NAT: Rename snat plugin to nat (VPP-955)

Change-Id: I30a7e3da7a4efc6038a91e27b48045d4b07e2764
Signed-off-by: Matus Fabian <matfabia@cisco.com>

1 files changed, 858 insertions, 0 deletions

diff --git a/src/plugins/nat/nat64.c b/src/plugins/nat/nat64.c
new file mode 100644
index 00000000000..b04901fade4
--- /dev/null
+++ b/src/plugins/nat/nat64.c
@@ -0,0 +1,858 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * @file
+ * @brief NAT64 implementation
+ */
+
+#include <nat/nat64.h>
+#include <nat/nat64_db.h>
+#include <vnet/fib/ip4_fib.h>
+
+
+nat64_main_t nat64_main;
+
+/* *INDENT-OFF* */
+
+/* Hook up input features */
+VNET_FEATURE_INIT (nat64_in2out, static) = {
+  .arc_name = "ip6-unicast",
+  .node_name = "nat64-in2out",
+  .runs_before = VNET_FEATURES ("ip6-lookup"),
+};
+VNET_FEATURE_INIT (nat64_out2in, static) = {
+  .arc_name = "ip4-unicast",
+  .node_name = "nat64-out2in",
+  .runs_before = VNET_FEATURES ("ip4-lookup"),
+};
+
+static u8 well_known_prefix[] = {
+  0x00, 0x64, 0xff, 0x9b,
+  0x00, 0x00, 0x00, 0x00,
+  0x00, 0x00, 0x00, 0x00,
+  0x00, 0x00, 0x00, 0x00
+};
+
+/* *INDENT-ON* */
+
+clib_error_t *
+nat64_init (vlib_main_t * vm)
+{
+  nat64_main_t *nm = &nat64_main;
+  clib_error_t *error = 0;
+  vlib_thread_main_t *tm = vlib_get_thread_main ();
+
+  nm->is_disabled = 0;
+
+  if (tm->n_vlib_mains > 1)
+    {
+      nm->is_disabled = 1;
+      goto error;
+    }
+
+  if (nat64_db_init (&nm->db))
+    {
+      error = clib_error_return (0, "NAT64 DB init failed");
+      goto error;
+    }
+
+  /* set session timeouts to default values */
+  nm->udp_timeout = SNAT_UDP_TIMEOUT;
+  nm->icmp_timeout = SNAT_ICMP_TIMEOUT;
+  nm->tcp_trans_timeout = SNAT_TCP_TRANSITORY_TIMEOUT;
+  nm->tcp_est_timeout = SNAT_TCP_ESTABLISHED_TIMEOUT;
+  nm->tcp_incoming_syn_timeout = SNAT_TCP_INCOMING_SYN;
+
+error:
+  return error;
+}
+
+int
+nat64_add_del_pool_addr (ip4_address_t * addr, u32 vrf_id, u8 is_add)
+{
+  nat64_main_t *nm = &nat64_main;
+  snat_address_t *a = 0;
+  snat_interface_t *interface;
+  int i;
+
+  /* Check if address already exists */
+  for (i = 0; i < vec_len (nm->addr_pool); i++)
+    {
+      if (nm->addr_pool[i].addr.as_u32 == addr->as_u32)
+	{
+	  a = nm->addr_pool + i;
+	  break;
+	}
+    }
+
+  if (is_add)
+    {
+      if (a)
+	return VNET_API_ERROR_VALUE_EXIST;
+
+      vec_add2 (nm->addr_pool, a, 1);
+      a->addr = *addr;
+      a->fib_index = 0;
+      if (vrf_id != ~0)
+	a->fib_index =
+	  fib_table_find_or_create_and_lock (FIB_PROTOCOL_IP6, vrf_id);
+#define _(N, i, n, s) \
+      clib_bitmap_alloc (a->busy_##n##_port_bitmap, 65535);
+      foreach_snat_protocol
+#undef _
+    }
+  else
+    {
+      if (!a)
+	return VNET_API_ERROR_NO_SUCH_ENTRY;
+
+      if (a->fib_index)
+	fib_table_unlock (a->fib_index, FIB_PROTOCOL_IP6);
+
+#define _(N, id, n, s) \
+      clib_bitmap_free (a->busy_##n##_port_bitmap);
+      foreach_snat_protocol
+#undef _
+	/* Delete sessions using address */
+	nat64_db_free_out_addr (&nm->db, &a->addr);
+      vec_del1 (nm->addr_pool, i);
+    }
+
+  /* Add/del external address to FIB */
+  /* *INDENT-OFF* */
+  pool_foreach (interface, nm->interfaces,
+  ({
+    if (interface->is_inside)
+      continue;
+
+    snat_add_del_addr_to_fib (addr, 32, interface->sw_if_index, is_add);
+    break;
+  }));
+  /* *INDENT-ON* */
+
+  return 0;
+}
+
+void
+nat64_pool_addr_walk (nat64_pool_addr_walk_fn_t fn, void *ctx)
+{
+  nat64_main_t *nm = &nat64_main;
+  snat_address_t *a = 0;
+
+  /* *INDENT-OFF* */
+  vec_foreach (a, nm->addr_pool)
+    {
+      if (fn (a, ctx))
+        break;
+    };
+  /* *INDENT-ON* */
+}
+
+int
+nat64_add_del_interface (u32 sw_if_index, u8 is_inside, u8 is_add)
+{
+  nat64_main_t *nm = &nat64_main;
+  snat_interface_t *interface = 0, *i;
+  snat_address_t *ap;
+  const char *feature_name, *arc_name;
+
+  /* Check if address already exists */
+  /* *INDENT-OFF* */
+  pool_foreach (i, nm->interfaces,
+  ({
+    if (i->sw_if_index == sw_if_index)
+      {
+        interface = i;
+        break;
+      }
+  }));
+  /* *INDENT-ON* */
+
+  if (is_add)
+    {
+      if (interface)
+	return VNET_API_ERROR_VALUE_EXIST;
+
+      pool_get (nm->interfaces, interface);
+      interface->sw_if_index = sw_if_index;
+      interface->is_inside = is_inside;
+
+    }
+  else
+    {
+      if (!interface)
+	return VNET_API_ERROR_NO_SUCH_ENTRY;
+
+      pool_put (nm->interfaces, interface);
+    }
+
+  if (!is_inside)
+    {
+      /* *INDENT-OFF* */
+      vec_foreach (ap, nm->addr_pool)
+        snat_add_del_addr_to_fib(&ap->addr, 32, sw_if_index, is_add);
+      /* *INDENT-ON* */
+    }
+
+  arc_name = is_inside ? "ip6-unicast" : "ip4-unicast";
+  feature_name = is_inside ? "nat64-in2out" : "nat64-out2in";
+
+  return vnet_feature_enable_disable (arc_name, feature_name, sw_if_index,
+				      is_add, 0, 0);
+}
+
+void
+nat64_interfaces_walk (nat64_interface_walk_fn_t fn, void *ctx)
+{
+  nat64_main_t *nm = &nat64_main;
+  snat_interface_t *i = 0;
+
+  /* *INDENT-OFF* */
+  pool_foreach (i, nm->interfaces,
+  ({
+    if (fn (i, ctx))
+      break;
+  }));
+  /* *INDENT-ON* */
+}
+
+int
+nat64_alloc_out_addr_and_port (u32 fib_index, snat_protocol_t proto,
+			       ip4_address_t * addr, u16 * port)
+{
+  nat64_main_t *nm = &nat64_main;
+  snat_main_t *sm = &snat_main;
+  int i;
+  snat_address_t *a, *ga = 0;
+  u32 portnum;
+
+  for (i = 0; i < vec_len (nm->addr_pool); i++)
+    {
+      a = nm->addr_pool + i;
+      switch (proto)
+	{
+#define _(N, j, n, s) \
+        case SNAT_PROTOCOL_##N: \
+          if (a->busy_##n##_ports < (65535-1024)) \
+            { \
+              if (a->fib_index == fib_index) \
+                { \
+                  while (1) \
+                    { \
+                      portnum = random_u32 (&sm->random_seed); \
+                      portnum &= 0xFFFF; \
+                      if (portnum < 1024) \
+                        continue; \
+                      if (clib_bitmap_get_no_check (a->busy_##n##_port_bitmap, \
+                                                    portnum)) \
+                        continue; \
+                      clib_bitmap_set_no_check (a->busy_##n##_port_bitmap, \
+                                                portnum, 1); \
+                      a->busy_##n##_ports++; \
+                      *port = portnum; \
+                      addr->as_u32 = a->addr.as_u32; \
+                      return 0; \
+                    } \
+                 } \
+               else if (a->fib_index == 0) \
+                 ga = a; \
+            } \
+          break;
+	  foreach_snat_protocol
+#undef _
+	default:
+	  clib_warning ("unknown protocol");
+	  return 1;
+	}
+    }
+
+  if (ga)
+    {
+      switch (proto)
+	{
+#define _(N, j, n, s) \
+        case SNAT_PROTOCOL_##N: \
+          while (1) \
+            { \
+              portnum = random_u32 (&sm->random_seed); \
+              portnum &= 0xFFFF; \
+              if (portnum < 1024) \
+                continue; \
+              if (clib_bitmap_get_no_check (a->busy_##n##_port_bitmap, \
+                                            portnum)) \
+                continue; \
+              clib_bitmap_set_no_check (a->busy_##n##_port_bitmap, \
+                                        portnum, 1); \
+              a->busy_##n##_ports++; \
+              *port = portnum; \
+              addr->as_u32 = a->addr.as_u32; \
+              return 0; \
+            }
+	  break;
+	  foreach_snat_protocol
+#undef _
+	default:
+	  clib_warning ("unknown protocol");
+	  return 1;
+	}
+    }
+
+  /* Totally out of translations to use... */
+  //TODO: IPFix
+  return 1;
+}
+
+void
+nat64_free_out_addr_and_port (ip4_address_t * addr, u16 port,
+			      snat_protocol_t proto)
+{
+  nat64_main_t *nm = &nat64_main;
+  int i;
+  snat_address_t *a;
+
+  for (i = 0; i < vec_len (nm->addr_pool); i++)
+    {
+      a = nm->addr_pool + i;
+      if (addr->as_u32 != a->addr.as_u32)
+	continue;
+      switch (proto)
+	{
+#define _(N, j, n, s) \
+        case SNAT_PROTOCOL_##N: \
+          ASSERT (clib_bitmap_get_no_check (a->busy_##n##_port_bitmap, \
+                  port) == 1); \
+          clib_bitmap_set_no_check (a->busy_##n##_port_bitmap, port, 0); \
+          a->busy_##n##_ports--; \
+          break;
+	  foreach_snat_protocol
+#undef _
+	default:
+	  clib_warning ("unknown protocol");
+	  return;
+	}
+      break;
+    }
+}
+
+int
+nat64_add_del_static_bib_entry (ip6_address_t * in_addr,
+				ip4_address_t * out_addr, u16 in_port,
+				u16 out_port, u8 proto, u32 vrf_id, u8 is_add)
+{
+  nat64_main_t *nm = &nat64_main;
+  nat64_db_bib_entry_t *bibe;
+  u32 fib_index =
+    fib_table_find_or_create_and_lock (FIB_PROTOCOL_IP6, vrf_id);
+  snat_protocol_t p = ip_proto_to_snat_proto (proto);
+  ip46_address_t addr;
+  int i;
+  snat_address_t *a;
+
+  addr.as_u64[0] = in_addr->as_u64[0];
+  addr.as_u64[1] = in_addr->as_u64[1];
+  bibe =
+    nat64_db_bib_entry_find (&nm->db, &addr, clib_host_to_net_u16 (in_port),
+			     proto, fib_index, 1);
+
+  if (is_add)
+    {
+      if (bibe)
+	return VNET_API_ERROR_VALUE_EXIST;
+
+      for (i = 0; i < vec_len (nm->addr_pool); i++)
+	{
+	  a = nm->addr_pool + i;
+	  if (out_addr->as_u32 != a->addr.as_u32)
+	    continue;
+	  switch (p)
+	    {
+#define _(N, j, n, s) \
+            case SNAT_PROTOCOL_##N: \
+              if (clib_bitmap_get_no_check (a->busy_##n##_port_bitmap, \
+                                            out_port)) \
+                return VNET_API_ERROR_INVALID_VALUE; \
+              clib_bitmap_set_no_check (a->busy_##n##_port_bitmap, \
+                                        out_port, 1); \
+              if (out_port > 1024) \
+                a->busy_##n##_ports++; \
+              break;
+	      foreach_snat_protocol
+#undef _
+	    default:
+	      memset (&addr, 0, sizeof (addr));
+	      addr.ip4.as_u32 = out_addr->as_u32;
+	      if (nat64_db_bib_entry_find
+		  (&nm->db, &addr, 0, proto, fib_index, 0))
+		return VNET_API_ERROR_INVALID_VALUE;
+	    }
+	  break;
+	}
+      bibe =
+	nat64_db_bib_entry_create (&nm->db, in_addr, out_addr,
+				   clib_host_to_net_u16 (in_port),
+				   clib_host_to_net_u16 (out_port), fib_index,
+				   proto, 1);
+      if (!bibe)
+	return VNET_API_ERROR_UNSPECIFIED;
+    }
+  else
+    {
+      if (!bibe)
+	return VNET_API_ERROR_NO_SUCH_ENTRY;
+
+      nat64_free_out_addr_and_port (out_addr, out_port, p);
+      nat64_db_bib_entry_free (&nm->db, bibe);
+    }
+
+  return 0;
+}
+
+int
+nat64_set_udp_timeout (u32 timeout)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  if (timeout == 0)
+    nm->udp_timeout = SNAT_UDP_TIMEOUT;
+  else if (timeout < SNAT_UDP_TIMEOUT_MIN)
+    return VNET_API_ERROR_INVALID_VALUE;
+  else
+    nm->udp_timeout = timeout;
+
+  return 0;
+}
+
+u32
+nat64_get_udp_timeout (void)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  return nm->udp_timeout;
+}
+
+int
+nat64_set_icmp_timeout (u32 timeout)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  if (timeout == 0)
+    nm->icmp_timeout = SNAT_ICMP_TIMEOUT;
+  else
+    nm->icmp_timeout = timeout;
+
+  return 0;
+}
+
+u32
+nat64_get_icmp_timeout (void)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  return nm->icmp_timeout;
+}
+
+int
+nat64_set_tcp_timeouts (u32 trans, u32 est, u32 incoming_syn)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  if (trans == 0)
+    nm->tcp_trans_timeout = SNAT_TCP_TRANSITORY_TIMEOUT;
+  else
+    nm->tcp_trans_timeout = trans;
+
+  if (est == 0)
+    nm->tcp_est_timeout = SNAT_TCP_ESTABLISHED_TIMEOUT;
+  else
+    nm->tcp_est_timeout = est;
+
+  if (incoming_syn == 0)
+    nm->tcp_incoming_syn_timeout = SNAT_TCP_INCOMING_SYN;
+  else
+    nm->tcp_incoming_syn_timeout = incoming_syn;
+
+  return 0;
+}
+
+u32
+nat64_get_tcp_trans_timeout (void)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  return nm->tcp_trans_timeout;
+}
+
+u32
+nat64_get_tcp_est_timeout (void)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  return nm->tcp_est_timeout;
+}
+
+u32
+nat64_get_tcp_incoming_syn_timeout (void)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  return nm->tcp_incoming_syn_timeout;
+}
+
+void
+nat64_session_reset_timeout (nat64_db_st_entry_t * ste, vlib_main_t * vm)
+{
+  nat64_main_t *nm = &nat64_main;
+  u32 now = (u32) vlib_time_now (vm);
+
+  switch (ip_proto_to_snat_proto (ste->proto))
+    {
+    case SNAT_PROTOCOL_ICMP:
+      ste->expire = now + nm->icmp_timeout;
+      return;
+    case SNAT_PROTOCOL_TCP:
+      {
+	switch (ste->tcp_state)
+	  {
+	  case NAT64_TCP_STATE_V4_INIT:
+	  case NAT64_TCP_STATE_V6_INIT:
+	  case NAT64_TCP_STATE_V4_FIN_RCV:
+	  case NAT64_TCP_STATE_V6_FIN_RCV:
+	  case NAT64_TCP_STATE_V6_FIN_V4_FIN_RCV:
+	  case NAT64_TCP_STATE_TRANS:
+	    ste->expire = now + nm->tcp_trans_timeout;
+	    return;
+	  case NAT64_TCP_STATE_ESTABLISHED:
+	    ste->expire = now + nm->tcp_est_timeout;
+	    return;
+	  default:
+	    return;
+	  }
+      }
+    case SNAT_PROTOCOL_UDP:
+      ste->expire = now + nm->udp_timeout;
+      return;
+    default:
+      ste->expire = now + nm->udp_timeout;
+      return;
+    }
+}
+
+void
+nat64_tcp_session_set_state (nat64_db_st_entry_t * ste, tcp_header_t * tcp,
+			     u8 is_ip6)
+{
+  switch (ste->tcp_state)
+    {
+    case NAT64_TCP_STATE_CLOSED:
+      {
+	if (tcp->flags & TCP_FLAG_SYN)
+	  {
+	    if (is_ip6)
+	      ste->tcp_state = NAT64_TCP_STATE_V6_INIT;
+	    else
+	      ste->tcp_state = NAT64_TCP_STATE_V4_INIT;
+	  }
+	return;
+      }
+    case NAT64_TCP_STATE_V4_INIT:
+      {
+	if (is_ip6 && (tcp->flags & TCP_FLAG_SYN))
+	  ste->tcp_state = NAT64_TCP_STATE_ESTABLISHED;
+	return;
+      }
+    case NAT64_TCP_STATE_V6_INIT:
+      {
+	if (!is_ip6 && (tcp->flags & TCP_FLAG_SYN))
+	  ste->tcp_state = NAT64_TCP_STATE_ESTABLISHED;
+	return;
+      }
+    case NAT64_TCP_STATE_ESTABLISHED:
+      {
+	if (tcp->flags & TCP_FLAG_FIN)
+	  {
+	    if (is_ip6)
+	      ste->tcp_state = NAT64_TCP_STATE_V6_FIN_RCV;
+	    else
+	      ste->tcp_state = NAT64_TCP_STATE_V4_FIN_RCV;
+	  }
+	else if (tcp->flags & TCP_FLAG_RST)
+	  {
+	    ste->tcp_state = NAT64_TCP_STATE_TRANS;
+	  }
+	return;
+      }
+    case NAT64_TCP_STATE_V4_FIN_RCV:
+      {
+	if (is_ip6 && (tcp->flags & TCP_FLAG_FIN))
+	  ste->tcp_state = NAT64_TCP_STATE_V6_FIN_V4_FIN_RCV;
+	return;
+      }
+    case NAT64_TCP_STATE_V6_FIN_RCV:
+      {
+	if (!is_ip6 && (tcp->flags & TCP_FLAG_FIN))
+	  ste->tcp_state = NAT64_TCP_STATE_V6_FIN_V4_FIN_RCV;
+	return;
+      }
+    case NAT64_TCP_STATE_TRANS:
+      {
+	if (!(tcp->flags & TCP_FLAG_RST))
+	  ste->tcp_state = NAT64_TCP_STATE_ESTABLISHED;
+	return;
+      }
+    default:
+      return;
+    }
+}
+
+int
+nat64_add_del_prefix (ip6_address_t * prefix, u8 plen, u32 vrf_id, u8 is_add)
+{
+  nat64_main_t *nm = &nat64_main;
+  nat64_prefix_t *p = 0;
+  int i;
+
+  /* Verify prefix length */
+  if (plen != 32 && plen != 40 && plen != 48 && plen != 56 && plen != 64
+      && plen != 96)
+    return VNET_API_ERROR_INVALID_VALUE;
+
+  /* Check if tenant already have prefix */
+  for (i = 0; i < vec_len (nm->pref64); i++)
+    {
+      if (nm->pref64[i].vrf_id == vrf_id)
+	{
+	  p = nm->pref64 + i;
+	  break;
+	}
+    }
+
+  if (is_add)
+    {
+      if (!p)
+	{
+	  vec_add2 (nm->pref64, p, 1);
+	  p->fib_index =
+	    fib_table_find_or_create_and_lock (FIB_PROTOCOL_IP6, vrf_id);
+	  p->vrf_id = vrf_id;
+	}
+
+      p->prefix.as_u64[0] = prefix->as_u64[0];
+      p->prefix.as_u64[1] = prefix->as_u64[1];
+      p->plen = plen;
+    }
+  else
+    {
+      if (!p)
+	return VNET_API_ERROR_NO_SUCH_ENTRY;
+
+      vec_del1 (nm->pref64, i);
+    }
+
+  return 0;
+}
+
+void
+nat64_prefix_walk (nat64_prefix_walk_fn_t fn, void *ctx)
+{
+  nat64_main_t *nm = &nat64_main;
+  nat64_prefix_t *p = 0;
+
+  /* *INDENT-OFF* */
+  vec_foreach (p, nm->pref64)
+    {
+      if (fn (p, ctx))
+        break;
+    };
+  /* *INDENT-ON* */
+}
+
+void
+nat64_compose_ip6 (ip6_address_t * ip6, ip4_address_t * ip4, u32 fib_index)
+{
+  nat64_main_t *nm = &nat64_main;
+  nat64_prefix_t *p, *gp = 0, *prefix = 0;
+
+  /* *INDENT-OFF* */
+  vec_foreach (p, nm->pref64)
+    {
+      if (p->fib_index == fib_index)
+        {
+          prefix = p;
+          break;
+        }
+
+      if (p->fib_index == 0)
+        gp = p;
+    };
+  /* *INDENT-ON* */
+
+  if (!prefix)
+    prefix = gp;
+
+  if (prefix)
+    {
+      memset (ip6, 0, 16);
+      memcpy (ip6, &p->prefix, p->plen);
+      switch (p->plen)
+	{
+	case 32:
+	  ip6->as_u32[1] = ip4->as_u32;
+	  break;
+	case 40:
+	  ip6->as_u8[5] = ip4->as_u8[0];
+	  ip6->as_u8[6] = ip4->as_u8[1];
+	  ip6->as_u8[7] = ip4->as_u8[2];
+	  ip6->as_u8[9] = ip4->as_u8[3];
+	  break;
+	case 48:
+	  ip6->as_u8[6] = ip4->as_u8[0];
+	  ip6->as_u8[7] = ip4->as_u8[1];
+	  ip6->as_u8[9] = ip4->as_u8[2];
+	  ip6->as_u8[10] = ip4->as_u8[3];
+	  break;
+	case 56:
+	  ip6->as_u8[7] = ip4->as_u8[0];
+	  ip6->as_u8[9] = ip4->as_u8[1];
+	  ip6->as_u8[10] = ip4->as_u8[2];
+	  ip6->as_u8[11] = ip4->as_u8[3];
+	  break;
+	case 64:
+	  ip6->as_u8[9] = ip4->as_u8[0];
+	  ip6->as_u8[10] = ip4->as_u8[1];
+	  ip6->as_u8[11] = ip4->as_u8[2];
+	  ip6->as_u8[12] = ip4->as_u8[3];
+	  break;
+	case 96:
+	  ip6->as_u32[3] = ip4->as_u32;
+	  break;
+	default:
+	  clib_warning ("invalid prefix length");
+	  break;
+	}
+    }
+  else
+    {
+      memcpy (ip6, well_known_prefix, 16);
+      ip6->as_u32[3] = ip4->as_u32;
+    }
+}
+
+void
+nat64_extract_ip4 (ip6_address_t * ip6, ip4_address_t * ip4, u32 fib_index)
+{
+  nat64_main_t *nm = &nat64_main;
+  nat64_prefix_t *p, *gp = 0;
+  u8 plen = 0;
+
+  /* *INDENT-OFF* */
+  vec_foreach (p, nm->pref64)
+    {
+      if (p->fib_index == fib_index)
+        {
+          plen = p->plen;
+          break;
+        }
+
+      if (p->vrf_id == 0)
+        gp = p;
+    };
+  /* *INDENT-ON* */
+
+  if (!plen)
+    {
+      if (gp)
+	plen = gp->plen;
+      else
+	plen = 96;
+    }
+
+  switch (plen)
+    {
+    case 32:
+      ip4->as_u32 = ip6->as_u32[1];
+      break;
+    case 40:
+      ip4->as_u8[0] = ip6->as_u8[5];
+      ip4->as_u8[1] = ip6->as_u8[6];
+      ip4->as_u8[2] = ip6->as_u8[7];
+      ip4->as_u8[3] = ip6->as_u8[9];
+      break;
+    case 48:
+      ip4->as_u8[0] = ip6->as_u8[6];
+      ip4->as_u8[1] = ip6->as_u8[7];
+      ip4->as_u8[2] = ip6->as_u8[9];
+      ip4->as_u8[3] = ip6->as_u8[10];
+      break;
+    case 56:
+      ip4->as_u8[0] = ip6->as_u8[7];
+      ip4->as_u8[1] = ip6->as_u8[9];
+      ip4->as_u8[2] = ip6->as_u8[10];
+      ip4->as_u8[3] = ip6->as_u8[11];
+      break;
+    case 64:
+      ip4->as_u8[0] = ip6->as_u8[9];
+      ip4->as_u8[1] = ip6->as_u8[10];
+      ip4->as_u8[2] = ip6->as_u8[11];
+      ip4->as_u8[3] = ip6->as_u8[12];
+      break;
+    case 96:
+      ip4->as_u32 = ip6->as_u32[3];
+      break;
+    default:
+      clib_warning ("invalid prefix length");
+      break;
+    }
+}
+
+/**
+ * @brief The 'nat64-expire-walk' process's main loop.
+ *
+ * Check expire time for NAT64 sessions.
+ */
+static uword
+nat64_expire_walk_fn (vlib_main_t * vm, vlib_node_runtime_t * rt,
+		      vlib_frame_t * f)
+{
+  nat64_main_t *nm = &nat64_main;
+
+  while (!nm->is_disabled)
+    {
+      vlib_process_wait_for_event_or_clock (vm, 10.0);
+      vlib_process_get_events (vm, NULL);
+      u32 now = (u32) vlib_time_now (vm);
+
+      nad64_db_st_free_expired (&nm->db, now);
+    }
+
+  return 0;
+}
+
+static vlib_node_registration_t nat64_expire_walk_node;
+
+/* *INDENT-OFF* */
+VLIB_REGISTER_NODE (nat64_expire_walk_node, static) = {
+    .function = nat64_expire_walk_fn,
+    .type = VLIB_NODE_TYPE_PROCESS,
+    .name = "nat64-expire-walk",
+};
+/* *INDENT-ON* */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */