-actually enable free regex specification, in binary for now
[oweals/gnunet.git] / src / exit / gnunet-daemon-exit.c
index 7097d71a0ce90c152506b0230bb999d02f1448e9..aab25072abed3175b43b5fc8083644f3746548cc 100644 (file)
  * @author Christian Grothoff
  *
  * TODO:
- * - setup_fresh_address is not implemented
- * - various functions are not documented
- * - update_state_map is dead, do we need something like it still?
- * - need proper message headers for mesh P2P messages
- */
-#include <platform.h>
-#include <gnunet_common.h>
-#include <gnunet_program_lib.h>
-#include <gnunet_protocols.h>
-#include <gnunet_applications.h>
-#include <gnunet_mesh_service.h>
-#include <gnunet_constants.h>
-#include <string.h>
-
-
-/* see http://www.iana.org/assignments/ethernet-numbers */
-#ifndef ETH_P_IPV4
-#define ETH_P_IPV4 0x0800
-#endif
-
-#ifndef ETH_P_IPV6
-#define ETH_P_IPV6 0x86DD
-#endif
-
-
-GNUNET_NETWORK_STRUCT_BEGIN
-/**
- * Header from Linux TUN interface.
- */ 
-struct tun_header
-{
-  /**
-   * Some flags (unused).
-   */ 
-  uint16_t flags;
-
-  /**
-   * Here we get an ETH_P_-number.
-   */
-  uint16_t proto;
-};
-
-/**
- * Standard IPv4 header.
+ * - test
+ *
+ * Design:
+ * - which code should advertise services? the service model is right
+ *   now a bit odd, especially as this code DOES the exit and knows
+ *   the DNS "name", but OTOH this is clearly NOT the place to advertise
+ *   the service's existence; maybe the daemon should turn into a 
+ *   service with an API to add local-exit services dynamically?
  */
-struct ip4_header
-{
-  unsigned header_length:4 GNUNET_PACKED;
-  unsigned version:4 GNUNET_PACKED;
-  uint8_t diff_serv;
-  uint16_t total_length GNUNET_PACKED;
-  uint16_t identification GNUNET_PACKED;
-  unsigned flags:3 GNUNET_PACKED;
-  unsigned fragmentation_offset:13 GNUNET_PACKED;
-  uint8_t ttl;
-  uint8_t protocol;
-  uint16_t checksum GNUNET_PACKED;
-  struct in_addr source_address GNUNET_PACKED;
-  struct in_addr destination_address GNUNET_PACKED;
-};
+#include "platform.h"
+#include "gnunet_util_lib.h"
+#include "gnunet_protocols.h"
+#include "gnunet_applications.h"
+#include "gnunet_mesh_service.h"
+#include "gnunet_statistics_service.h"
+#include "gnunet_constants.h"
+#include "gnunet_tun_lib.h"
+#include "gnunet_regex_lib.h"
+#include "exit.h"
 
 /**
- * Standard IPv6 header.
+ * Maximum path compression length for mesh regex announcing for IPv4 address
+ * based regex.
  */
-struct ip6_header
-{
-  unsigned traffic_class_h:4 GNUNET_PACKED;
-  unsigned version:4 GNUNET_PACKED;
-  unsigned traffic_class_l:4 GNUNET_PACKED;
-  unsigned flow_label:20 GNUNET_PACKED;
-  uint16_t payload_length GNUNET_PACKED;
-  uint8_t next_header;
-  uint8_t hop_limit;
-  struct in6_addr source_address GNUNET_PACKED;
-  struct in6_addr destination_address GNUNET_PACKED;
-};
-
-#define TCP_FLAG_SYN 2
-
-struct tcp_packet
-{
-  unsigned spt:16 GNUNET_PACKED;
-  unsigned dpt:16 GNUNET_PACKED;
-  unsigned seq:32 GNUNET_PACKED;
-  unsigned ack:32 GNUNET_PACKED;
-  unsigned off:4 GNUNET_PACKED;
-  unsigned rsv:4 GNUNET_PACKED;
-  unsigned flg:8 GNUNET_PACKED;
-  unsigned wsz:16 GNUNET_PACKED;
-  unsigned crc:16 GNUNET_PACKED;
-  unsigned urg:16 GNUNET_PACKED;
-};
+#define REGEX_MAX_PATH_LEN_IPV4 4
 
 /**
- * UDP packet header.
+ * Maximum path compression length for mesh regex announcing for IPv6 address
+ * based regex.
  */
-struct udp_packet
-{
-  uint16_t spt GNUNET_PACKED;
-  uint16_t dpt GNUNET_PACKED;
-  uint16_t len GNUNET_PACKED;
-  uint16_t crc GNUNET_PACKED;
-};
+#define REGEX_MAX_PATH_LEN_IPV6 8
 
-/**
- * DNS header.
- */
-struct dns_header
-{
-  uint16_t id GNUNET_PACKED;
-  uint16_t flags GNUNET_PACKED;
-  uint16_t qdcount GNUNET_PACKED;
-  uint16_t ancount GNUNET_PACKED;
-  uint16_t nscount GNUNET_PACKED;
-  uint16_t arcount GNUNET_PACKED;
-};
-GNUNET_NETWORK_STRUCT_END
 
 /**
  * Information about an address.
@@ -288,7 +203,7 @@ struct TunnelState
   /**
    * Key this state has in the connections_map.
    */
-  GNUNET_HashCode state_key;
+  struct GNUNET_HashCode state_key;
 
   /**
    * Associated service record, or NULL for no service.
@@ -318,6 +233,11 @@ struct TunnelState
 };
 
 
+/**
+ * Return value from 'main'.
+ */
+static int global_ret;
+
 /**
  * The handle to the configuration used throughout the process
  */
@@ -331,13 +251,34 @@ 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.
+ */
+static struct GNUNET_STATISTICS_Handle *stats;
+
 /**
  * The handle to mesh
  */
@@ -357,7 +298,7 @@ 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 = 200;
+static unsigned long long max_connections;
 
 /**
  * This hashmaps saves interesting things about the configured UDP services
@@ -369,6 +310,26 @@ static struct GNUNET_CONTAINER_MultiHashMap *udp_services;
  */
 static struct GNUNET_CONTAINER_MultiHashMap *tcp_services;
 
+/**
+ * Are we an IPv4-exit?
+ */
+static int ipv4_exit;
+
+/**
+ * Are we an IPv6-exit?
+ */
+static int ipv6_exit;
+
+/**
+ * Do we support IPv4 at all on the TUN interface?
+ */
+static int ipv4_enabled;
+
+/**
+ * Do we support IPv6 at all on the TUN interface?
+ */
+static int ipv6_enabled;
+
 
 /**
  * Given IP information about a connection, calculate the respective
@@ -378,12 +339,12 @@ static struct GNUNET_CONTAINER_MultiHashMap *tcp_services;
  * @param ri information about the connection
  */
 static void
-hash_redirect_info (GNUNET_HashCode *hash, 
+hash_redirect_info (struct GNUNET_HashCode *hash, 
                    const struct RedirectInformation *ri)
 {
   char *off;
 
-  memset (hash, 0, sizeof (GNUNET_HashCode));
+  memset (hash, 0, sizeof (struct GNUNET_HashCode));
   /* the GNUnet hashmap only uses the first sizeof(unsigned int) of the hash,
      so we put the IP address in there (and hope for few collisions) */
   off = (char*) hash;
@@ -442,12 +403,19 @@ get_redirect_state (int af,
                    uint16_t destination_port,
                    const void *local_ip,
                    uint16_t local_port,
-                   GNUNET_HashCode *state_key)
+                   struct GNUNET_HashCode *state_key)
 {
   struct RedirectInformation ri;
-  GNUNET_HashCode key;
+  struct 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);
@@ -483,20 +451,20 @@ 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)
+             const struct GNUNET_HashCode *desc,
+             uint16_t destination_port)
 {
-  char key[sizeof (GNUNET_HashCode) + sizeof (uint16_t)];
+  char key[sizeof (struct GNUNET_HashCode) + sizeof (uint16_t)];
 
-  memcpy (&key[0], &dpt, sizeof (uint16_t));
-  memcpy (&key[sizeof(uint16_t)], desc, sizeof (GNUNET_HashCode));
+  memcpy (&key[0], &destination_port, sizeof (uint16_t));
+  memcpy (&key[sizeof(uint16_t)], desc, sizeof (struct GNUNET_HashCode));
   return GNUNET_CONTAINER_multihashmap_get (service_map,
-                                           (GNUNET_HashCode *) key);
+                                           (struct GNUNET_HashCode *) key);
 }
 
 
@@ -510,7 +478,7 @@ find_service (struct GNUNET_CONTAINER_MultiHashMap *service_map,
  */
 static int
 free_service_record (void *cls,
-                    const GNUNET_HashCode *key,
+                    const struct GNUNET_HashCode *key,
                     void *value)
 {
   struct LocalService *service = value;
@@ -527,33 +495,33 @@ 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)];
-  GNUNET_HashCode desc;
+  char key[sizeof (struct GNUNET_HashCode) + sizeof (uint16_t)];
+  struct GNUNET_HashCode desc;
 
   GNUNET_CRYPTO_hash (name, strlen (name) + 1, &desc);
   service->name = GNUNET_strdup (name);
-  memcpy (&key[0], &dpt, sizeof (uint16_t));
-  memcpy (&key[sizeof(uint16_t)], &desc, sizeof (GNUNET_HashCode));
+  memcpy (&key[0], &destination_port, sizeof (uint16_t));
+  memcpy (&key[sizeof(uint16_t)], &desc, sizeof (struct GNUNET_HashCode));
   if (GNUNET_OK !=
       GNUNET_CONTAINER_multihashmap_put (service_map,
-                                        (GNUNET_HashCode *) key,
+                                        (struct GNUNET_HashCode *) key,
                                         service,
                                         GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
   {
-    free_service_record (NULL, (GNUNET_HashCode *) key, service);
+    free_service_record (NULL, (struct GNUNET_HashCode *) key, service);
     GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                _("Got duplicate service records for `%s:%u'\n"),
                name,
-               (unsigned int) dpt);
+               (unsigned int) destination_port);
   }
 }
 
@@ -575,6 +543,19 @@ 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 */, 
+                                              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;
@@ -585,12 +566,14 @@ send_to_peer_notify_callback (void *cls, size_t size, void *buf)
   if (NULL != (tnq = s->head))
     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);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes transmitted via mesh tunnels"),
+                           size, GNUNET_NO);
   return size;
 }
 
@@ -599,55 +582,213 @@ 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 */,
+                                              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)
   {
-    dp = (GNUNET_HashCode *) &msg[1];
-    *dp = *desc;  
-    memcpy (&dp[1], payload, payload_length);
+  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);
   }
-  else
+  switch (protocol)
+  {
+  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;
+  }
+  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);
 }
 
 
@@ -663,15 +804,32 @@ send_packet_to_mesh_tunnel (struct GNUNET_MESH_Tunnel *mesh_tunnel,
  *                       be the original destination address)
  */
 static void
-udp_from_helper (const struct udp_packet *udp, 
+udp_from_helper (const struct GNUNET_TUN_UdpHeader *udp, 
                 size_t pktlen,
                 int af,
                 const void *destination_ip, 
                 const void *source_ip)
 {
   struct TunnelState *state;
+  struct TunnelMessageQueue *tnq;
+  struct GNUNET_EXIT_UdpReplyMessage *urm;
+  size_t mlen;
 
-  if (pktlen < sizeof (struct udp_packet))
+  {
+    char sbuf[INET6_ADDRSTRLEN];
+    char dbuf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Received UDP packet going from %s:%u to %s:%u\n",
+               inet_ntop (af,
+                          source_ip,
+                          sbuf, sizeof (sbuf)),
+               (unsigned int) ntohs (udp->source_port),
+               inet_ntop (af,
+                          destination_ip,
+                          dbuf, sizeof (dbuf)),
+               (unsigned int) ntohs (udp->destination_port));
+  }
+  if (pktlen < sizeof (struct GNUNET_TUN_UdpHeader))
   {
     /* blame kernel */
     GNUNET_break (0);
@@ -685,22 +843,30 @@ udp_from_helper (const struct udp_packet *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 udp_packet),
-                             NULL,
-                             state->serv != NULL
-                             ? GNUNET_MESSAGE_TYPE_VPN_SERVICE_UDP_BACK 
-                             : GNUNET_MESSAGE_TYPE_VPN_REMOTE_UDP_BACK);
+                             tnq);
 }
 
 
@@ -708,7 +874,7 @@ udp_from_helper (const struct udp_packet *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)
@@ -716,17 +882,35 @@ udp_from_helper (const struct udp_packet *udp,
  *                       be the original destination address)
  */
 static void
-tcp_from_helper (const struct tcp_packet *tcp, 
+tcp_from_helper (const struct GNUNET_TUN_TcpHeader *tcp, 
                 size_t pktlen,
                 int af,
                 const void *destination_ip,
                 const void *source_ip)
 {
   struct TunnelState *state;
-  char buf[pktlen];
-  struct tcp_packet *mtcp;
+  char buf[pktlen] GNUNET_ALIGN;
+  struct GNUNET_TUN_TcpHeader *mtcp;
+  struct GNUNET_EXIT_TcpDataMessage *tdm;
+  struct TunnelMessageQueue *tnq;
+  size_t mlen;
 
-  if (pktlen < sizeof (struct tcp_packet))
+  {
+    char sbuf[INET6_ADDRSTRLEN];
+    char dbuf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "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->source_port),
+               inet_ntop (af,
+                          destination_ip,
+                          dbuf, sizeof (dbuf)),
+               (unsigned int) ntohs (tcp->destination_port));
+  }
+  if (pktlen < sizeof (struct GNUNET_TUN_TcpHeader))
   {
     /* blame kernel */
     GNUNET_break (0);
@@ -734,30 +918,44 @@ tcp_from_helper (const struct tcp_packet *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;
   }
   /* mug port numbers and crc to avoid information leakage;
      sender will need to lookup the correct values anyway */
   memcpy (buf, tcp, pktlen);  
-  mtcp = (struct tcp_packet *) buf;
-  mtcp->spt = 0;
-  mtcp->dpt = 0;
+  mtcp = (struct GNUNET_TUN_TcpHeader *) buf;
+  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,
-                             state->serv != NULL
-                             ? GNUNET_MESSAGE_TYPE_VPN_SERVICE_TCP_BACK 
-                             : GNUNET_MESSAGE_TYPE_VPN_REMOTE_TCP_BACK);
+                             tnq);
 }
 
 
@@ -768,108 +966,134 @@ tcp_from_helper (const struct tcp_packet *tcp,
  * @param client unsued
  * @param message message received from helper
  */
-static void
+static int
 message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
                const struct GNUNET_MessageHeader *message)
 {
-  const struct tun_header *pkt_tun;
+  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);
   if (ntohs (message->type) != GNUNET_MESSAGE_TYPE_VPN_HELPER)
   {
     GNUNET_break (0);
-    return;
+    return GNUNET_OK;
   }
   size = ntohs (message->size);
-  if (size < sizeof (struct tun_header) + sizeof (struct GNUNET_MessageHeader))
+  if (size < sizeof (struct GNUNET_TUN_Layer2PacketHeader) + sizeof (struct GNUNET_MessageHeader))
   {
     GNUNET_break (0);
-    return;
+    return GNUNET_OK;
   }
-  pkt_tun = (const struct tun_header *) &message[1];
-  size -= sizeof (struct tun_header) + sizeof (struct GNUNET_MessageHeader);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from TUN"),
+                           size, GNUNET_NO);
+  pkt_tun = (const struct GNUNET_TUN_Layer2PacketHeader *) &message[1];
+  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 ip6_header *pkt6;
+      const struct GNUNET_TUN_IPv4Header *pkt4;
 
-      if (size < sizeof (struct ip6_header))
+      if (size < sizeof (struct GNUNET_TUN_IPv4Header))
       {
        /* Kernel to blame? */
        GNUNET_break (0);
-       return;
+        return GNUNET_OK;
       }
-      pkt6 = (struct ip6_header *) &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;
+        return GNUNET_OK;
       }
-      size -= sizeof (struct ip6_header);
-      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 GNUNET_OK;
+      }
+      
+      size -= sizeof (struct GNUNET_TUN_IPv4Header);
+      switch (pkt4->protocol)
       {
       case IPPROTO_UDP:
-       udp_from_helper ((const struct udp_packet *) &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 tcp_packet *) &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"));
-       return;
+                   _("IPv4 packet with unsupported next header %u received.  Ignored.\n"),
+                   (int) pkt4->protocol);
+        return GNUNET_OK;
       }
     }
     break;
-  case ETH_P_IPV4:
+  case ETH_P_IPV6:
     {
-      const struct ip4_header *pkt4;
+      const struct GNUNET_TUN_IPv6Header *pkt6;
 
-      if (size < sizeof (struct ip4_header))
+      if (size < sizeof (struct GNUNET_TUN_IPv6Header))
       {
        /* Kernel to blame? */
        GNUNET_break (0);
-       return;
+        return GNUNET_OK;
       }
-      pkt4 = (const struct ip4_header *) &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;
+        return GNUNET_OK;
       }
-      if (pkt4->header_length * 4 != sizeof (struct ip4_header))
-      {
-       GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                   _("IPv4 packet options received.  Ignored.\n"));
-       return;
-      }
-      size -= sizeof (struct ip4_header);
-      switch (pkt4->protocol)
+      size -= sizeof (struct GNUNET_TUN_IPv6Header);
+      switch (pkt6->next_header)
       {
       case IPPROTO_UDP:
-       udp_from_helper ((const struct udp_packet *) &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 tcp_packet *) &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"));
-       return;
+                   _("IPv6 packet with unsupported next header %d received.  Ignored.\n"),
+                    pkt6->next_header);
+        return GNUNET_OK;
       }
     }
     break;
@@ -879,6 +1103,7 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
                ntohs (pkt_tun->proto));
     break;
   }
+  return GNUNET_OK;
 }
 
 
@@ -892,42 +1117,88 @@ message_token (void *cls GNUNET_UNUSED, void *client GNUNET_UNUSED,
  */
 static void
 setup_fresh_address (int af,
-                    int proto,
+                    uint8_t proto,
                     struct SocketAddress *local_address)
 {
+  local_address->af = af;
+  local_address->proto = (uint8_t) proto;
+  /* default "local" port range is often 32768--61000,
+     so we pick a random value in that range */         
+  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];
-      uint32_t tmp;
-      uint32_t tmp2;
-      
-      GNUNET_assert (1 == inet_pton (AF_INET, ipv4addr, &tmp));
-      GNUNET_assert (1 == inet_pton (AF_INET, ipv4mask, &tmp2));
-      // FIXME
-      /* This should be a noop */
-      tmp = tmp & tmp2;
-      tmp |= ntohl (*((uint32_t *) /*tunnel*/ 42)) & (~tmp2);
-      
-      // pkt4->source_address.s_addr = tmp;
+      struct in_addr addr;
+      struct in_addr mask;
+      struct in_addr rnd;
+
+      addr = exit_ipv4addr;
+      mask = exit_ipv4mask;
+      if (0 == ~mask.s_addr)
+      {
+       /* only one valid IP anyway */
+       local_address->address.ipv4 = addr;
+       return;
+      }
+      /* Given 192.168.0.1/255.255.0.0, we want a mask 
+        of '192.168.255.255', thus:  */
+      mask.s_addr = addr.s_addr | ~mask.s_addr;
+      /* Pick random IPv4 address within the subnet, except 'addr' or 'mask' itself */
+      do
+       {
+         rnd.s_addr = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
+                                                UINT32_MAX);   
+         local_address->address.ipv4.s_addr = (addr.s_addr | rnd.s_addr) & mask.s_addr;
+       }
+      while ( (local_address->address.ipv4.s_addr == addr.s_addr) ||
+             (local_address->address.ipv4.s_addr == mask.s_addr) );
     }
     break;
   case AF_INET6:
     {
-      const char *ipv6addr = exit_argv[2];
-      /* Generate a new src-address
-       * This takes as much from the address of the tunnel as fits into
-       * the host-mask*/
-      unsigned long long ipv6prefix_r = (ipv6prefix + 7) / 8;
-      inet_pton (AF_INET6, ipv6addr, &local_address->address.ipv6);
-      if (ipv6prefix_r < (16 - sizeof (void *)))
-       ipv6prefix_r = 16 - sizeof (void *);
+      struct in6_addr addr;
+      struct in6_addr mask;
+      struct in6_addr rnd;
+      int i;
+      
+      addr = exit_ipv6addr;
+      GNUNET_assert (ipv6prefix < 128);
+      if (ipv6prefix == 127)
+      {
+       /* only one valid IP anyway */
+       local_address->address.ipv6 = addr;
+       return;
+      }
+      /* Given ABCD::/96, we want a mask of 'ABCD::FFFF:FFFF,
+        thus: */
+      mask = addr;
+      for (i=127;i>=ipv6prefix;i--)
+       mask.s6_addr[i / 8] |= (1 << (i % 8));
       
-      unsigned int offset = ipv6prefix_r - (16 - sizeof (void *));
-      // memcpy ((((char *) &pkt6->source_address)) + ipv6prefix_r, ((char *) &tunnel) + offset, 16 - ipv6prefix_r);
-      offset++;
+      /* Pick random IPv6 address within the subnet, except 'addr' or 'mask' itself */
+      do
+       {
+         for (i=0;i<16;i++)
+         {
+           rnd.s6_addr[i] = (unsigned char) GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
+                                                                      256);
+           local_address->address.ipv6.s6_addr[i]
+             = (addr.s6_addr[i] | rnd.s6_addr[i]) & mask.s6_addr[i];
+         }
+       }
+      while ( (0 == memcmp (&local_address->address.ipv6,
+                           &addr,
+                           sizeof (struct in6_addr))) ||
+             (0 == memcmp (&local_address->address.ipv6,
+                           &mask,
+                           sizeof (struct in6_addr))) );
     }
     break;
   default:
@@ -937,27 +1208,60 @@ setup_fresh_address (int af,
 
 
 /**
- * FIXME: document!
+ * We are starting a fresh connection (TCP or UDP) and need
+ * to pick a source port and IP address (within the correct
+ * range and address family) to associate replies with the
+ * connection / correct mesh tunnel.  This function generates
+ * a "fresh" source IP and source port number for a connection
+ * After picking a good source address, this function sets up
+ * the state in the 'connections_map' and 'connections_heap'
+ * to allow finding the state when needed later.  The function
+ * also makes sure that we remain within memory limits by
+ * cleaning up 'old' states.
+ *
+ * @param state skeleton state to setup a record for; should
+ *              'state->ri.remote_address' filled in so that
+ *              this code can determine which AF/protocol is
+ *              going to be used (the 'tunnel' should also
+ *              already be set); after calling this function,
+ *              heap_node and the local_address will be
+ *              also initialized (heap_node != NULL can be
+ *              used to test if a state has been fully setup).
  */
 static void
 setup_state_record (struct TunnelState *state)
 {
-  GNUNET_HashCode key;
+  struct GNUNET_HashCode key;
   struct TunnelState *s;
 
   /* generate fresh, unique address */
   do
   {
-    setup_fresh_address (state->serv->address.af,
-                        state->serv->address.proto,
-                        &state->ri.local_address);
-  } while (NULL != get_redirect_state (state->serv->address.af,
-                                      IPPROTO_UDP,
+    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,
                                       state->ri.remote_address.port,
                                       &state->ri.local_address.address,
                                       state->ri.local_address.port,
                                       &key));
+  {
+    char buf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Picked local address %s:%u for new connection\n",
+               inet_ntop (state->ri.local_address.af, 
+                          &state->ri.local_address.address,
+                          buf, sizeof (buf)),
+               (unsigned int) state->ri.local_address.port);
+  }
+  state->state_key = key;
   GNUNET_assert (GNUNET_OK ==
                 GNUNET_CONTAINER_multihashmap_put (connections_map, 
                                                    &key, state,
@@ -981,14 +1285,30 @@ setup_state_record (struct TunnelState *state)
 
 
 /**
- * FIXME: document
+ * Prepare an IPv4 packet for transmission via the TUN interface.
+ * Initializes the IP header and calculates checksums (IP+UDP/TCP).
+ * For UDP, the UDP header will be fully created, whereas for TCP
+ * only the ports and checksum will be filled in.  So for TCP,
+ * a skeleton TCP header must be part of the provided payload.
+ *
+ * @param payload payload of the packet (starting with UDP payload or
+ *                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 pkt4 where to write the assembled packet; must
+ *        contain enough space for the IP header, UDP/TCP header
+ *        AND the payload
  */
 static void
 prepare_ipv4_packet (const void *payload, size_t payload_length,
                     int protocol,
+                    const struct GNUNET_TUN_TcpHeader *tcp_header,
                     const struct SocketAddress *src_address,
                     const struct SocketAddress *dst_address,
-                    struct ip4_header *pkt4)
+                    struct GNUNET_TUN_IPv4Header *pkt4)
 {
   size_t len;
 
@@ -996,70 +1316,54 @@ prepare_ipv4_packet (const void *payload, size_t payload_length,
   switch (protocol)
   {
   case IPPROTO_UDP:
-    len += sizeof (struct udp_packet);
+    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 tcp_packet))
-    {
-      GNUNET_break (0);
-      return;
-    }
+    len += sizeof (struct GNUNET_TUN_TcpHeader);
+    GNUNET_assert (NULL != tcp_header);
     break;
   default:
     GNUNET_break (0);
     return;
   }
-  if (len + sizeof (struct ip4_header) > UINT16_MAX)
+  if (len + sizeof (struct GNUNET_TUN_IPv4Header) > UINT16_MAX)
   {
     GNUNET_break (0);
     return;
   }
 
-  pkt4->version = 4;
-  pkt4->header_length = sizeof (struct ip4_header) / 4;
-  pkt4->diff_serv = 0;
-  pkt4->total_length = htons ((uint16_t) (sizeof (struct ip4_header) + len));
-  pkt4->identification = (uint16_t) GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, 
-                                                             65536);
-  pkt4->flags = 0;
-  pkt4->fragmentation_offset = 0;
-  pkt4->ttl = 255;
-  pkt4->protocol = protocol;
-  pkt4->checksum = 0;
-  pkt4->destination_address = dst_address->address.ipv4;
-  pkt4->source_address = src_address->address.ipv4;
-  pkt4->checksum = GNUNET_CRYPTO_crc16_n (pkt4, sizeof (struct ip4_header));
-
+  GNUNET_TUN_initialize_ipv4_header (pkt4,
+                                    protocol,
+                                    len,
+                                    &src_address->address.ipv4,
+                                    &dst_address->address.ipv4);
   switch (protocol)
   {
   case IPPROTO_UDP:
     {
-      struct udp_packet *pkt4_udp = (struct udp_packet *) &pkt4[1];
+      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->crc = 0;  /* Optional for IPv4 */
+      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,
+                                         payload, payload_length);
       memcpy (&pkt4_udp[1], payload, payload_length);
     }
     break;
   case IPPROTO_TCP:
     {
-      struct tcp_packet *pkt4_tcp = (struct tcp_packet *) &pkt4[1];
+      struct GNUNET_TUN_TcpHeader *pkt4_tcp = (struct GNUNET_TUN_TcpHeader *) &pkt4[1];
       
-      memcpy (pkt4_tcp, payload, payload_length);
-      pkt4_tcp->spt = htons (src_address->port);
-      pkt4_tcp->dpt = htons (dst_address->port);
-      pkt4_tcp->crc = 0;
-      uint32_t sum = 0;
-      sum = GNUNET_CRYPTO_crc16_step (sum, 
-                                     &pkt4->source_address,
-                                     sizeof (struct in_addr) * 2);
-      uint32_t tmp = htonl ((protocol << 16) | (0xffff & len));
-      sum = GNUNET_CRYPTO_crc16_step (sum, & tmp, sizeof (uint32_t));
-      sum = GNUNET_CRYPTO_crc16_step (sum, & pkt4_tcp, len);
-      pkt4_tcp->crc = GNUNET_CRYPTO_crc16_finish (sum);
+      *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,
+                                         payload_length);
+      memcpy (&pkt4_tcp[1], payload, payload_length);
     }
     break;
   default:
@@ -1069,14 +1373,30 @@ prepare_ipv4_packet (const void *payload, size_t payload_length,
 
 
 /**
- * FIXME: document
+ * Prepare an IPv6 packet for transmission via the TUN interface.
+ * Initializes the IP header and calculates checksums (IP+UDP/TCP).
+ * For UDP, the UDP header will be fully created, whereas for TCP
+ * only the ports and checksum will be filled in.  So for TCP,
+ * a skeleton TCP header must be part of the provided payload.
+ *
+ * @param payload payload of the packet (starting with UDP payload or
+ *                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
+ *        contain enough space for the IP header, UDP/TCP header
+ *        AND the payload
  */
 static void
 prepare_ipv6_packet (const void *payload, size_t payload_length,
                     int protocol,
+                    const struct GNUNET_TUN_TcpHeader *tcp_header,
                     const struct SocketAddress *src_address,
                     const struct SocketAddress *dst_address,
-                    struct ip6_header *pkt6)
+                    struct GNUNET_TUN_IPv6Header *pkt6)
 {
   size_t len;
 
@@ -1084,15 +1404,10 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
   switch (protocol)
   {
   case IPPROTO_UDP:
-    len += sizeof (struct udp_packet);
+    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 tcp_packet))
-    {
-      GNUNET_break (0);
-      return;
-    }
+    len += sizeof (struct GNUNET_TUN_TcpHeader);
     break;
   default:
     GNUNET_break (0);
@@ -1104,55 +1419,41 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
     return;
   }
 
-  pkt6->version = 6;
-  pkt6->next_header = protocol;
-  pkt6->payload_length = htons ((uint16_t) (len + sizeof (struct ip6_header)));
-  pkt6->hop_limit = 255;
-  pkt6->destination_address = dst_address->address.ipv6;
-  pkt6->source_address = src_address->address.ipv6;
+  GNUNET_TUN_initialize_ipv6_header (pkt6,
+                                    protocol,
+                                    len,                                  
+                                    &src_address->address.ipv6,
+                                    &dst_address->address.ipv6);
 
   switch (protocol)
   {
   case IPPROTO_UDP:
     {
-      struct udp_packet *pkt6_udp = (struct udp_packet *) &pkt6[1];
+      struct GNUNET_TUN_UdpHeader *pkt6_udp = (struct GNUNET_TUN_UdpHeader *) &pkt6[1];
 
-      memcpy (&pkt6[1], payload, payload_length);
-      pkt6_udp->crc = 0;
-      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);
-
-      uint32_t sum = 0;
-      sum = GNUNET_CRYPTO_crc16_step (sum,
-                                     &pkt6->source_address,
-                                     sizeof (struct in6_addr) * 2);
-      uint32_t tmp = htons (len);
-      sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-      tmp = htonl (pkt6->next_header);
-      sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-      sum = GNUNET_CRYPTO_crc16_step (sum, pkt6_udp, len);
-      pkt6_udp->crc = GNUNET_CRYPTO_crc16_finish (sum);
+      GNUNET_TUN_calculate_udp6_checksum (pkt6,
+                                         pkt6_udp,
+                                         payload,
+                                         payload_length);
+      memcpy (&pkt6_udp[1], payload, payload_length);
     }
     break;
   case IPPROTO_TCP:
     {
-      struct tcp_packet *pkt6_tcp = (struct tcp_packet *) pkt6;
-      
-      memcpy (pkt6_tcp, payload, payload_length);
-      pkt6_tcp->crc = 0;
-      pkt6_tcp->spt = htons (src_address->port);
-      pkt6_tcp->dpt = htons (dst_address->port);
-
-      uint32_t sum = 0;
-      sum = GNUNET_CRYPTO_crc16_step (sum, &pkt6->source_address, 
-                                     sizeof (struct in6_addr) * 2);
-      uint32_t tmp = htonl (len);
-      sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));
-      tmp = htonl (pkt6->next_header);
-      sum = GNUNET_CRYPTO_crc16_step (sum, &tmp, sizeof (uint32_t));      
-      sum = GNUNET_CRYPTO_crc16_step (sum,  pkt6_tcp, len);
-      pkt6_tcp->crc = GNUNET_CRYPTO_crc16_finish (sum);
+      struct GNUNET_TUN_TcpHeader *pkt6_tcp = (struct GNUNET_TUN_TcpHeader *) &pkt6[1];
+
+      /* memcpy first here as some TCP header fields are initialized this way! */
+      *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:
@@ -1163,94 +1464,42 @@ prepare_ipv6_packet (const void *payload, size_t payload_length,
 
 
 /**
- * We've just experienced a connection in use.  Track it, or if it is
- * already tracked, update the tracking.
+ * Send a TCP packet via the TUN interface.
  *
- * @param u_i IP-level connection tracking state
- * @param tunnel associated mesh tunnel
- * @param desc service descriptor (or NULL)
- * @param serv service information
+ * @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 header template to use
+ * @param payload payload of the TCP packet
+ * @param payload_length number of bytes in 'payload'
  */
-void
-update_state_map (const struct RedirectInformation *ri,
-                 struct GNUNET_MESH_Tunnel *tunnel,
-                 const GNUNET_HashCode *desc,
-                 struct LocalService *serv)
+static void
+send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
+                        const struct SocketAddress *source_address,
+                        const struct GNUNET_TUN_TcpHeader *tcp_header,
+                        const void *payload, size_t payload_length)
 {
-  struct TunnelState *state;
-  GNUNET_HashCode state_key;
+  size_t len;
 
-  hash_redirect_info (&state_key,
-                     ri);
-  state = GNUNET_CONTAINER_multihashmap_get (connections_map, &state_key);
-  if (NULL == state)
-  {
-    state = GNUNET_malloc (sizeof (struct TunnelState));
-    state->tunnel = tunnel;
-    state->state_key = state_key;
-    state->serv = serv;
-    // FIXME? if (NULL != desc) state->desc = *desc;
-    // FIXME? state->redirect_info = *ri;
-    GNUNET_assert (GNUNET_OK ==
-                  GNUNET_CONTAINER_multihashmap_put (connections_map, &state_key, state,
-                                                     GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
-    state->heap_node =
-      GNUNET_CONTAINER_heap_insert (connections_heap,
-                                   state,
-                                   GNUNET_TIME_absolute_get ().abs_value);
-  }
-  else
-  {
-    if (state->tunnel != tunnel) 
-    {
-      /* Stats / warning: two tunnels got exactly the same connection state!? */
-      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-                 _("Two different mesh tunnels got the same connection state. Oops.\n"));
-      return;
-    }
-    GNUNET_CONTAINER_heap_update_cost (connections_heap,
-                                      state->heap_node,
-                                      GNUNET_TIME_absolute_get ().abs_value);
-  }
-  while (GNUNET_CONTAINER_heap_get_size (connections_heap) > max_connections)
-  {
-    state = GNUNET_CONTAINER_heap_remove_root (connections_heap);
-    state->heap_node = NULL;
-    GNUNET_MESH_tunnel_destroy (state->tunnel);
-    GNUNET_assert (GNUNET_OK ==
-                  GNUNET_CONTAINER_multihashmap_remove (connections_map,
-                                                        &state->state_key, 
-                                                        state));
-    GNUNET_free (state);
-  }
-}
-
-
-/**
- * FIXME: document!
- *
- * @param payload payload of the IP header (includes TCP header)
- */
-static void
-send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
-                        const struct SocketAddress *source_address,
-                        const void *payload, size_t payload_length)
-{
-  size_t len;
-
-  len = sizeof (struct GNUNET_MessageHeader) + sizeof (struct tun_header);
-  switch (source_address->af)
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# TCP packets sent via TUN"),
+                           1, GNUNET_NO);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Sending packet with %u bytes TCP 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 ip4_header);
+    len += sizeof (struct GNUNET_TUN_IPv4Header);
     break;
   case AF_INET6:
-    len += sizeof (struct ip6_header);
+    len += sizeof (struct GNUNET_TUN_IPv6Header);
     break;
   default:
     GNUNET_break (0);
     return;
   }
+  len += sizeof (struct GNUNET_TUN_TcpHeader);
   len += payload_length;
   if (len >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
   {
@@ -1258,23 +1507,25 @@ send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
     return;
   }
   {
-    char buf[len];
+    char buf[len] GNUNET_ALIGN;
     struct GNUNET_MessageHeader *hdr;
-    struct tun_header *tun;
+    struct GNUNET_TUN_Layer2PacketHeader *tun;
     
-    hdr= (struct GNUNET_MessageHeader *) buf;
-    hdr->type = htons (42);
+    hdr = (struct GNUNET_MessageHeader *) buf;
+    hdr->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
     hdr->size = htons (len);
-    tun = (struct tun_header*) &hdr[1];
+    tun = (struct GNUNET_TUN_Layer2PacketHeader*) &hdr[1];
     tun->flags = htons (0);
     switch (source_address->af)
     {
     case AF_INET:
       {
-       struct ip4_header * ipv4 = (struct ip4_header*) &tun[1];
+       struct GNUNET_TUN_IPv4Header * ipv4 = (struct GNUNET_TUN_IPv4Header*) &tun[1];
        
        tun->proto = htons (ETH_P_IPV4);
-       prepare_ipv4_packet (payload, payload_length, IPPROTO_TCP,
+       prepare_ipv4_packet (payload, payload_length,
+                            IPPROTO_TCP,
+                            tcp_header, 
                             source_address,
                             destination_address,
                             ipv4);
@@ -1282,10 +1533,12 @@ send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
       break;
     case AF_INET6:
       {
-       struct ip6_header * ipv6 = (struct ip6_header*) &tun[1];
+       struct GNUNET_TUN_IPv6Header * ipv6 = (struct GNUNET_TUN_IPv6Header*) &tun[1];
        
        tun->proto = htons (ETH_P_IPV6);
-       prepare_ipv6_packet (payload, payload_length, IPPROTO_TCP,
+       prepare_ipv6_packet (payload, payload_length, 
+                            IPPROTO_TCP,
+                            tcp_header, 
                             source_address,
                             destination_address,
                             ipv6);
@@ -1304,56 +1557,95 @@ send_tcp_packet_via_tun (const struct SocketAddress *destination_address,
 
 
 /**
- * The messages are one GNUNET_HashCode for the service followed by a struct tcp_packet
- * FIXME: document!
+ * Process a request via mesh to send a request to a TCP 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_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,
                      const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
 {
   struct TunnelState *state = *tunnel_ctx;
-  // FIXME: write proper request struct (we don't need the descriptor EACH time here!)
-  const GNUNET_HashCode *desc = (const GNUNET_HashCode *) &message[1];
-  const struct tcp_packet *pkt = (const struct tcp_packet *) &desc[1];
+  const struct GNUNET_EXIT_TcpServiceStartMessage *start;
   uint16_t pkt_len = ntohs (message->size);
 
-
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# TCP service creation requests received via mesh"),
+                           1, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
   /* check that we got at least a valid header */
-  if (pkt_len < sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode) + sizeof (struct tcp_packet))
+  if (pkt_len < sizeof (struct GNUNET_EXIT_TcpServiceStartMessage))
   {
     GNUNET_break_op (0);
-    return GNUNET_YES;
+    return GNUNET_SYSERR;
   }
-  pkt_len -= (sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode));
-
-  if (NULL == state->serv) 
+  start = (const struct GNUNET_EXIT_TcpServiceStartMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_TcpServiceStartMessage);
+  if ( (NULL == state) ||
+       (NULL != state->serv) ||
+       (NULL != state->heap_node) )
   {
-    /* setup fresh connection */
-    GNUNET_assert (NULL == state->heap_node);
-    if (NULL == (state->serv = find_service (tcp_services, desc, ntohs (pkt->dpt))))
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_INFO, 
-                 _("No service found for %s on port %d!\n"),
-                 "TCP",
-                 ntohs (pkt->dpt));
-      GNUNET_MESH_tunnel_destroy (state->tunnel);
-      return GNUNET_YES;
-    }
-    state->ri.remote_address = state->serv->address;    
-    setup_state_record (state);
+    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.destination_port));  
+  if (NULL == (state->serv = find_service (tcp_services, &start->service_descriptor, 
+                                          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.destination_port));
+    GNUNET_STATISTICS_update (stats,
+                             gettext_noop ("# TCP requests dropped (no such service)"),
+                             1, GNUNET_NO);
+    return GNUNET_SYSERR;
+  }
+  state->ri.remote_address = state->serv->address;    
+  setup_state_record (state);
   send_tcp_packet_via_tun (&state->ri.remote_address,
                           &state->ri.local_address,
-                          pkt, pkt_len);
+                          &start->tcp_header,
+                          &start[1], pkt_len);
   return GNUNET_YES;
 }
 
 
 /**
- * FIXME: document!
+ * Process a request to forward TCP 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_tcp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
@@ -1363,36 +1655,765 @@ receive_tcp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                     const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
 {
   struct TunnelState *state = *tunnel_ctx;
-  // FIXME: write proper request struct (!)
-  const GNUNET_HashCode *desc = (const GNUNET_HashCode *) &message[1];
-  const struct tcp_packet *pkt = (const struct tcp_packet *) &desc[1];
-  const struct SocketAddress *s = (const struct SocketAddress *) desc;
+  const struct GNUNET_EXIT_TcpInternetStartMessage *start;
   uint16_t pkt_len = ntohs (message->size);
+  const struct in_addr *v4;
+  const struct in6_addr *v6;
+  const void *payload;
+  int af;
 
-  if (pkt_len < sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode) + sizeof (struct tcp_packet))
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# TCP IP-exit creation requests received via mesh"),
+                           1, GNUNET_NO);
+  if (pkt_len < sizeof (struct GNUNET_EXIT_TcpInternetStartMessage))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  start = (const struct GNUNET_EXIT_TcpInternetStartMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_TcpInternetStartMessage);  
+  if ( (NULL == state) ||
+       (NULL != state->serv) ||
+       (NULL != state->heap_node) )
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (start->tcp_header.off * 4 < sizeof (struct GNUNET_TUN_TcpHeader))
   {
     GNUNET_break_op (0);
-    return GNUNET_YES;
+    return GNUNET_SYSERR;
   }
-  pkt_len -= (sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode));
+  af = (int) ntohl (start->af);
+  state->ri.remote_address.af = af;
+  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*) &start[1];
+    payload = &v4[1];
+    pkt_len -= sizeof (struct in_addr);
+    state->ri.remote_address.address.ipv4 = *v4;
+    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*) &start[1];
+    payload = &v6[1];
+    pkt_len -= sizeof (struct in6_addr);
+    state->ri.remote_address.address.ipv6 = *v6;
+    break;
+  default:
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  {
+    char buf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Received data from %s for starting TCP stream to %s:%u\n",
+               GNUNET_i2s (sender),
+               inet_ntop (af, 
+                          &state->ri.remote_address.address,
+                          buf, sizeof (buf)),
+               (unsigned int) ntohs (start->tcp_header.destination_port));  
+  }
+  state->ri.remote_address.proto = IPPROTO_TCP;
+  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,
+                          &start->tcp_header,
+                          payload, pkt_len);
+  return GNUNET_YES;
+}
 
-  if (NULL == state->heap_node)
+
+/**
+ * Process a request to forward TCP data on an established 
+ * connection 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_tcp_data (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_TcpDataMessage *data;
+  uint16_t pkt_len = ntohs (message->size);
+
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# TCP data requests received via mesh"),
+                           1, GNUNET_NO);
+  if (pkt_len < sizeof (struct GNUNET_EXIT_TcpDataMessage))
   {
-    /* first packet, setup record */
-    state->ri.remote_address = *s;
-    setup_state_record (state);
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  data = (const struct GNUNET_EXIT_TcpDataMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_TcpDataMessage);  
+  if ( (NULL == state) ||
+       (NULL == state->heap_node) )
+  {
+    /* connection should have been up! */
+    GNUNET_STATISTICS_update (stats,
+                             gettext_noop ("# TCP DATA requests dropped (no session)"),
+                             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 %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,
+                          buf, sizeof (buf)),
+               (unsigned int) state->ri.remote_address.port);
   }
 
   send_tcp_packet_via_tun (&state->ri.remote_address,
                           &state->ri.local_address,
-                          pkt, pkt_len);
+                          &data->tcp_header,
+                          &data[1], pkt_len);
   return GNUNET_YES;
 }
 
 
 /**
- * FIXME: document!
+ * Send an ICMP packet via the TUN interface.
+ *
+ * @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_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 ("# ICMP packets sent via TUN"),
+                           1, GNUNET_NO);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "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 (destination_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_IcmpHeader);
+  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);
+       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:
+      {
+       struct GNUNET_TUN_IPv6Header * ipv6 = (struct GNUNET_TUN_IPv6Header*) &tun[1];
+       
+       tun->proto = htons (ETH_P_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,
+                              NULL, NULL);
+  }
+}
+
+
+/**
+ * Synthesize a plausible ICMP payload for an ICMPv4 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_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,
@@ -1401,20 +2422,26 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
 {
   size_t len;
 
-  len = sizeof (struct GNUNET_MessageHeader) + sizeof (struct tun_header);
+  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 ip4_header);
+    len += sizeof (struct GNUNET_TUN_IPv4Header);
     break;
   case AF_INET6:
-    len += sizeof (struct ip6_header);
+    len += sizeof (struct GNUNET_TUN_IPv6Header);
     break;
   default:
     GNUNET_break (0);
     return;
   }
-  len += sizeof (struct udp_packet);
+  len += sizeof (struct GNUNET_TUN_UdpHeader);
   len += payload_length;
   if (len >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
   {
@@ -1422,23 +2449,25 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
     return;
   }
   {
-    char buf[len];
+    char buf[len] GNUNET_ALIGN;
     struct GNUNET_MessageHeader *hdr;
-    struct tun_header *tun;
+    struct GNUNET_TUN_Layer2PacketHeader *tun;
     
     hdr= (struct GNUNET_MessageHeader *) buf;
-    hdr->type = htons (42);
+    hdr->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER);
     hdr->size = htons (len);
-    tun = (struct tun_header*) &hdr[1];
+    tun = (struct GNUNET_TUN_Layer2PacketHeader*) &hdr[1];
     tun->flags = htons (0);
     switch (source_address->af)
     {
     case AF_INET:
       {
-       struct ip4_header * ipv4 = (struct ip4_header*) &tun[1];
+       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,
+       prepare_ipv4_packet (payload, payload_length,
+                            IPPROTO_UDP,
+                            NULL,
                             source_address,
                             destination_address,
                             ipv4);
@@ -1446,10 +2475,12 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
       break;
     case AF_INET6:
       {
-       struct ip6_header * ipv6 = (struct ip6_header*) &tun[1];
+       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,
+       prepare_ipv6_packet (payload, payload_length, 
+                            IPPROTO_UDP,
+                            NULL,
                             source_address,
                             destination_address,
                             ipv6);
@@ -1468,7 +2499,16 @@ send_udp_packet_via_tun (const struct SocketAddress *destination_address,
 
 
 /**
- * FIXME: document!
+ * 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
 receive_udp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
@@ -1478,35 +2518,101 @@ receive_udp_remote (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                     const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
 {
   struct TunnelState *state = *tunnel_ctx;
-  // FIXME: write proper request struct (!)
-  const GNUNET_HashCode *desc = (const GNUNET_HashCode *) &message[1];
-  const struct udp_packet *pkt = (const struct udp_packet *) &desc[1];
-  const struct SocketAddress *s = (const struct SocketAddress *) desc;
+  const struct GNUNET_EXIT_UdpInternetMessage *msg;
   uint16_t pkt_len = ntohs (message->size);
+  const struct in_addr *v4;
+  const struct in6_addr *v6;
+  const void *payload;
+  int af;
 
-  if (pkt_len < sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode) + sizeof (struct udp_packet))
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# UDP IP-exit requests received via mesh"),
+                           1, GNUNET_NO);
+  if (pkt_len < sizeof (struct GNUNET_EXIT_UdpInternetMessage))
   {
     GNUNET_break_op (0);
-    return GNUNET_YES;
+    return GNUNET_SYSERR;
   }
-  pkt_len -= (sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode));
-
-  if (NULL == state->heap_node)
+  msg = (const struct GNUNET_EXIT_UdpInternetMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_UdpInternetMessage);  
+  af = (int) ntohl (msg->af);
+  state->ri.remote_address.af = af;
+  switch (af)
   {
-    /* first packet, setup record */
-    state->ri.remote_address = *s;
-    setup_state_record (state);
+  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;
+    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;
+    break;
+  default:
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
   }
-
+  {
+    char buf[INET6_ADDRSTRLEN];
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+               "Received data from %s for forwarding to UDP %s:%u\n",
+               GNUNET_i2s (sender),
+               inet_ntop (af, 
+                          &state->ri.remote_address.address,
+                          buf, sizeof (buf)),
+               (unsigned int) ntohs (msg->destination_port));  
+  }
+  state->ri.remote_address.proto = IPPROTO_UDP;
+  state->ri.remote_address.port = msg->destination_port;
+  if (NULL == state->heap_node)
+    setup_state_record (state);
+  if (0 != ntohs (msg->source_port))
+    state->ri.local_address.port = msg->source_port;
   send_udp_packet_via_tun (&state->ri.remote_address,
                           &state->ri.local_address,
-                          &pkt[1], pkt_len - sizeof (struct udp_packet));
+                          payload, pkt_len);
   return GNUNET_YES;
 }
 
 
 /**
- * FIXME: document!
+ * Process a request via mesh to send a request to a UDP 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_udp_service (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
@@ -1516,43 +2622,47 @@ receive_udp_service (void *cls GNUNET_UNUSED, struct GNUNET_MESH_Tunnel *tunnel,
                      const struct GNUNET_ATS_Information *atsi GNUNET_UNUSED)
 {
   struct TunnelState *state = *tunnel_ctx;
-  // FIXME: write proper request struct (we don't need UDP except dpt either!)
-  const GNUNET_HashCode *desc = (const GNUNET_HashCode *) &message[1];
-  const struct udp_packet *pkt = (const struct udp_packet *) &desc[1];
+  const struct GNUNET_EXIT_UdpServiceMessage *msg;
   uint16_t pkt_len = ntohs (message->size);
 
-
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Bytes received from MESH"),
+                           pkt_len, GNUNET_NO);
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# UDP service requests received via mesh"),
+                           1, GNUNET_NO);
   /* check that we got at least a valid header */
-  if (pkt_len < sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode) + sizeof (struct udp_packet))
+  if (pkt_len < sizeof (struct GNUNET_EXIT_UdpServiceMessage))
   {
     GNUNET_break_op (0);
-    return GNUNET_YES;
+    return GNUNET_SYSERR;
   }
-  pkt_len -= (sizeof (struct GNUNET_MessageHeader) + sizeof (GNUNET_HashCode));
-
-  GNUNET_assert (ntohs (pkt->len) ==
-                 ntohs (message->size) - sizeof (struct GNUNET_MessageHeader) -
-                 sizeof (GNUNET_HashCode));
-
-  if (NULL == state->serv) 
+  msg = (const struct GNUNET_EXIT_UdpServiceMessage*) message;
+  pkt_len -= sizeof (struct GNUNET_EXIT_UdpServiceMessage);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Received data from %s for forwarding to UDP service %s on port %u\n",
+             GNUNET_i2s (sender),
+             GNUNET_h2s (&msg->service_descriptor),
+             (unsigned int) ntohs (msg->destination_port));  
+  if (NULL == (state->serv = find_service (udp_services, &msg->service_descriptor, 
+                                          ntohs (msg->destination_port))))
   {
-    /* setup fresh connection */
-    GNUNET_assert (NULL == state->heap_node);
-    if (NULL == (state->serv = find_service (udp_services, desc, ntohs (pkt->dpt))))
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_INFO, 
-                 _("No service found for %s on port %d!\n"),
-                 "UDP",
-                 ntohs (pkt->dpt));
-      GNUNET_MESH_tunnel_destroy (state->tunnel);
-      return GNUNET_YES;
-    }
-    state->ri.remote_address = state->serv->address;    
-    setup_state_record (state);
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO, 
+               _("No service found for %s on port %d!\n"),
+               "UDP",
+               ntohs (msg->destination_port));
+    GNUNET_STATISTICS_update (stats,
+                             gettext_noop ("# UDP requests dropped (no such service)"),
+                             1, GNUNET_NO);
+    return GNUNET_SYSERR;
   }
+  state->ri.remote_address = state->serv->address;    
+  setup_state_record (state);
+  if (0 != ntohs (msg->source_port))
+    state->ri.local_address.port = msg->source_port;
   send_udp_packet_via_tun (&state->ri.remote_address,
                           &state->ri.local_address,
-                          &pkt[1], pkt_len - sizeof (struct udp_packet));
+                          &msg[1], pkt_len);
   return GNUNET_YES;
 }
 
@@ -1569,10 +2679,16 @@ 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));
-  
+
+  GNUNET_STATISTICS_update (stats,
+                           gettext_noop ("# Inbound MESH tunnels created"),
+                           1, GNUNET_NO);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Received inbound tunnel from `%s'\n",
+             GNUNET_i2s (initiator));
   s->tunnel = tunnel;
   return s;
 }
@@ -1594,6 +2710,8 @@ clean_tunnel (void *cls GNUNET_UNUSED, const struct GNUNET_MESH_Tunnel *tunnel,
   struct TunnelState *s = tunnel_ctx;
   struct TunnelMessageQueue *tnq;
 
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Tunnel destroyed\n");
   while (NULL != (tnq = s->head))
   {
     GNUNET_CONTAINER_DLL_remove (s->head,
@@ -1628,7 +2746,7 @@ clean_tunnel (void *cls GNUNET_UNUSED, const struct GNUNET_MESH_Tunnel *tunnel,
  */
 static int
 free_iterate (void *cls GNUNET_UNUSED,
-              const GNUNET_HashCode * hash GNUNET_UNUSED, void *value)
+              const struct GNUNET_HashCode * hash GNUNET_UNUSED, void *value)
 {
   GNUNET_free (value);
   return GNUNET_YES;
@@ -1644,6 +2762,8 @@ cleanup (void *cls GNUNET_UNUSED,
 {
   unsigned int i;
 
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+             "Exit service is shutting down now\n");
   if (helper_handle != NULL)
   {
     GNUNET_HELPER_stop (helper_handle);
@@ -1677,7 +2797,12 @@ cleanup (void *cls GNUNET_UNUSED,
     GNUNET_CONTAINER_multihashmap_destroy (udp_services);
     udp_services = NULL;
   }
-  for (i=0;i<5;i++)
+  if (stats != NULL)
+  {
+    GNUNET_STATISTICS_destroy (stats, GNUNET_NO);
+    stats = NULL;
+  }
+  for (i=0;i<8;i++)
     GNUNET_free_non_null (exit_argv[i]);
 }
 
@@ -1742,18 +2867,19 @@ add_services (int proto,
     }
 
     serv = GNUNET_malloc (sizeof (struct LocalService));
+    serv->address.proto = proto;
     serv->my_port = (uint16_t) local_port;
     serv->address.port = remote_port;
     if (0 == strcmp ("localhost4", hostname))
     {
-      const char *ip4addr = exit_argv[4];
+      const char *ip4addr = exit_argv[5];
 
       serv->address.af = AF_INET;      
-      GNUNET_assert (1 != inet_pton (AF_INET, ip4addr, &serv->address.address.ipv4));
+      GNUNET_assert (1 == inet_pton (AF_INET, ip4addr, &serv->address.address.ipv4));
     }
     else if (0 == strcmp ("localhost6", hostname))
     {
-      const char *ip6addr = exit_argv[2];
+      const char *ip6addr = exit_argv[3];
 
       serv->address.af = AF_INET6;
       GNUNET_assert (1 == inet_pton (AF_INET6, ip6addr, &serv->address.address.ipv6));
@@ -1777,12 +2903,30 @@ add_services (int proto,
       serv->address.af = res->ai_family;
       switch (res->ai_family)
       {
-       case AF_INET:
-         serv->address.address.ipv4 = ((struct sockaddr_in *) res->ai_addr)->sin_addr;
-         break;
-       case AF_INET6:
-         serv->address.address.ipv6 = ((struct sockaddr_in6 *) res->ai_addr)->sin6_addr;
-         break;
+      case AF_INET:
+       if (! ipv4_enabled)
+       {
+         GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                     _("Service `%s' configured for IPv4, but IPv4 is disabled!\n"),
+                     name);
+         freeaddrinfo (res);
+         GNUNET_free (serv);
+         continue;
+       }
+       serv->address.address.ipv4 = ((struct sockaddr_in *) res->ai_addr)->sin_addr;
+       break;
+      case AF_INET6:
+       if (! ipv6_enabled)
+       {
+         GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                     _("Service `%s' configured for IPv4, but IPv4 is disabled!\n"),
+                     name);
+         freeaddrinfo (res);
+         GNUNET_free (serv);
+         continue;
+       }       
+       serv->address.address.ipv6 = ((struct sockaddr_in6 *) res->ai_addr)->sin6_addr;
+       break;
       default:
        freeaddrinfo (res);
        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
@@ -1847,10 +2991,13 @@ run (void *cls, char *const *args GNUNET_UNUSED,
      const struct GNUNET_CONFIGURATION_Handle *cfg_)
 {
   static struct GNUNET_MESH_MessageHandler handlers[] = {
-    {&receive_udp_service, GNUNET_MESSAGE_TYPE_VPN_SERVICE_UDP, 0},
-    {&receive_tcp_service, GNUNET_MESSAGE_TYPE_VPN_SERVICE_TCP, 0},
-    {NULL, 0, 0},
-    {NULL, 0, 0},
+    {&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_TO_EXIT, 0},
     {NULL, 0, 0}
   };
 
@@ -1859,120 +3006,196 @@ run (void *cls, char *const *args GNUNET_UNUSED,
     GNUNET_APPLICATION_TYPE_END,
     GNUNET_APPLICATION_TYPE_END
   };
-  unsigned int handler_idx;
   unsigned int app_idx;
-  int udp;
-  int tcp;
-  char *ifname;
+  char *exit_ifname;
+  char *tun_ifname;
   char *ipv6addr;
   char *ipv6prefix_s;
   char *ipv4addr;
   char *ipv4mask;
-  struct in_addr v4;
-  struct in6_addr v6;
+  char *binary;
+  char *regex;
 
-  cfg = cfg_;
-  GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_FOREVER_REL, &cleanup, cls);
-  if (GNUNET_OK !=
-      GNUNET_CONFIGURATION_get_value_number (cfg, "exit", "MAX_CONNECTIONS",
-                                             &max_connections))
-    max_connections = 1024;
-  exit_argv[0] = GNUNET_strdup ("exit-gnunet");
-  if (GNUNET_SYSERR ==
-      GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IFNAME", &ifname))
+  binary = GNUNET_OS_get_libexec_binary_path ("gnunet-helper-exit");
+  if (GNUNET_YES !=
+      GNUNET_OS_check_helper_binary (binary))
   {
+    GNUNET_free (binary);
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No entry 'IFNAME' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
+               _("`%s' must be installed SUID, refusing to run\n"),
+               "gnunet-helper-exit");
+    global_ret = 1;
     return;
   }
-  exit_argv[1] = ifname;
-  if ( (GNUNET_SYSERR ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV6ADDR",
-                                              &ipv6addr) ||
-       (1 != inet_pton (AF_INET6, ipv6addr, &v6))) )
+  GNUNET_free (binary);
+  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 != GNUNET_NETWORK_test_pf (PF_INET))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No valid entry 'IPV6ADDR' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+               _("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;
   }
-  exit_argv[2] = ipv6addr;
-  if (GNUNET_SYSERR ==
-      GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV6PREFIX",
-                                             &ipv6prefix_s))
+  if ( (ipv6_exit || ipv6_enabled) &&
+       GNUNET_OK != GNUNET_NETWORK_test_pf (PF_INET6))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No entry 'IPV6PREFIX' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+               _("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;
   }
-  exit_argv[3] = ipv6prefix_s;
-  if ( (GNUNET_OK !=
-       GNUNET_CONFIGURATION_get_value_number (cfg, "exit",
-                                              "IPV6PREFIX",
-                                              &ipv6prefix)) ||
-       (ipv6prefix >= 127) )
+  if (ipv4_exit && (! ipv4_enabled))
   {
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+               _("Cannot enable IPv4 exit but disable IPv4 on TUN interface, will use ENABLE_IPv4=YES\n"));
+    ipv4_enabled = GNUNET_YES;
   }
-
-  if ( (GNUNET_SYSERR ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV4ADDR",
-                                              &ipv4addr) ||
-       (1 != inet_pton (AF_INET, ipv4addr, &v4))) )
+  if (ipv6_exit && (! ipv6_enabled))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No valid entry for 'IPV4ADDR' in configuration!\n");
-    GNUNET_SCHEDULER_shutdown ();
-    return;
+               _("Cannot enable IPv6 exit but disable IPv6 on TUN interface, will use ENABLE_IPv6=YES\n"));
+    ipv6_enabled = GNUNET_YES;
   }
-  exit_argv[4] = ipv4addr;
-  if ( (GNUNET_SYSERR ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV4MASK",
-                                              &ipv4mask) ||
-       (1 != inet_pton (AF_INET, ipv4mask, &v4))) )
+  if (! (ipv4_enabled || ipv6_enabled))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "No valid entry 'IPV4MASK' in configuration!\n");
+               _("No useful service enabled.  Exiting.\n"));
     GNUNET_SCHEDULER_shutdown ();
-    return;
+    return;    
   }
-  exit_argv[5] = ipv4mask;
-  exit_argv[6] = NULL;
-
   app_idx = 0;
-  handler_idx = 2;
-  udp = GNUNET_CONFIGURATION_get_value_yesno (cfg, "exit", "ENABLE_UDP");
-  tcp = GNUNET_CONFIGURATION_get_value_yesno (cfg, "exit", "ENABLE_TCP");
-  if (GNUNET_YES == udp)
-  {
-    handlers[handler_idx].callback = &receive_udp_remote;
-    handlers[handler_idx].expected_size = 0;
-    handlers[handler_idx].type = GNUNET_MESSAGE_TYPE_VPN_REMOTE_UDP;
-    apptypes[app_idx] = GNUNET_APPLICATION_TYPE_INTERNET_UDP_GATEWAY;
-    handler_idx++;
+  if (GNUNET_YES == ipv4_exit)    
+  {
+    apptypes[app_idx] = GNUNET_APPLICATION_TYPE_IPV4_GATEWAY;
     app_idx++;
   }
-
-  if (GNUNET_YES == tcp)
+  if (GNUNET_YES == ipv6_exit)    
   {
-    handlers[handler_idx].callback = &receive_tcp_remote;
-    handlers[handler_idx].expected_size = 0;
-    handlers[handler_idx].type = GNUNET_MESSAGE_TYPE_VPN_REMOTE_TCP;
-    apptypes[app_idx] = GNUNET_APPLICATION_TYPE_INTERNET_TCP_GATEWAY;
-    handler_idx++;
+    apptypes[app_idx] = GNUNET_APPLICATION_TYPE_IPV6_GATEWAY;
     app_idx++;
   }
-  udp_services = GNUNET_CONTAINER_multihashmap_create (65536);
-  tcp_services = GNUNET_CONTAINER_multihashmap_create (65536);
+
+  GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_FOREVER_REL, &cleanup, cls);
+
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_number (cfg, "exit", "MAX_CONNECTIONS",
+                                             &max_connections))
+    max_connections = 1024;
+  exit_argv[0] = GNUNET_strdup ("exit-gnunet");
+  if (GNUNET_SYSERR ==
+      GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "TUN_IFNAME", &tun_ifname))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "No entry 'TUN_IFNAME' in configuration!\n");
+    GNUNET_SCHEDULER_shutdown ();
+    return;
+  }
+  exit_argv[1] = tun_ifname;
+  if (ipv4_enabled)
+  {
+    if (GNUNET_SYSERR ==
+       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "EXIT_IFNAME", &exit_ifname))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No entry 'EXIT_IFNAME' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    exit_argv[2] = exit_ifname;
+  }
+  else
+  {
+    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, &exit_ipv6addr))) )
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No valid entry 'IPV6ADDR' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    exit_argv[3] = ipv6addr;
+    if (GNUNET_SYSERR ==
+       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV6PREFIX",
+                                              &ipv6prefix_s))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No entry 'IPV6PREFIX' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    exit_argv[4] = ipv6prefix_s;
+    if ( (GNUNET_OK !=
+         GNUNET_CONFIGURATION_get_value_number (cfg, "exit",
+                                                "IPV6PREFIX",
+                                                &ipv6prefix)) ||
+        (ipv6prefix >= 127) )
+    {
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+  } 
+  else
+  {
+    /* IPv6 explicitly disabled */
+    exit_argv[3] = GNUNET_strdup ("-");
+    exit_argv[4] = GNUNET_strdup ("-");
+  }
+  if (GNUNET_YES == ipv4_enabled)
+  {
+    if ( (GNUNET_SYSERR ==
+         GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV4ADDR",
+                                                &ipv4addr) ||
+         (1 != inet_pton (AF_INET, ipv4addr, &exit_ipv4addr))) )
+      {
+       GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                   "No valid entry for 'IPV4ADDR' in configuration!\n");
+       GNUNET_SCHEDULER_shutdown ();
+       return;
+      }
+    exit_argv[5] = ipv4addr;
+    if ( (GNUNET_SYSERR ==
+         GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "IPV4MASK",
+                                                &ipv4mask) ||
+         (1 != inet_pton (AF_INET, ipv4mask, &exit_ipv4mask))) )
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                 "No valid entry 'IPV4MASK' in configuration!\n");
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    exit_argv[6] = ipv4mask;
+  }
+  else
+  {
+    /* IPv4 explicitly disabled */
+    exit_argv[5] = GNUNET_strdup ("-");
+    exit_argv[6] = GNUNET_strdup ("-");
+  }
+  exit_argv[7] = NULL;
+
+  udp_services = GNUNET_CONTAINER_multihashmap_create (65536, GNUNET_NO);
+  tcp_services = GNUNET_CONTAINER_multihashmap_create (65536, GNUNET_NO);
   GNUNET_CONFIGURATION_iterate_sections (cfg, &read_service_conf, NULL);
 
-  connections_map = GNUNET_CONTAINER_multihashmap_create (65536);
+  connections_map = GNUNET_CONTAINER_multihashmap_create (65536, GNUNET_NO);
   connections_heap = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
   mesh_handle 
-    = GNUNET_MESH_connect (cfg, 42 /* queue size */, NULL, 
+    = GNUNET_MESH_connect (cfg, NULL, 
                           &new_tunnel, 
                           &clean_tunnel, handlers,
                            apptypes);
@@ -1981,9 +3204,31 @@ run (void *cls, char *const *args GNUNET_UNUSED,
     GNUNET_SCHEDULER_shutdown ();
     return;
   }
-  helper_handle = GNUNET_HELPER_start ("gnunet-helper-vpn", 
+
+  /* Mesh handle acquired, now announce regular expressions matching our exit */
+  if ( (GNUNET_YES == ipv4_enabled) && (GNUNET_YES == ipv4_exit) )
+  {
+    if (GNUNET_OK !=
+       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "EXIT_RANGE_IPV4_REGEX", &regex))
+      regex = GNUNET_strdup ("(0|1)*");
+    GNUNET_MESH_announce_regex (mesh_handle, regex, REGEX_MAX_PATH_LEN_IPV4);
+    GNUNET_free (regex);
+  }
+
+  if (GNUNET_YES == ipv6_enabled && GNUNET_YES == ipv6_exit)
+  {
+    if (GNUNET_OK !=
+       GNUNET_CONFIGURATION_get_value_string (cfg, "exit", "EXIT_RANGE_IPV6_REGEX", &regex))
+      regex = GNUNET_strdup ("(0|1)*");
+    GNUNET_MESH_announce_regex (mesh_handle, regex, REGEX_MAX_PATH_LEN_IPV6);
+    GNUNET_free (regex);
+  }
+
+  helper_handle = GNUNET_HELPER_start (GNUNET_NO,
+                                      "gnunet-helper-exit", 
                                       exit_argv,
-                                      &message_token, NULL);
+                                      &message_token,
+                                      NULL, NULL);
 }
 
 
@@ -2001,11 +3246,14 @@ main (int argc, char *const *argv)
     GNUNET_GETOPT_OPTION_END
   };
 
+  if (GNUNET_OK != GNUNET_STRINGS_get_utf8_args (argc, argv, &argc, &argv))
+    return 2;
+
   return (GNUNET_OK ==
           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;
 }