+                                           tcp,
+                                           &data[1],
+                                           mlen);
        memcpy (&tcp[1],
                &data[1],
                mlen);
-       {
-         uint32_t sum = 0;
-         uint32_t tmp;
-         
-         sum = GNUNET_CRYPTO_crc16_step (sum, 
-                                         &ipv4->source_address,
-                                         2 * sizeof (struct in_addr));   
-         tmp = htonl ((IPPROTO_TCP << 16) | (mlen + sizeof (struct GNUNET_TUN_TcpHeader)));
-         sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-         sum = GNUNET_CRYPTO_crc16_step (sum, tcp, mlen + sizeof (struct GNUNET_TUN_TcpHeader));
-         tcp->crc = GNUNET_CRYPTO_crc16_finish (sum);
-       }
        (void) GNUNET_HELPER_send (helper_handle,
                                   msg,
                                   GNUNET_YES,
@@ -1651,7 +2279,7 @@ receive_tcp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        sizeof (struct GNUNET_TUN_Layer2PacketHeader) +
        mlen;
       {
-       char buf[size];
+       char buf[size] GNUNET_ALIGN;
        struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) buf;
        struct GNUNET_TUN_Layer2PacketHeader *tun = (struct GNUNET_TUN_Layer2PacketHeader*) &msg[1];
        struct GNUNET_TUN_IPv6Header *ipv6 = (struct GNUNET_TUN_IPv6Header *) &tun[1];
@@ -1660,31 +2288,21 @@ receive_tcp_back (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
        msg->size = htons (size);
        tun->flags = htons (0);
        tun->proto = htons (ETH_P_IPV6);
-       ipv6->traffic_class_h = 0;
-       ipv6->version = 6;
-       ipv6->traffic_class_l = 0;
-       ipv6->flow_label = 0;
-       ipv6->payload_length = htons (sizeof (struct GNUNET_TUN_TcpHeader) + sizeof (struct GNUNET_TUN_IPv6Header) + mlen);
-       ipv6->next_header = IPPROTO_TCP;
-       ipv6->hop_limit = 255;
-       ipv6->source_address = ts->destination_ip.v6;
-       ipv6->destination_address = ts->source_ip.v6;
-       tcp->spt = htons (ts->destination_port);
-       tcp->dpt = htons (ts->source_port);
-       tcp->crc = 0;
-       {
-         uint32_t sum = 0;
-         uint32_t tmp;
-
-         sum = GNUNET_CRYPTO_crc16_step (sum, &ipv6->source_address, 2 * sizeof (struct in6_addr));
-         tmp = htonl (sizeof (struct GNUNET_TUN_TcpHeader) + mlen);
-         sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-         tmp = htonl (IPPROTO_TCP);
-         sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-         sum = GNUNET_CRYPTO_crc16_step (sum, tcp,
-                                         sizeof (struct GNUNET_TUN_TcpHeader) + mlen);
-         tcp->crc = GNUNET_CRYPTO_crc16_finish (sum);
-       }
+       GNUNET_TUN_initialize_ipv6_header (ipv6,
+                                          IPPROTO_TCP,
+                                          sizeof (struct GNUNET_TUN_TcpHeader) + mlen,
+                                          &ts->destination_ip.v6,
+                                          &ts->source_ip.v6);
+       *tcp = data->tcp_header;
+       tcp->source_port = htons (ts->destination_port);
+       tcp->destination_port = htons (ts->source_port);
+       GNUNET_TUN_calculate_tcp6_checksum (ipv6,
+                                           tcp,
+                                           &data[1],
+                                           mlen);
+       memcpy (&tcp[1],
+               &data[1],
+               mlen);
        (void) GNUNET_HELPER_send (helper_handle,
                                   msg,
                                   GNUNET_YES,
@@ -1716,7 +2334,7 @@ allocate_v4_address (struct in_addr *v4)
   struct in_addr addr;
   struct in_addr mask;
   struct in_addr rnd;
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
   unsigned int tries;
 
   GNUNET_assert (1 == inet_pton (AF_INET, ipv4addr, &addr));
@@ -1767,7 +2385,7 @@ allocate_v6_address (struct in6_addr *v6)
   struct in6_addr mask;
   struct in6_addr rnd;
   int i;
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
   unsigned int tries;
 
   GNUNET_assert (1 == inet_pton (AF_INET6, ipv6addr, &addr));
@@ -1775,7 +2393,7 @@ allocate_v6_address (struct in6_addr *v6)
   /* 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 */
@@ -1856,12 +2474,72 @@ expire_destination (struct DestinationEntry *except)
   struct DestinationEntry *de;
 
   de = GNUNET_CONTAINER_heap_peek (destination_heap);
+  GNUNET_assert (NULL != de);
   if (except == de)
     return; /* can't do this */
   free_destination_entry (de);
 }
 
 
+/**
+ * Allocate an IP address for the response.  
+ *
+ * @param result_af desired address family; set to the actual
+ *        address family; can initially be AF_UNSPEC if there
+ *        is no preference; will be set to AF_UNSPEC if the
+ *        allocation failed
+ * @param addr set to either v4 or v6 depending on which 
+ *         storage location was used; set to NULL if allocation failed
+ * @param v4 storage space for an IPv4 address
+ * @param v6 storage space for an IPv6 address
+ * @return GNUNET_OK normally, GNUNET_SYSERR if '*result_af' was
+ *         an unsupported address family (not AF_INET, AF_INET6 or AF_UNSPEC)
+ */
+static int
+allocate_response_ip (int *result_af,
+                     void **addr,
+                     struct in_addr *v4,
+                     struct in6_addr *v6)
+{
+  *addr = NULL;
+  switch (*result_af)
+  {
+  case AF_INET:
+    if (GNUNET_OK !=
+       allocate_v4_address (v4))
+      *result_af = AF_UNSPEC;
+    else
+      *addr = v4;
+    break;
+  case AF_INET6:
+    if (GNUNET_OK !=
+       allocate_v6_address (v6))
+      *result_af = AF_UNSPEC;
+    else
+      *addr = v6;
+    break;
+  case AF_UNSPEC:
+    if (GNUNET_OK ==
+       allocate_v4_address (v4))
+    {
+      *addr = v4;
+      *result_af = AF_INET;
+    }
+    else if (GNUNET_OK ==
+       allocate_v6_address (v6))
+    {
+      *addr = v6;
+      *result_af = AF_INET6;
+    }
+    break;
+  default:
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}                    
+
+
 /**
  * A client asks us to setup a redirection via some exit
  * node to a particular IP.  Setup the redirection and
@@ -1884,7 +2562,8 @@ service_redirect_to_ip (void *cls GNUNET_UNUSED, struct GNUNET_SERVER_Client *cl
   struct in6_addr v6;
   void *addr;
   struct DestinationEntry *de;
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
+  struct TunnelState *ts;
   
   /* validate and parse request */
   mlen = ntohs (message->size);
@@ -1922,40 +2601,11 @@ service_redirect_to_ip (void *cls GNUNET_UNUSED, struct GNUNET_SERVER_Client *cl
   }
 
   /* allocate response IP */
-  addr = NULL;
   result_af = (int) htonl (msg->result_af);
-  switch (result_af)
+  if (GNUNET_OK != allocate_response_ip (&result_af,
+                                        &addr,
+                                        &v4, &v6))
   {
-  case AF_INET:
-    if (GNUNET_OK !=
-       allocate_v4_address (&v4))
-      result_af = AF_UNSPEC;
-    else
-      addr = &v4;
-    break;
-  case AF_INET6:
-    if (GNUNET_OK !=
-       allocate_v6_address (&v6))
-      result_af = AF_UNSPEC;
-    else
-      addr = &v6;
-    break;
-  case AF_UNSPEC:
-    if (GNUNET_OK ==
-       allocate_v4_address (&v4))
-    {
-      addr = &v4;
-      result_af = AF_INET;
-    }
-    else if (GNUNET_OK ==
-       allocate_v6_address (&v6))
-    {
-      addr = &v6;
-      result_af = AF_INET6;
-    }
-    break;
-  default:
-    GNUNET_break (0);
     GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
     return;      
   }
@@ -2010,11 +2660,23 @@ service_redirect_to_ip (void *cls GNUNET_UNUSED, struct GNUNET_SERVER_Client *cl
                            1, GNUNET_NO);
   while (GNUNET_CONTAINER_multihashmap_size (destination_map) > max_destination_mappings)
     expire_destination (de);
-
+  
   /* setup tunnel to destination */
-  (void) create_tunnel_to_destination (de, 
-                                      (GNUNET_NO == ntohl (msg->nac)) ? NULL : client,
-                                      msg->request_id);
+  ts = create_tunnel_to_destination (de, 
+                                    (GNUNET_NO == ntohl (msg->nac)) ? NULL : client,
+                                    result_af,
+                                    msg->request_id);
+  switch (result_af)
+  {
+  case AF_INET:
+    ts->destination_ip.v4 = v4;
+    break;
+  case AF_INET6:
+    ts->destination_ip.v6 = v6;
+    break;
+  default:
+    GNUNET_assert (0);
+  }
   /* we're done */
   GNUNET_SERVER_receive_done (client, GNUNET_OK);
 }
@@ -2039,46 +2701,18 @@ service_redirect_to_service (void *cls GNUNET_UNUSED, struct GNUNET_SERVER_Clien
   struct in6_addr v6;
   void *addr;
   struct DestinationEntry *de;
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
+  struct TunnelState *ts;
   
   /*  parse request */
   msg = (const struct RedirectToServiceRequestMessage *) message;
 
   /* allocate response IP */
-  addr = NULL;
   result_af = (int) htonl (msg->result_af);
-  switch (result_af)
+  if (GNUNET_OK != allocate_response_ip (&result_af,
+                                        &addr,
+                                        &v4, &v6))
   {
-  case AF_INET:
-    if (GNUNET_OK !=
-       allocate_v4_address (&v4))
-      result_af = AF_UNSPEC;
-    else
-      addr = &v4;
-    break;
-  case AF_INET6:
-    if (GNUNET_OK !=
-       allocate_v6_address (&v6))
-      result_af = AF_UNSPEC;
-    else
-      addr = &v6;
-    break;
-  case AF_UNSPEC:
-    if (GNUNET_OK ==
-       allocate_v4_address (&v4))
-    {
-      addr = &v4;
-      result_af = AF_INET;
-    }
-    else if (GNUNET_OK ==
-       allocate_v6_address (&v6))
-    {
-      addr = &v6;
-      result_af = AF_INET6;
-    }
-    break;
-  default:
-    GNUNET_break (0);
     GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
     return;      
   }
@@ -2129,9 +2763,21 @@ service_redirect_to_service (void *cls GNUNET_UNUSED, struct GNUNET_SERVER_Clien
                                                GNUNET_TIME_absolute_ntoh (msg->expiration_time).abs_value);
   while (GNUNET_CONTAINER_multihashmap_size (destination_map) > max_destination_mappings)
     expire_destination (de);
-  (void) create_tunnel_to_destination (de,
-                                      (GNUNET_NO == ntohl (msg->nac)) ? NULL : client,
-                                      msg->request_id);
+  ts = create_tunnel_to_destination (de,
+                                    (GNUNET_NO == ntohl (msg->nac)) ? NULL : client,
+                                    result_af,
+                                    msg->request_id);
+  switch (result_af)
+  {
+  case AF_INET:
+    ts->destination_ip.v4 = v4;
+    break;
+  case AF_INET6:
+    ts->destination_ip.v6 = v6;
+    break;
+  default:
+    GNUNET_assert (0);
+  }
   /* we're done */
   GNUNET_SERVER_receive_done (client, GNUNET_OK);
 }
@@ -2172,16 +2818,8 @@ inbound_tunnel_cb (void *cls, struct GNUNET_MESH_Tunnel *tunnel,
 static void
 tunnel_cleaner (void *cls, const struct GNUNET_MESH_Tunnel *tunnel, void *tunnel_ctx)
 {
-  struct TunnelState *ts = tunnel_ctx;
-
-  if (NULL == ts)
-  {
-    GNUNET_break (0);
-    return;     
-  }
-  GNUNET_assert (ts->tunnel == tunnel);
-  ts->tunnel = NULL;
-  free_tunnel_state (ts);
+  /* we don't have inbound tunnels, so this function should never be called */
+  GNUNET_break (0);
 }
 
 
@@ -2195,7 +2833,7 @@ tunnel_cleaner (void *cls, const struct GNUNET_MESH_Tunnel *tunnel, void *tunnel
  */
 static int
 cleanup_destination (void *cls,
-                    const GNUNET_HashCode *key,
+                    const struct GNUNET_HashCode *key,
                     void *value)
 {
   struct DestinationEntry *de = value;
@@ -2215,7 +2853,7 @@ cleanup_destination (void *cls,
  */
 static int
 cleanup_tunnel (void *cls,
-               const GNUNET_HashCode *key,
+               const struct GNUNET_HashCode *key,
                void *value)
 {
   struct TunnelState *ts = value;
@@ -2282,7 +2920,7 @@ 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++)
@@ -2300,7 +2938,7 @@ cleanup (void *cls GNUNET_UNUSED,
  */
 static int
 cleanup_tunnel_client (void *cls,
-                      const GNUNET_HashCode *key,
+                      const struct GNUNET_HashCode *key,
                       void *value)
 {
   struct GNUNET_SERVER_Client *client = cls;
@@ -2325,7 +2963,7 @@ cleanup_tunnel_client (void *cls,
  */
 static int
 cleanup_destination_client (void *cls,
-                           const GNUNET_HashCode *key,
+                           const struct GNUNET_HashCode *key,
                            void *value)
 {
   struct GNUNET_SERVER_Client *client = cls;
@@ -2378,17 +3016,16 @@ run (void *cls,
 {
   static const struct GNUNET_SERVER_MessageHandler service_handlers[] = {
     /* callback, cls, type, size */
-    {&service_redirect_to_ip, NULL, GNUNET_MESSAGE_TYPE_VPN_CLIENT_REDIRECT_TO_IP, 0},
-    {&service_redirect_to_service, NULL, 
+    { &service_redirect_to_ip, NULL, GNUNET_MESSAGE_TYPE_VPN_CLIENT_REDIRECT_TO_IP, 0},
+    { &service_redirect_to_service, NULL, 
      GNUNET_MESSAGE_TYPE_VPN_CLIENT_REDIRECT_TO_SERVICE, 
      sizeof (struct RedirectToServiceRequestMessage) },
     {NULL, NULL, 0, 0}
   };
   static const struct GNUNET_MESH_MessageHandler mesh_handlers[] = {
-    {receive_udp_back, GNUNET_MESSAGE_TYPE_VPN_SERVICE_UDP_BACK, 0},
-    {receive_tcp_back, GNUNET_MESSAGE_TYPE_VPN_SERVICE_TCP_BACK, 0},
-    {receive_udp_back, GNUNET_MESSAGE_TYPE_VPN_REMOTE_UDP_BACK, 0},
-    {receive_tcp_back, GNUNET_MESSAGE_TYPE_VPN_REMOTE_TCP_BACK, 0},
+    { &receive_udp_back, GNUNET_MESSAGE_TYPE_VPN_UDP_REPLY, 0},
+    { &receive_tcp_back, GNUNET_MESSAGE_TYPE_VPN_TCP_DATA_TO_VPN, 0},
+    { &receive_icmp_back, GNUNET_MESSAGE_TYPE_VPN_ICMP_TO_VPN, 0},
     {NULL, 0, 0}
   };
   static const GNUNET_MESH_ApplicationType types[] = {
@@ -2402,6 +3039,15 @@ run (void *cls,
   struct in_addr v4;
   struct in6_addr v6;
 
+  if (GNUNET_YES !=
+      GNUNET_OS_check_helper_binary ("gnunet-helper-vpn"))
+  {
+    fprintf (stderr,
+            "`%s' is not SUID, refusing to run.\n",
+            "gnunet-helper-vpn");
+    global_ret = 1;
+    return;
+  }
   cfg = cfg_;
   stats = GNUNET_STATISTICS_create ("vpn", cfg);
   if (GNUNET_OK !=
@@ -2413,9 +3059,9 @@ run (void *cls,
                                             &max_tunnel_mappings))
     max_tunnel_mappings = 200;
 
-  destination_map = GNUNET_CONTAINER_multihashmap_create (max_destination_mappings * 2);
+  destination_map = GNUNET_CONTAINER_multihashmap_create (max_destination_mappings * 2, GNUNET_NO);
   destination_heap = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
-  tunnel_map = GNUNET_CONTAINER_multihashmap_create (max_tunnel_mappings * 2);
+  tunnel_map = GNUNET_CONTAINER_multihashmap_create (max_tunnel_mappings * 2, GNUNET_NO);
   tunnel_heap = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
 
 
@@ -2429,69 +3075,89 @@ run (void *cls,
     return;
   }
   vpn_argv[1] = ifname;
-  if ( (GNUNET_SYSERR ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV6ADDR",
-                                              &ipv6addr) ||
-       (1 != inet_pton (AF_INET6, ipv6addr, &v6))) )
-  {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No valid entry 'IPV6ADDR' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
-  }
-  vpn_argv[2] = ipv6addr;
-  if (GNUNET_SYSERR ==
-      GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV6PREFIX",
-                                             &ipv6prefix_s))
+  if (GNUNET_OK == GNUNET_NETWORK_test_pf (PF_INET6))
   {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No entry 'IPV6PREFIX' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+    if ( (GNUNET_SYSERR ==
+         GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV6ADDR",
+                                                &ipv6addr) ||
+         (1 != inet_pton (AF_INET6, ipv6addr, &v6))) )
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No valid entry 'IPV6ADDR' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    vpn_argv[2] = ipv6addr;
+    if (GNUNET_SYSERR ==
+       GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV6PREFIX",
+                                              &ipv6prefix_s))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No entry 'IPV6PREFIX' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    vpn_argv[3] = ipv6prefix_s;
+    if ( (GNUNET_OK !=
+         GNUNET_CONFIGURATION_get_value_number (cfg, "vpn",
+                                                "IPV6PREFIX",
+                                                &ipv6prefix)) ||
+        (ipv6prefix >= 127) )
+    {
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
   }
-  vpn_argv[3] = ipv6prefix_s;
-  if ( (GNUNET_OK !=
-       GNUNET_CONFIGURATION_get_value_number (cfg, "vpn",
-                                              "IPV6PREFIX",
-                                              &ipv6prefix)) ||
-       (ipv6prefix >= 127) )
+  else
   {
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+               _("IPv6 support disabled as this system does not support IPv6\n"));
+    vpn_argv[2] = GNUNET_strdup ("-");
+    vpn_argv[3] = GNUNET_strdup ("-");
   }
-
-  if ( (GNUNET_SYSERR ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV4ADDR",
-                                              &ipv4addr) ||
-       (1 != inet_pton (AF_INET, ipv4addr, &v4))) )
+  if (GNUNET_OK == GNUNET_NETWORK_test_pf (PF_INET))
   {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No valid entry for 'IPV4ADDR' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+    if ( (GNUNET_SYSERR ==
+         GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV4ADDR",
+                                                &ipv4addr) ||
+         (1 != inet_pton (AF_INET, ipv4addr, &v4))) )
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No valid entry for 'IPV4ADDR' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    vpn_argv[4] = ipv4addr;
+    if ( (GNUNET_SYSERR ==
+         GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV4MASK",
+                                                &ipv4mask) ||
+         (1 != inet_pton (AF_INET, ipv4mask, &v4))) )
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No valid entry 'IPV4MASK' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    vpn_argv[5] = ipv4mask;
   }
-  vpn_argv[4] = ipv4addr;
-  if ( (GNUNET_SYSERR ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, "vpn", "IPV4MASK",
-                                              &ipv4mask) ||
-       (1 != inet_pton (AF_INET, ipv4mask, &v4))) )
+  else
   {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No valid entry 'IPV4MASK' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+               _("IPv4 support disabled as this system does not support IPv4\n"));
+    vpn_argv[4] = GNUNET_strdup ("-");
+    vpn_argv[5] = GNUNET_strdup ("-");
   }
-  vpn_argv[5] = ipv4mask;
   vpn_argv[6] = NULL;
 
   mesh_handle =
-    GNUNET_MESH_connect (cfg_, 42 /* queue length */, NULL, 
+    GNUNET_MESH_connect (cfg_, NULL, 
                         &inbound_tunnel_cb, 
                         &tunnel_cleaner, 
                         mesh_handlers,
                         types);
-  helper_handle = GNUNET_HELPER_start ("gnunet-helper-vpn", vpn_argv,
-                                      &message_token, NULL);
+  helper_handle = GNUNET_HELPER_start (GNUNET_NO,
+                                      "gnunet-helper-vpn", vpn_argv,
+                                      &message_token, NULL, NULL);
   nc = GNUNET_SERVER_notification_context_create (server, 1);
   GNUNET_SERVER_add_handlers (server, service_handlers);
   GNUNET_SERVER_disconnect_notify (server, &client_disconnect, NULL);
@@ -2512,7 +3178,7 @@ main (int argc, char *const *argv)
   return (GNUNET_OK ==
           GNUNET_SERVICE_run (argc, argv, "vpn", 
                              GNUNET_SERVICE_OPTION_NONE,
-                              &run, NULL)) ? 0 : 1;
+                              &run, NULL)) ? global_ret : 1;
 }
 
 /* end of gnunet-service-vpn.c */