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

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

1 files changed, 2294 insertions, 0 deletions

diff --git a/src/plugins/nat/out2in.c b/src/plugins/nat/out2in.c
new file mode 100644
index 00000000000..679500668c5
--- /dev/null
+++ b/src/plugins/nat/out2in.c
@@ -0,0 +1,2294 @@
+/*
+ * Copyright (c) 2016 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.
+ */
+
+#include <vlib/vlib.h>
+#include <vnet/vnet.h>
+#include <vnet/pg/pg.h>
+#include <vnet/handoff.h>
+
+#include <vnet/ip/ip.h>
+#include <vnet/udp/udp.h>
+#include <vnet/ethernet/ethernet.h>
+#include <vnet/fib/ip4_fib.h>
+#include <nat/nat.h>
+#include <nat/nat_ipfix_logging.h>
+#include <nat/nat_det.h>
+
+#include <vppinfra/hash.h>
+#include <vppinfra/error.h>
+#include <vppinfra/elog.h>
+
+typedef struct {
+  u32 sw_if_index;
+  u32 next_index;
+  u32 session_index;
+} snat_out2in_trace_t;
+
+typedef struct {
+  u32 next_worker_index;
+  u8 do_handoff;
+} snat_out2in_worker_handoff_trace_t;
+
+/* packet trace format function */
+static u8 * format_snat_out2in_trace (u8 * s, va_list * args)
+{
+  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
+  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
+  snat_out2in_trace_t * t = va_arg (*args, snat_out2in_trace_t *);
+
+  s = format (s, "NAT44_OUT2IN: sw_if_index %d, next index %d, session index %d",
+              t->sw_if_index, t->next_index, t->session_index);
+  return s;
+}
+
+static u8 * format_snat_out2in_fast_trace (u8 * s, va_list * args)
+{
+  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
+  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
+  snat_out2in_trace_t * t = va_arg (*args, snat_out2in_trace_t *);
+
+  s = format (s, "NAT44_OUT2IN_FAST: sw_if_index %d, next index %d",
+              t->sw_if_index, t->next_index);
+  return s;
+}
+
+static u8 * format_snat_out2in_worker_handoff_trace (u8 * s, va_list * args)
+{
+  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
+  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
+  snat_out2in_worker_handoff_trace_t * t =
+    va_arg (*args, snat_out2in_worker_handoff_trace_t *);
+  char * m;
+
+  m = t->do_handoff ? "next worker" : "same worker";
+  s = format (s, "NAT44_OUT2IN_WORKER_HANDOFF: %s %d", m, t->next_worker_index);
+
+  return s;
+}
+
+vlib_node_registration_t snat_out2in_node;
+vlib_node_registration_t snat_out2in_fast_node;
+vlib_node_registration_t snat_out2in_worker_handoff_node;
+vlib_node_registration_t snat_det_out2in_node;
+
+#define foreach_snat_out2in_error                       \
+_(UNSUPPORTED_PROTOCOL, "Unsupported protocol")         \
+_(OUT2IN_PACKETS, "Good out2in packets processed")      \
+_(BAD_ICMP_TYPE, "unsupported ICMP type")               \
+_(NO_TRANSLATION, "No translation")
+
+typedef enum {
+#define _(sym,str) SNAT_OUT2IN_ERROR_##sym,
+  foreach_snat_out2in_error
+#undef _
+  SNAT_OUT2IN_N_ERROR,
+} snat_out2in_error_t;
+
+static char * snat_out2in_error_strings[] = {
+#define _(sym,string) string,
+  foreach_snat_out2in_error
+#undef _
+};
+
+typedef enum {
+  SNAT_OUT2IN_NEXT_DROP,
+  SNAT_OUT2IN_NEXT_LOOKUP,
+  SNAT_OUT2IN_NEXT_ICMP_ERROR,
+  SNAT_OUT2IN_N_NEXT,
+} snat_out2in_next_t;
+
+/**
+ * @brief Create session for static mapping.
+ *
+ * Create NAT session initiated by host from external network with static
+ * mapping.
+ *
+ * @param sm     NAT main.
+ * @param b0     Vlib buffer.
+ * @param in2out In2out NAT44 session key.
+ * @param out2in Out2in NAT44 session key.
+ * @param node   Vlib node.
+ *
+ * @returns SNAT session if successfully created otherwise 0.
+ */
+static inline snat_session_t *
+create_session_for_static_mapping (snat_main_t *sm,
+                                   vlib_buffer_t *b0,
+                                   snat_session_key_t in2out,
+                                   snat_session_key_t out2in,
+                                   vlib_node_runtime_t * node,
+                                   u32 thread_index)
+{
+  snat_user_t *u;
+  snat_user_key_t user_key;
+  snat_session_t *s;
+  clib_bihash_kv_8_8_t kv0, value0;
+  dlist_elt_t * per_user_translation_list_elt;
+  dlist_elt_t * per_user_list_head_elt;
+  ip4_header_t *ip0;
+
+  ip0 = vlib_buffer_get_current (b0);
+
+  user_key.addr = in2out.addr;
+  user_key.fib_index = in2out.fib_index;
+  kv0.key = user_key.as_u64;
+
+  /* Ever heard of the "user" = inside ip4 address before? */
+  if (clib_bihash_search_8_8 (&sm->user_hash, &kv0, &value0))
+    {
+      /* no, make a new one */
+      pool_get (sm->per_thread_data[thread_index].users, u);
+      memset (u, 0, sizeof (*u));
+      u->addr = in2out.addr;
+      u->fib_index = in2out.fib_index;
+
+      pool_get (sm->per_thread_data[thread_index].list_pool,
+                per_user_list_head_elt);
+
+      u->sessions_per_user_list_head_index = per_user_list_head_elt -
+        sm->per_thread_data[thread_index].list_pool;
+
+      clib_dlist_init (sm->per_thread_data[thread_index].list_pool,
+                       u->sessions_per_user_list_head_index);
+
+      kv0.value = u - sm->per_thread_data[thread_index].users;
+
+      /* add user */
+      clib_bihash_add_del_8_8 (&sm->user_hash, &kv0, 1 /* is_add */);
+
+      /* add non-traslated packets worker lookup */
+      kv0.value = thread_index;
+      clib_bihash_add_del_8_8 (&sm->worker_by_in, &kv0, 1);
+    }
+  else
+    {
+      u = pool_elt_at_index (sm->per_thread_data[thread_index].users,
+                             value0.value);
+    }
+
+  pool_get (sm->per_thread_data[thread_index].sessions, s);
+  memset (s, 0, sizeof (*s));
+
+  s->outside_address_index = ~0;
+  s->flags |= SNAT_SESSION_FLAG_STATIC_MAPPING;
+  s->ext_host_addr.as_u32 = ip0->dst_address.as_u32;
+  u->nstaticsessions++;
+
+  /* Create list elts */
+  pool_get (sm->per_thread_data[thread_index].list_pool,
+            per_user_translation_list_elt);
+  clib_dlist_init (sm->per_thread_data[thread_index].list_pool,
+                   per_user_translation_list_elt -
+                   sm->per_thread_data[thread_index].list_pool);
+
+  per_user_translation_list_elt->value =
+    s - sm->per_thread_data[thread_index].sessions;
+  s->per_user_index =
+    per_user_translation_list_elt - sm->per_thread_data[thread_index].list_pool;
+  s->per_user_list_head_index = u->sessions_per_user_list_head_index;
+
+  clib_dlist_addtail (sm->per_thread_data[thread_index].list_pool,
+                      s->per_user_list_head_index,
+                      per_user_translation_list_elt -
+                      sm->per_thread_data[thread_index].list_pool);
+
+  s->in2out = in2out;
+  s->out2in = out2in;
+  s->in2out.protocol = out2in.protocol;
+
+  /* Add to translation hashes */
+  kv0.key = s->in2out.as_u64;
+  kv0.value = s - sm->per_thread_data[thread_index].sessions;
+  if (clib_bihash_add_del_8_8 (&sm->in2out, &kv0, 1 /* is_add */))
+      clib_warning ("in2out key add failed");
+
+  kv0.key = s->out2in.as_u64;
+  kv0.value = s - sm->per_thread_data[thread_index].sessions;
+
+  if (clib_bihash_add_del_8_8 (&sm->out2in, &kv0, 1 /* is_add */))
+      clib_warning ("out2in key add failed");
+
+  /* log NAT event */
+  snat_ipfix_logging_nat44_ses_create(s->in2out.addr.as_u32,
+                                      s->out2in.addr.as_u32,
+                                      s->in2out.protocol,
+                                      s->in2out.port,
+                                      s->out2in.port,
+                                      s->in2out.fib_index);
+   return s;
+}
+
+static_always_inline
+snat_out2in_error_t icmp_get_key(ip4_header_t *ip0,
+                                 snat_session_key_t *p_key0)
+{
+  icmp46_header_t *icmp0;
+  snat_session_key_t key0;
+  icmp_echo_header_t *echo0, *inner_echo0 = 0;
+  ip4_header_t *inner_ip0;
+  void *l4_header = 0;
+  icmp46_header_t *inner_icmp0;
+
+  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
+  echo0 = (icmp_echo_header_t *)(icmp0+1);
+
+  if (!icmp_is_error_message (icmp0))
+    {
+      key0.protocol = SNAT_PROTOCOL_ICMP;
+      key0.addr = ip0->dst_address;
+      key0.port = echo0->identifier;
+    }
+  else
+    {
+      inner_ip0 = (ip4_header_t *)(echo0+1);
+      l4_header = ip4_next_header (inner_ip0);
+      key0.protocol = ip_proto_to_snat_proto (inner_ip0->protocol);
+      key0.addr = inner_ip0->src_address;
+      switch (key0.protocol)
+        {
+        case SNAT_PROTOCOL_ICMP:
+          inner_icmp0 = (icmp46_header_t*)l4_header;
+          inner_echo0 = (icmp_echo_header_t *)(inner_icmp0+1);
+          key0.port = inner_echo0->identifier;
+          break;
+        case SNAT_PROTOCOL_UDP:
+        case SNAT_PROTOCOL_TCP:
+          key0.port = ((tcp_udp_header_t*)l4_header)->src_port;
+          break;
+        default:
+          return SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL;
+        }
+    }
+  *p_key0 = key0;
+  return -1; /* success */
+}
+
+/**
+ * Get address and port values to be used for ICMP packet translation
+ * and create session if needed
+ *
+ * @param[in,out] sm             NAT main
+ * @param[in,out] node           NAT node runtime
+ * @param[in] thread_index       thread index
+ * @param[in,out] b0             buffer containing packet to be translated
+ * @param[out] p_proto           protocol used for matching
+ * @param[out] p_value           address and port after NAT translation
+ * @param[out] p_dont_translate  if packet should not be translated
+ * @param d                      optional parameter
+ * @param e                      optional parameter
+ */
+u32 icmp_match_out2in_slow(snat_main_t *sm, vlib_node_runtime_t *node,
+                           u32 thread_index, vlib_buffer_t *b0, u8 *p_proto,
+                           snat_session_key_t *p_value,
+                           u8 *p_dont_translate, void *d, void *e)
+{
+  ip4_header_t *ip0;
+  icmp46_header_t *icmp0;
+  u32 sw_if_index0;
+  u32 rx_fib_index0;
+  snat_session_key_t key0;
+  snat_session_key_t sm0;
+  snat_session_t *s0 = 0;
+  u8 dont_translate = 0;
+  clib_bihash_kv_8_8_t kv0, value0;
+  u8 is_addr_only;
+  u32 next0 = ~0;
+  int err;
+
+  ip0 = vlib_buffer_get_current (b0);
+  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
+  sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+  rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index (sw_if_index0);
+
+  key0.protocol = 0;
+
+  err = icmp_get_key (ip0, &key0);
+  if (err != -1)
+    {
+      b0->error = node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out;
+    }
+  key0.fib_index = rx_fib_index0;
+
+  kv0.key = key0.as_u64;
+
+  if (clib_bihash_search_8_8 (&sm->out2in, &kv0, &value0))
+    {
+      /* Try to match static mapping by external address and port,
+         destination address and port in packet */
+      if (snat_static_mapping_match(sm, key0, &sm0, 1, &is_addr_only))
+        {
+          /* Don't NAT packet aimed at the intfc address */
+          if (PREDICT_FALSE(is_interface_addr(sm, node, sw_if_index0,
+                                              ip0->dst_address.as_u32)))
+            {
+              dont_translate = 1;
+              goto out;
+            }
+          b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+          next0 = SNAT_OUT2IN_NEXT_DROP;
+          goto out;
+        }
+
+      if (PREDICT_FALSE(icmp0->type != ICMP4_echo_reply &&
+                        (icmp0->type != ICMP4_echo_request || !is_addr_only)))
+        {
+          b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
+          next0 = SNAT_OUT2IN_NEXT_DROP;
+          goto out;
+        }
+
+      /* Create session initiated by host from external network */
+      s0 = create_session_for_static_mapping(sm, b0, sm0, key0,
+                                             node, thread_index);
+
+      if (!s0)
+        {
+          next0 = SNAT_OUT2IN_NEXT_DROP;
+          goto out;
+        }
+    }
+  else
+    {
+      if (PREDICT_FALSE(icmp0->type != ICMP4_echo_reply &&
+                        icmp0->type != ICMP4_echo_request &&
+                        !icmp_is_error_message (icmp0)))
+        {
+          b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
+          next0 = SNAT_OUT2IN_NEXT_DROP;
+          goto out;
+        }
+
+      s0 = pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
+                              value0.value);
+    }
+
+out:
+  *p_proto = key0.protocol;
+  if (s0)
+    *p_value = s0->in2out;
+  *p_dont_translate = dont_translate;
+  if (d)
+    *(snat_session_t**)d = s0;
+  return next0;
+}
+
+/**
+ * Get address and port values to be used for ICMP packet translation
+ *
+ * @param[in] sm                 NAT main
+ * @param[in,out] node           NAT node runtime
+ * @param[in] thread_index       thread index
+ * @param[in,out] b0             buffer containing packet to be translated
+ * @param[out] p_proto           protocol used for matching
+ * @param[out] p_value           address and port after NAT translation
+ * @param[out] p_dont_translate  if packet should not be translated
+ * @param d                      optional parameter
+ * @param e                      optional parameter
+ */
+u32 icmp_match_out2in_fast(snat_main_t *sm, vlib_node_runtime_t *node,
+                           u32 thread_index, vlib_buffer_t *b0, u8 *p_proto,
+                           snat_session_key_t *p_value,
+                           u8 *p_dont_translate, void *d, void *e)
+{
+  ip4_header_t *ip0;
+  icmp46_header_t *icmp0;
+  u32 sw_if_index0;
+  u32 rx_fib_index0;
+  snat_session_key_t key0;
+  snat_session_key_t sm0;
+  u8 dont_translate = 0;
+  u8 is_addr_only;
+  u32 next0 = ~0;
+  int err;
+
+  ip0 = vlib_buffer_get_current (b0);
+  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
+  sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+  rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index (sw_if_index0);
+
+  err = icmp_get_key (ip0, &key0);
+  if (err != -1)
+    {
+      b0->error = node->errors[err];
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out2;
+    }
+  key0.fib_index = rx_fib_index0;
+
+  if (snat_static_mapping_match(sm, key0, &sm0, 1, &is_addr_only))
+    {
+      /* Don't NAT packet aimed at the intfc address */
+      if (is_interface_addr(sm, node, sw_if_index0, ip0->dst_address.as_u32))
+        {
+          dont_translate = 1;
+          goto out;
+        }
+      b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out;
+    }
+
+  if (PREDICT_FALSE(icmp0->type != ICMP4_echo_reply &&
+                    (icmp0->type != ICMP4_echo_request || !is_addr_only) &&
+                    !icmp_is_error_message (icmp0)))
+    {
+      b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out;
+    }
+
+out:
+  *p_value = sm0;
+out2:
+  *p_proto = key0.protocol;
+  *p_dont_translate = dont_translate;
+  return next0;
+}
+
+static inline u32 icmp_out2in (snat_main_t *sm,
+                               vlib_buffer_t * b0,
+                               ip4_header_t * ip0,
+                               icmp46_header_t * icmp0,
+                               u32 sw_if_index0,
+                               u32 rx_fib_index0,
+                               vlib_node_runtime_t * node,
+                               u32 next0,
+                               u32 thread_index,
+                               void *d,
+                               void *e)
+{
+  snat_session_key_t sm0;
+  u8 protocol;
+  icmp_echo_header_t *echo0, *inner_echo0 = 0;
+  ip4_header_t *inner_ip0 = 0;
+  void *l4_header = 0;
+  icmp46_header_t *inner_icmp0;
+  u8 dont_translate;
+  u32 new_addr0, old_addr0;
+  u16 old_id0, new_id0;
+  ip_csum_t sum0;
+  u16 checksum0;
+  u32 next0_tmp;
+
+  echo0 = (icmp_echo_header_t *)(icmp0+1);
+
+  next0_tmp = sm->icmp_match_out2in_cb(sm, node, thread_index, b0,
+                                       &protocol, &sm0, &dont_translate, d, e);
+  if (next0_tmp != ~0)
+    next0 = next0_tmp;
+  if (next0 == SNAT_OUT2IN_NEXT_DROP || dont_translate)
+    goto out;
+
+  sum0 = ip_incremental_checksum (0, icmp0,
+                                  ntohs(ip0->length) - ip4_header_bytes (ip0));
+  checksum0 = ~ip_csum_fold (sum0);
+  if (checksum0 != 0 && checksum0 != 0xffff)
+    {
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out;
+    }
+
+  old_addr0 = ip0->dst_address.as_u32;
+  new_addr0 = ip0->dst_address.as_u32 = sm0.addr.as_u32;
+  vnet_buffer(b0)->sw_if_index[VLIB_TX] = sm0.fib_index;
+
+  sum0 = ip0->checksum;
+  sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+                         dst_address /* changed member */);
+  ip0->checksum = ip_csum_fold (sum0);
+
+  if (!icmp_is_error_message (icmp0))
+    {
+      new_id0 = sm0.port;
+      if (PREDICT_FALSE(new_id0 != echo0->identifier))
+        {
+          old_id0 = echo0->identifier;
+          new_id0 = sm0.port;
+          echo0->identifier = new_id0;
+
+          sum0 = icmp0->checksum;
+          sum0 = ip_csum_update (sum0, old_id0, new_id0, icmp_echo_header_t,
+                                 identifier /* changed member */);
+          icmp0->checksum = ip_csum_fold (sum0);
+        }
+    }
+  else
+    {
+      inner_ip0 = (ip4_header_t *)(echo0+1);
+      l4_header = ip4_next_header (inner_ip0);
+
+      if (!ip4_header_checksum_is_valid (inner_ip0))
+        {
+          next0 = SNAT_OUT2IN_NEXT_DROP;
+          goto out;
+        }
+
+      old_addr0 = inner_ip0->src_address.as_u32;
+      inner_ip0->src_address = sm0.addr;
+      new_addr0 = inner_ip0->src_address.as_u32;
+
+      sum0 = icmp0->checksum;
+      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+                             src_address /* changed member */);
+      icmp0->checksum = ip_csum_fold (sum0);
+
+      switch (protocol)
+        {
+        case SNAT_PROTOCOL_ICMP:
+          inner_icmp0 = (icmp46_header_t*)l4_header;
+          inner_echo0 = (icmp_echo_header_t *)(inner_icmp0+1);
+
+          old_id0 = inner_echo0->identifier;
+          new_id0 = sm0.port;
+          inner_echo0->identifier = new_id0;
+
+          sum0 = icmp0->checksum;
+          sum0 = ip_csum_update (sum0, old_id0, new_id0, icmp_echo_header_t,
+                                 identifier);
+          icmp0->checksum = ip_csum_fold (sum0);
+          break;
+        case SNAT_PROTOCOL_UDP:
+        case SNAT_PROTOCOL_TCP:
+          old_id0 = ((tcp_udp_header_t*)l4_header)->src_port;
+          new_id0 = sm0.port;
+          ((tcp_udp_header_t*)l4_header)->src_port = new_id0;
+
+          sum0 = icmp0->checksum;
+          sum0 = ip_csum_update (sum0, old_id0, new_id0, tcp_udp_header_t,
+                                 src_port);
+          icmp0->checksum = ip_csum_fold (sum0);
+          break;
+        default:
+          ASSERT(0);
+        }
+    }
+
+out:
+  return next0;
+}
+
+
+static inline u32 icmp_out2in_slow_path (snat_main_t *sm,
+                                         vlib_buffer_t * b0,
+                                         ip4_header_t * ip0,
+                                         icmp46_header_t * icmp0,
+                                         u32 sw_if_index0,
+                                         u32 rx_fib_index0,
+                                         vlib_node_runtime_t * node,
+                                         u32 next0, f64 now,
+                                         u32 thread_index,
+                                         snat_session_t ** p_s0)
+{
+  next0 = icmp_out2in(sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
+                      next0, thread_index, p_s0, 0);
+  snat_session_t * s0 = *p_s0;
+  if (PREDICT_TRUE(next0 != SNAT_OUT2IN_NEXT_DROP && s0))
+    {
+      /* Accounting */
+      s0->last_heard = now;
+      s0->total_pkts++;
+      s0->total_bytes += vlib_buffer_length_in_chain (sm->vlib_main, b0);
+      /* Per-user LRU list maintenance for dynamic translation */
+      if (!snat_is_session_static (s0))
+        {
+          clib_dlist_remove (sm->per_thread_data[thread_index].list_pool,
+                             s0->per_user_index);
+          clib_dlist_addtail (sm->per_thread_data[thread_index].list_pool,
+                              s0->per_user_list_head_index,
+                              s0->per_user_index);
+        }
+    }
+  return next0;
+}
+
+static void
+snat_out2in_unknown_proto (snat_main_t *sm,
+                           vlib_buffer_t * b,
+                           ip4_header_t * ip,
+                           u32 rx_fib_index,
+                           u32 thread_index,
+                           f64 now,
+                           vlib_main_t * vm)
+{
+  clib_bihash_kv_8_8_t kv, value;
+  clib_bihash_kv_16_8_t s_kv, s_value;
+  snat_static_mapping_t *m;
+  snat_session_key_t m_key;
+  u32 old_addr, new_addr;
+  ip_csum_t sum;
+  snat_unk_proto_ses_key_t key;
+  snat_session_t * s;
+  snat_main_per_thread_data_t *tsm = &sm->per_thread_data[thread_index];
+  snat_user_key_t u_key;
+  snat_user_t *u;
+  dlist_elt_t *head, *elt;
+
+  old_addr = ip->dst_address.as_u32;
+
+  key.l_addr = ip->dst_address;
+  key.r_addr = ip->src_address;
+  key.fib_index = rx_fib_index;
+  key.proto = ip->protocol;
+  key.rsvd[0] = key.rsvd[1] = key.rsvd[2] = 0;
+  s_kv.key[0] = key.as_u64[0];
+  s_kv.key[1] = key.as_u64[1];
+
+  if (!clib_bihash_search_16_8 (&sm->out2in_unk_proto, &s_kv, &s_value))
+    {
+      s = pool_elt_at_index (tsm->sessions, s_value.value);
+      new_addr = ip->dst_address.as_u32 = s->in2out.addr.as_u32;
+    }
+  else
+    {
+      m_key.addr = ip->dst_address;
+      m_key.port = 0;
+      m_key.protocol = 0;
+      m_key.fib_index = rx_fib_index;
+      kv.key = m_key.as_u64;
+      if (clib_bihash_search_8_8 (&sm->static_mapping_by_external, &kv, &value))
+        return;
+
+      m = pool_elt_at_index (sm->static_mappings, value.value);
+
+      new_addr = ip->dst_address.as_u32 = m->local_addr.as_u32;
+
+      u_key.addr = ip->src_address;
+      u_key.fib_index = m->fib_index;
+      kv.key = u_key.as_u64;
+
+      /* Ever heard of the "user" = src ip4 address before? */
+      if (clib_bihash_search_8_8 (&sm->user_hash, &kv, &value))
+        {
+          /* no, make a new one */
+          pool_get (tsm->users, u);
+          memset (u, 0, sizeof (*u));
+          u->addr = ip->src_address;
+          u->fib_index = rx_fib_index;
+
+          pool_get (tsm->list_pool, head);
+          u->sessions_per_user_list_head_index = head - tsm->list_pool;
+
+          clib_dlist_init (tsm->list_pool,
+                           u->sessions_per_user_list_head_index);
+
+          kv.value = u - tsm->users;
+
+          /* add user */
+          clib_bihash_add_del_8_8 (&sm->user_hash, &kv, 1);
+        }
+      else
+        {
+          u = pool_elt_at_index (tsm->users, value.value);
+        }
+
+      /* Create a new session */
+      pool_get (tsm->sessions, s);
+      memset (s, 0, sizeof (*s));
+
+      s->ext_host_addr.as_u32 = ip->src_address.as_u32;
+      s->flags |= SNAT_SESSION_FLAG_UNKNOWN_PROTO;
+      s->flags |= SNAT_SESSION_FLAG_STATIC_MAPPING;
+      s->outside_address_index = ~0;
+      s->out2in.addr.as_u32 = old_addr;
+      s->out2in.fib_index = rx_fib_index;
+      s->in2out.addr.as_u32 = new_addr;
+      s->in2out.fib_index = m->fib_index;
+      s->in2out.port = s->out2in.port = ip->protocol;
+      u->nstaticsessions++;
+
+      /* Create list elts */
+      pool_get (tsm->list_pool, elt);
+      clib_dlist_init (tsm->list_pool, elt - tsm->list_pool);
+      elt->value = s - tsm->sessions;
+      s->per_user_index = elt - tsm->list_pool;
+      s->per_user_list_head_index = u->sessions_per_user_list_head_index;
+      clib_dlist_addtail (tsm->list_pool, s->per_user_list_head_index,
+                          s->per_user_index);
+
+      /* Add to lookup tables */
+      s_kv.value = s - tsm->sessions;
+      if (clib_bihash_add_del_16_8 (&sm->out2in_unk_proto, &s_kv, 1))
+        clib_warning ("out2in key add failed");
+
+      key.l_addr = ip->dst_address;
+      key.fib_index = m->fib_index;
+      s_kv.key[0] = key.as_u64[0];
+      s_kv.key[1] = key.as_u64[1];
+      if (clib_bihash_add_del_16_8 (&sm->in2out_unk_proto, &s_kv, 1))
+        clib_warning ("in2out key add failed");
+   }
+
+  /* Update IP checksum */
+  sum = ip->checksum;
+  sum = ip_csum_update (sum, old_addr, new_addr, ip4_header_t, dst_address);
+  ip->checksum = ip_csum_fold (sum);
+
+  vnet_buffer(b)->sw_if_index[VLIB_TX] = s->in2out.fib_index;
+
+  /* Accounting */
+  s->last_heard = now;
+  s->total_pkts++;
+  s->total_bytes += vlib_buffer_length_in_chain (vm, b);
+  /* Per-user LRU list maintenance */
+  clib_dlist_remove (tsm->list_pool, s->per_user_index);
+  clib_dlist_addtail (tsm->list_pool, s->per_user_list_head_index,
+                      s->per_user_index);
+}
+
+static uword
+snat_out2in_node_fn (vlib_main_t * vm,
+		  vlib_node_runtime_t * node,
+		  vlib_frame_t * frame)
+{
+  u32 n_left_from, * from, * to_next;
+  snat_out2in_next_t next_index;
+  u32 pkts_processed = 0;
+  snat_main_t * sm = &snat_main;
+  f64 now = vlib_time_now (vm);
+  u32 thread_index = vlib_get_thread_index ();
+
+  from = vlib_frame_vector_args (frame);
+  n_left_from = frame->n_vectors;
+  next_index = node->cached_next_index;
+
+  while (n_left_from > 0)
+    {
+      u32 n_left_to_next;
+
+      vlib_get_next_frame (vm, node, next_index,
+			   to_next, n_left_to_next);
+
+      while (n_left_from >= 4 && n_left_to_next >= 2)
+	{
+          u32 bi0, bi1;
+	  vlib_buffer_t * b0, * b1;
+          u32 next0 = SNAT_OUT2IN_NEXT_LOOKUP;
+          u32 next1 = SNAT_OUT2IN_NEXT_LOOKUP;
+          u32 sw_if_index0, sw_if_index1;
+          ip4_header_t * ip0, *ip1;
+          ip_csum_t sum0, sum1;
+          u32 new_addr0, old_addr0;
+          u16 new_port0, old_port0;
+          u32 new_addr1, old_addr1;
+          u16 new_port1, old_port1;
+          udp_header_t * udp0, * udp1;
+          tcp_header_t * tcp0, * tcp1;
+          icmp46_header_t * icmp0, * icmp1;
+          snat_session_key_t key0, key1, sm0, sm1;
+          u32 rx_fib_index0, rx_fib_index1;
+          u32 proto0, proto1;
+          snat_session_t * s0 = 0, * s1 = 0;
+          clib_bihash_kv_8_8_t kv0, kv1, value0, value1;
+
+	  /* Prefetch next iteration. */
+	  {
+	    vlib_buffer_t * p2, * p3;
+
+	    p2 = vlib_get_buffer (vm, from[2]);
+	    p3 = vlib_get_buffer (vm, from[3]);
+
+	    vlib_prefetch_buffer_header (p2, LOAD);
+	    vlib_prefetch_buffer_header (p3, LOAD);
+
+	    CLIB_PREFETCH (p2->data, CLIB_CACHE_LINE_BYTES, STORE);
+	    CLIB_PREFETCH (p3->data, CLIB_CACHE_LINE_BYTES, STORE);
+	  }
+
+          /* speculatively enqueue b0 and b1 to the current next frame */
+	  to_next[0] = bi0 = from[0];
+	  to_next[1] = bi1 = from[1];
+	  from += 2;
+	  to_next += 2;
+	  n_left_from -= 2;
+	  n_left_to_next -= 2;
+
+	  b0 = vlib_get_buffer (vm, bi0);
+	  b1 = vlib_get_buffer (vm, bi1);
+
+          vnet_buffer (b0)->snat.flags = 0;
+          vnet_buffer (b1)->snat.flags = 0;
+
+          ip0 = vlib_buffer_get_current (b0);
+          udp0 = ip4_next_header (ip0);
+          tcp0 = (tcp_header_t *) udp0;
+          icmp0 = (icmp46_header_t *) udp0;
+
+          sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+	  rx_fib_index0 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index,
+                                   sw_if_index0);
+
+          if (PREDICT_FALSE(ip0->ttl == 1))
+            {
+              vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace0;
+            }
+
+          proto0 = ip_proto_to_snat_proto (ip0->protocol);
+
+          if (PREDICT_FALSE (proto0 == ~0))
+            {
+              snat_out2in_unknown_proto(sm, b0, ip0, rx_fib_index0,
+                                        thread_index, now, vm);
+              goto trace0;
+            }
+
+          if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
+            {
+              next0 = icmp_out2in_slow_path
+                (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
+                 next0, now, thread_index, &s0);
+              goto trace0;
+            }
+
+          key0.addr = ip0->dst_address;
+          key0.port = udp0->dst_port;
+          key0.protocol = proto0;
+          key0.fib_index = rx_fib_index0;
+
+          kv0.key = key0.as_u64;
+
+          if (clib_bihash_search_8_8 (&sm->out2in, &kv0, &value0))
+            {
+              /* Try to match static mapping by external address and port,
+                 destination address and port in packet */
+              if (snat_static_mapping_match(sm, key0, &sm0, 1, 0))
+                {
+                  b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+                  /*
+                   * Send DHCP packets to the ipv4 stack, or we won't
+                   * be able to use dhcp client on the outside interface
+                   */
+                  if (proto0 != SNAT_PROTOCOL_UDP
+                      || (udp0->dst_port
+                          != clib_host_to_net_u16(UDP_DST_PORT_dhcp_to_client)))
+                    next0 = SNAT_OUT2IN_NEXT_DROP;
+                  goto trace0;
+                }
+
+              /* Create session initiated by host from external network */
+              s0 = create_session_for_static_mapping(sm, b0, sm0, key0, node,
+                                                     thread_index);
+              if (!s0)
+                {
+                  b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+                  next0 = SNAT_OUT2IN_NEXT_DROP;
+                  goto trace0;
+                }
+            }
+          else
+            s0 = pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
+                                    value0.value);
+
+          old_addr0 = ip0->dst_address.as_u32;
+          ip0->dst_address = s0->in2out.addr;
+          new_addr0 = ip0->dst_address.as_u32;
+          vnet_buffer(b0)->sw_if_index[VLIB_TX] = s0->in2out.fib_index;
+
+          sum0 = ip0->checksum;
+          sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip0->checksum = ip_csum_fold (sum0);
+
+          if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+            {
+              old_port0 = tcp0->dst_port;
+              tcp0->dst_port = s0->in2out.port;
+              new_port0 = tcp0->dst_port;
+
+              sum0 = tcp0->checksum;
+              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                     ip4_header_t,
+                                     dst_address /* changed member */);
+
+              sum0 = ip_csum_update (sum0, old_port0, new_port0,
+                                     ip4_header_t /* cheat */,
+                                     length /* changed member */);
+              tcp0->checksum = ip_csum_fold(sum0);
+            }
+          else
+            {
+              old_port0 = udp0->dst_port;
+              udp0->dst_port = s0->in2out.port;
+              udp0->checksum = 0;
+            }
+
+          /* Accounting */
+          s0->last_heard = now;
+          s0->total_pkts++;
+          s0->total_bytes += vlib_buffer_length_in_chain (vm, b0);
+          /* Per-user LRU list maintenance for dynamic translation */
+          if (!snat_is_session_static (s0))
+            {
+              clib_dlist_remove (sm->per_thread_data[thread_index].list_pool,
+                                 s0->per_user_index);
+              clib_dlist_addtail (sm->per_thread_data[thread_index].list_pool,
+                                  s0->per_user_list_head_index,
+                                  s0->per_user_index);
+            }
+        trace0:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b0, sizeof (*t));
+              t->sw_if_index = sw_if_index0;
+              t->next_index = next0;
+              t->session_index = ~0;
+              if (s0)
+                t->session_index = s0 - sm->per_thread_data[thread_index].sessions;
+            }
+
+          pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;
+
+
+          ip1 = vlib_buffer_get_current (b1);
+          udp1 = ip4_next_header (ip1);
+          tcp1 = (tcp_header_t *) udp1;
+          icmp1 = (icmp46_header_t *) udp1;
+
+          sw_if_index1 = vnet_buffer(b1)->sw_if_index[VLIB_RX];
+	  rx_fib_index1 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index,
+                                   sw_if_index1);
+
+          if (PREDICT_FALSE(ip1->ttl == 1))
+            {
+              vnet_buffer (b1)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b1, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next1 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace1;
+            }
+
+          proto1 = ip_proto_to_snat_proto (ip1->protocol);
+
+          if (PREDICT_FALSE (proto1 == ~0))
+            {
+              snat_out2in_unknown_proto(sm, b1, ip1, rx_fib_index1,
+                                        thread_index, now, vm);
+              goto trace1;
+            }
+
+          if (PREDICT_FALSE (proto1 == SNAT_PROTOCOL_ICMP))
+            {
+              next1 = icmp_out2in_slow_path
+                (sm, b1, ip1, icmp1, sw_if_index1, rx_fib_index1, node,
+                 next1, now, thread_index, &s1);
+              goto trace1;
+            }
+
+          key1.addr = ip1->dst_address;
+          key1.port = udp1->dst_port;
+          key1.protocol = proto1;
+          key1.fib_index = rx_fib_index1;
+
+          kv1.key = key1.as_u64;
+
+          if (clib_bihash_search_8_8 (&sm->out2in, &kv1, &value1))
+            {
+              /* Try to match static mapping by external address and port,
+                 destination address and port in packet */
+              if (snat_static_mapping_match(sm, key1, &sm1, 1, 0))
+                {
+                  b1->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+                  /*
+                   * Send DHCP packets to the ipv4 stack, or we won't
+                   * be able to use dhcp client on the outside interface
+                   */
+                  if (proto1 != SNAT_PROTOCOL_UDP
+                      || (udp1->dst_port
+                          != clib_host_to_net_u16(UDP_DST_PORT_dhcp_to_client)))
+                    next1 = SNAT_OUT2IN_NEXT_DROP;
+                  goto trace1;
+                }
+
+              /* Create session initiated by host from external network */
+              s1 = create_session_for_static_mapping(sm, b1, sm1, key1, node,
+                                                     thread_index);
+              if (!s1)
+                {
+                  b1->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+                  next1 = SNAT_OUT2IN_NEXT_DROP;
+                  goto trace1;
+                }
+            }
+          else
+            s1 = pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
+                                    value1.value);
+
+          old_addr1 = ip1->dst_address.as_u32;
+          ip1->dst_address = s1->in2out.addr;
+          new_addr1 = ip1->dst_address.as_u32;
+          vnet_buffer(b1)->sw_if_index[VLIB_TX] = s1->in2out.fib_index;
+
+          sum1 = ip1->checksum;
+          sum1 = ip_csum_update (sum1, old_addr1, new_addr1,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip1->checksum = ip_csum_fold (sum1);
+
+          if (PREDICT_TRUE(proto1 == SNAT_PROTOCOL_TCP))
+            {
+              old_port1 = tcp1->dst_port;
+              tcp1->dst_port = s1->in2out.port;
+              new_port1 = tcp1->dst_port;
+
+              sum1 = tcp1->checksum;
+              sum1 = ip_csum_update (sum1, old_addr1, new_addr1,
+                                     ip4_header_t,
+                                     dst_address /* changed member */);
+
+              sum1 = ip_csum_update (sum1, old_port1, new_port1,
+                                     ip4_header_t /* cheat */,
+                                     length /* changed member */);
+              tcp1->checksum = ip_csum_fold(sum1);
+            }
+          else
+            {
+              old_port1 = udp1->dst_port;
+              udp1->dst_port = s1->in2out.port;
+              udp1->checksum = 0;
+            }
+
+          /* Accounting */
+          s1->last_heard = now;
+          s1->total_pkts++;
+          s1->total_bytes += vlib_buffer_length_in_chain (vm, b1);
+          /* Per-user LRU list maintenance for dynamic translation */
+          if (!snat_is_session_static (s1))
+            {
+              clib_dlist_remove (sm->per_thread_data[thread_index].list_pool,
+                                 s1->per_user_index);
+              clib_dlist_addtail (sm->per_thread_data[thread_index].list_pool,
+                                  s1->per_user_list_head_index,
+                                  s1->per_user_index);
+            }
+        trace1:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b1->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b1, sizeof (*t));
+              t->sw_if_index = sw_if_index1;
+              t->next_index = next1;
+              t->session_index = ~0;
+              if (s1)
+                t->session_index = s1 - sm->per_thread_data[thread_index].sessions;
+            }
+
+          pkts_processed += next1 != SNAT_OUT2IN_NEXT_DROP;
+
+          /* verify speculative enqueues, maybe switch current next frame */
+          vlib_validate_buffer_enqueue_x2 (vm, node, next_index,
+                                           to_next, n_left_to_next,
+                                           bi0, bi1, next0, next1);
+        }
+
+      while (n_left_from > 0 && n_left_to_next > 0)
+	{
+          u32 bi0;
+	  vlib_buffer_t * b0;
+          u32 next0 = SNAT_OUT2IN_NEXT_LOOKUP;
+          u32 sw_if_index0;
+          ip4_header_t * ip0;
+          ip_csum_t sum0;
+          u32 new_addr0, old_addr0;
+          u16 new_port0, old_port0;
+          udp_header_t * udp0;
+          tcp_header_t * tcp0;
+          icmp46_header_t * icmp0;
+          snat_session_key_t key0, sm0;
+          u32 rx_fib_index0;
+          u32 proto0;
+          snat_session_t * s0 = 0;
+          clib_bihash_kv_8_8_t kv0, value0;
+
+          /* speculatively enqueue b0 to the current next frame */
+	  bi0 = from[0];
+	  to_next[0] = bi0;
+	  from += 1;
+	  to_next += 1;
+	  n_left_from -= 1;
+	  n_left_to_next -= 1;
+
+	  b0 = vlib_get_buffer (vm, bi0);
+
+          vnet_buffer (b0)->snat.flags = 0;
+
+          ip0 = vlib_buffer_get_current (b0);
+          udp0 = ip4_next_header (ip0);
+          tcp0 = (tcp_header_t *) udp0;
+          icmp0 = (icmp46_header_t *) udp0;
+
+          sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+	  rx_fib_index0 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index,
+                                   sw_if_index0);
+
+          proto0 = ip_proto_to_snat_proto (ip0->protocol);
+
+          if (PREDICT_FALSE (proto0 == ~0))
+            {
+              snat_out2in_unknown_proto(sm, b0, ip0, rx_fib_index0,
+                                        thread_index, now, vm);
+              goto trace00;
+            }
+
+          if (PREDICT_FALSE(ip0->ttl == 1))
+            {
+              vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace00;
+            }
+
+          if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
+            {
+              next0 = icmp_out2in_slow_path
+                (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
+                 next0, now, thread_index, &s0);
+              goto trace00;
+            }
+
+          key0.addr = ip0->dst_address;
+          key0.port = udp0->dst_port;
+          key0.protocol = proto0;
+          key0.fib_index = rx_fib_index0;
+
+          kv0.key = key0.as_u64;
+
+          if (clib_bihash_search_8_8 (&sm->out2in, &kv0, &value0))
+            {
+              /* Try to match static mapping by external address and port,
+                 destination address and port in packet */
+              if (snat_static_mapping_match(sm, key0, &sm0, 1, 0))
+                {
+                  b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+                  /*
+                   * Send DHCP packets to the ipv4 stack, or we won't
+                   * be able to use dhcp client on the outside interface
+                   */
+                  if (proto0 != SNAT_PROTOCOL_UDP
+                      || (udp0->dst_port
+                          != clib_host_to_net_u16(UDP_DST_PORT_dhcp_to_client)))
+
+                    next0 = SNAT_OUT2IN_NEXT_DROP;
+                  goto trace00;
+                }
+
+              /* Create session initiated by host from external network */
+              s0 = create_session_for_static_mapping(sm, b0, sm0, key0, node,
+                                                     thread_index);
+              if (!s0)
+                {
+                  b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+                    next0 = SNAT_OUT2IN_NEXT_DROP;
+                  goto trace00;
+                }
+            }
+          else
+            s0 = pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
+                                    value0.value);
+
+          old_addr0 = ip0->dst_address.as_u32;
+          ip0->dst_address = s0->in2out.addr;
+          new_addr0 = ip0->dst_address.as_u32;
+          vnet_buffer(b0)->sw_if_index[VLIB_TX] = s0->in2out.fib_index;
+
+          sum0 = ip0->checksum;
+          sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip0->checksum = ip_csum_fold (sum0);
+
+          if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+            {
+              old_port0 = tcp0->dst_port;
+              tcp0->dst_port = s0->in2out.port;
+              new_port0 = tcp0->dst_port;
+
+              sum0 = tcp0->checksum;
+              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                     ip4_header_t,
+                                     dst_address /* changed member */);
+
+              sum0 = ip_csum_update (sum0, old_port0, new_port0,
+                                     ip4_header_t /* cheat */,
+                                     length /* changed member */);
+              tcp0->checksum = ip_csum_fold(sum0);
+            }
+          else
+            {
+              old_port0 = udp0->dst_port;
+              udp0->dst_port = s0->in2out.port;
+              udp0->checksum = 0;
+            }
+
+          /* Accounting */
+          s0->last_heard = now;
+          s0->total_pkts++;
+          s0->total_bytes += vlib_buffer_length_in_chain (vm, b0);
+          /* Per-user LRU list maintenance for dynamic translation */
+          if (!snat_is_session_static (s0))
+            {
+              clib_dlist_remove (sm->per_thread_data[thread_index].list_pool,
+                                 s0->per_user_index);
+              clib_dlist_addtail (sm->per_thread_data[thread_index].list_pool,
+                                  s0->per_user_list_head_index,
+                                  s0->per_user_index);
+            }
+        trace00:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b0, sizeof (*t));
+              t->sw_if_index = sw_if_index0;
+              t->next_index = next0;
+              t->session_index = ~0;
+              if (s0)
+                t->session_index = s0 - sm->per_thread_data[thread_index].sessions;
+            }
+
+          pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;
+
+          /* verify speculative enqueue, maybe switch current next frame */
+	  vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
+					   to_next, n_left_to_next,
+					   bi0, next0);
+	}
+
+      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
+    }
+
+  vlib_node_increment_counter (vm, snat_out2in_node.index,
+                               SNAT_OUT2IN_ERROR_OUT2IN_PACKETS,
+                               pkts_processed);
+  return frame->n_vectors;
+}
+
+VLIB_REGISTER_NODE (snat_out2in_node) = {
+  .function = snat_out2in_node_fn,
+  .name = "nat44-out2in",
+  .vector_size = sizeof (u32),
+  .format_trace = format_snat_out2in_trace,
+  .type = VLIB_NODE_TYPE_INTERNAL,
+
+  .n_errors = ARRAY_LEN(snat_out2in_error_strings),
+  .error_strings = snat_out2in_error_strings,
+
+  .runtime_data_bytes = sizeof (snat_runtime_t),
+
+  .n_next_nodes = SNAT_OUT2IN_N_NEXT,
+
+  /* edit / add dispositions here */
+  .next_nodes = {
+    [SNAT_OUT2IN_NEXT_DROP] = "error-drop",
+    [SNAT_OUT2IN_NEXT_LOOKUP] = "ip4-lookup",
+    [SNAT_OUT2IN_NEXT_ICMP_ERROR] = "ip4-icmp-error",
+  },
+};
+VLIB_NODE_FUNCTION_MULTIARCH (snat_out2in_node, snat_out2in_node_fn);
+
+/**************************/
+/*** deterministic mode ***/
+/**************************/
+static uword
+snat_det_out2in_node_fn (vlib_main_t * vm,
+                         vlib_node_runtime_t * node,
+                         vlib_frame_t * frame)
+{
+  u32 n_left_from, * from, * to_next;
+  snat_out2in_next_t next_index;
+  u32 pkts_processed = 0;
+  snat_main_t * sm = &snat_main;
+  u32 thread_index = vlib_get_thread_index ();
+
+  from = vlib_frame_vector_args (frame);
+  n_left_from = frame->n_vectors;
+  next_index = node->cached_next_index;
+
+  while (n_left_from > 0)
+    {
+      u32 n_left_to_next;
+
+      vlib_get_next_frame (vm, node, next_index,
+			   to_next, n_left_to_next);
+
+      while (n_left_from >= 4 && n_left_to_next >= 2)
+        {
+          u32 bi0, bi1;
+	  vlib_buffer_t * b0, * b1;
+          u32 next0 = SNAT_OUT2IN_NEXT_LOOKUP;
+          u32 next1 = SNAT_OUT2IN_NEXT_LOOKUP;
+          u32 sw_if_index0, sw_if_index1;
+          ip4_header_t * ip0, * ip1;
+          ip_csum_t sum0, sum1;
+          ip4_address_t new_addr0, old_addr0, new_addr1, old_addr1;
+          u16 new_port0, old_port0, old_port1, new_port1;
+          udp_header_t * udp0, * udp1;
+          tcp_header_t * tcp0, * tcp1;
+          u32 proto0, proto1;
+          snat_det_out_key_t key0, key1;
+          snat_det_map_t * dm0, * dm1;
+          snat_det_session_t * ses0 = 0, * ses1 = 0;
+          u32 rx_fib_index0, rx_fib_index1;
+          icmp46_header_t * icmp0, * icmp1;
+
+	  /* Prefetch next iteration. */
+	  {
+	    vlib_buffer_t * p2, * p3;
+
+	    p2 = vlib_get_buffer (vm, from[2]);
+	    p3 = vlib_get_buffer (vm, from[3]);
+
+	    vlib_prefetch_buffer_header (p2, LOAD);
+	    vlib_prefetch_buffer_header (p3, LOAD);
+
+	    CLIB_PREFETCH (p2->data, CLIB_CACHE_LINE_BYTES, STORE);
+	    CLIB_PREFETCH (p3->data, CLIB_CACHE_LINE_BYTES, STORE);
+	  }
+
+          /* speculatively enqueue b0 and b1 to the current next frame */
+	  to_next[0] = bi0 = from[0];
+	  to_next[1] = bi1 = from[1];
+	  from += 2;
+	  to_next += 2;
+	  n_left_from -= 2;
+	  n_left_to_next -= 2;
+
+	  b0 = vlib_get_buffer (vm, bi0);
+	  b1 = vlib_get_buffer (vm, bi1);
+
+          ip0 = vlib_buffer_get_current (b0);
+          udp0 = ip4_next_header (ip0);
+          tcp0 = (tcp_header_t *) udp0;
+
+          sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+
+          if (PREDICT_FALSE(ip0->ttl == 1))
+            {
+              vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace0;
+            }
+
+          proto0 = ip_proto_to_snat_proto (ip0->protocol);
+
+          if (PREDICT_FALSE(proto0 == SNAT_PROTOCOL_ICMP))
+            {
+              rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index(sw_if_index0);
+              icmp0 = (icmp46_header_t *) udp0;
+
+              next0 = icmp_out2in(sm, b0, ip0, icmp0, sw_if_index0,
+                                  rx_fib_index0, node, next0, thread_index,
+                                  &ses0, &dm0);
+              goto trace0;
+            }
+
+          key0.ext_host_addr = ip0->src_address;
+          key0.ext_host_port = tcp0->src;
+          key0.out_port = tcp0->dst;
+
+          dm0 = snat_det_map_by_out(sm, &ip0->dst_address);
+          if (PREDICT_FALSE(!dm0))
+            {
+              clib_warning("unknown dst address:  %U",
+                           format_ip4_address, &ip0->dst_address);
+              next0 = SNAT_OUT2IN_NEXT_DROP;
+              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace0;
+            }
+
+          snat_det_reverse(dm0, &ip0->dst_address,
+                           clib_net_to_host_u16(tcp0->dst), &new_addr0);
+
+          ses0 = snat_det_get_ses_by_out (dm0, &new_addr0, key0.as_u64);
+          if (PREDICT_FALSE(!ses0))
+            {
+              clib_warning("no match src %U:%d dst %U:%d for user %U",
+                           format_ip4_address, &ip0->src_address,
+                           clib_net_to_host_u16 (tcp0->src),
+                           format_ip4_address, &ip0->dst_address,
+                           clib_net_to_host_u16 (tcp0->dst),
+                           format_ip4_address, &new_addr0);
+              next0 = SNAT_OUT2IN_NEXT_DROP;
+              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace0;
+            }
+          new_port0 = ses0->in_port;
+
+          old_addr0 = ip0->dst_address;
+          ip0->dst_address = new_addr0;
+          vnet_buffer(b0)->sw_if_index[VLIB_TX] = sm->inside_fib_index;
+
+          sum0 = ip0->checksum;
+          sum0 = ip_csum_update (sum0, old_addr0.as_u32, new_addr0.as_u32,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip0->checksum = ip_csum_fold (sum0);
+
+          if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+            {
+              if (tcp0->flags & TCP_FLAG_FIN && ses0->state == SNAT_SESSION_TCP_ESTABLISHED)
+                ses0->state = SNAT_SESSION_TCP_CLOSE_WAIT;
+              else if (tcp0->flags & TCP_FLAG_ACK && ses0->state == SNAT_SESSION_TCP_LAST_ACK)
+                snat_det_ses_close(dm0, ses0);
+
+              old_port0 = tcp0->dst;
+              tcp0->dst = new_port0;
+
+              sum0 = tcp0->checksum;
+              sum0 = ip_csum_update (sum0, old_addr0.as_u32, new_addr0.as_u32,
+                                     ip4_header_t,
+                                     dst_address /* changed member */);
+
+              sum0 = ip_csum_update (sum0, old_port0, new_port0,
+                                     ip4_header_t /* cheat */,
+                                     length /* changed member */);
+              tcp0->checksum = ip_csum_fold(sum0);
+            }
+          else
+            {
+              old_port0 = udp0->dst_port;
+              udp0->dst_port = new_port0;
+              udp0->checksum = 0;
+            }
+
+        trace0:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b0, sizeof (*t));
+              t->sw_if_index = sw_if_index0;
+              t->next_index = next0;
+              t->session_index = ~0;
+              if (ses0)
+                t->session_index = ses0 - dm0->sessions;
+            }
+
+          pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;
+
+	  b1 = vlib_get_buffer (vm, bi1);
+
+          ip1 = vlib_buffer_get_current (b1);
+          udp1 = ip4_next_header (ip1);
+          tcp1 = (tcp_header_t *) udp1;
+
+          sw_if_index1 = vnet_buffer(b1)->sw_if_index[VLIB_RX];
+
+          if (PREDICT_FALSE(ip1->ttl == 1))
+            {
+              vnet_buffer (b1)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b1, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next1 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace1;
+            }
+
+          proto1 = ip_proto_to_snat_proto (ip1->protocol);
+
+          if (PREDICT_FALSE(proto1 == SNAT_PROTOCOL_ICMP))
+            {
+              rx_fib_index1 = ip4_fib_table_get_index_for_sw_if_index(sw_if_index1);
+              icmp1 = (icmp46_header_t *) udp1;
+
+              next1 = icmp_out2in(sm, b1, ip1, icmp1, sw_if_index1,
+                                  rx_fib_index1, node, next1, thread_index,
+                                  &ses1, &dm1);
+              goto trace1;
+            }
+
+          key1.ext_host_addr = ip1->src_address;
+          key1.ext_host_port = tcp1->src;
+          key1.out_port = tcp1->dst;
+
+          dm1 = snat_det_map_by_out(sm, &ip1->dst_address);
+          if (PREDICT_FALSE(!dm1))
+            {
+              clib_warning("unknown dst address:  %U",
+                           format_ip4_address, &ip1->dst_address);
+              next1 = SNAT_OUT2IN_NEXT_DROP;
+              b1->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace1;
+            }
+
+          snat_det_reverse(dm1, &ip1->dst_address,
+                           clib_net_to_host_u16(tcp1->dst), &new_addr1);
+
+          ses1 = snat_det_get_ses_by_out (dm1, &new_addr1, key1.as_u64);
+          if (PREDICT_FALSE(!ses1))
+            {
+              clib_warning("no match src %U:%d dst %U:%d for user %U",
+                           format_ip4_address, &ip1->src_address,
+                           clib_net_to_host_u16 (tcp1->src),
+                           format_ip4_address, &ip1->dst_address,
+                           clib_net_to_host_u16 (tcp1->dst),
+                           format_ip4_address, &new_addr1);
+              next1 = SNAT_OUT2IN_NEXT_DROP;
+              b1->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace1;
+            }
+          new_port1 = ses1->in_port;
+
+          old_addr1 = ip1->dst_address;
+          ip1->dst_address = new_addr1;
+          vnet_buffer(b1)->sw_if_index[VLIB_TX] = sm->inside_fib_index;
+
+          sum1 = ip1->checksum;
+          sum1 = ip_csum_update (sum1, old_addr1.as_u32, new_addr1.as_u32,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip1->checksum = ip_csum_fold (sum1);
+
+          if (PREDICT_TRUE(proto1 == SNAT_PROTOCOL_TCP))
+            {
+              if (tcp1->flags & TCP_FLAG_FIN && ses1->state == SNAT_SESSION_TCP_ESTABLISHED)
+                ses1->state = SNAT_SESSION_TCP_CLOSE_WAIT;
+              else if (tcp1->flags & TCP_FLAG_ACK && ses1->state == SNAT_SESSION_TCP_LAST_ACK)
+                snat_det_ses_close(dm1, ses1);
+
+              old_port1 = tcp1->dst;
+              tcp1->dst = new_port1;
+
+              sum1 = tcp1->checksum;
+              sum1 = ip_csum_update (sum1, old_addr1.as_u32, new_addr1.as_u32,
+                                     ip4_header_t,
+                                     dst_address /* changed member */);
+
+              sum1 = ip_csum_update (sum1, old_port1, new_port1,
+                                     ip4_header_t /* cheat */,
+                                     length /* changed member */);
+              tcp1->checksum = ip_csum_fold(sum1);
+            }
+          else
+            {
+              old_port1 = udp1->dst_port;
+              udp1->dst_port = new_port1;
+              udp1->checksum = 0;
+            }
+
+        trace1:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b1->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b1, sizeof (*t));
+              t->sw_if_index = sw_if_index1;
+              t->next_index = next1;
+              t->session_index = ~0;
+              if (ses1)
+                t->session_index = ses1 - dm1->sessions;
+            }
+
+          pkts_processed += next1 != SNAT_OUT2IN_NEXT_DROP;
+
+          /* verify speculative enqueues, maybe switch current next frame */
+          vlib_validate_buffer_enqueue_x2 (vm, node, next_index,
+                                           to_next, n_left_to_next,
+                                           bi0, bi1, next0, next1);
+         }
+
+      while (n_left_from > 0 && n_left_to_next > 0)
+	{
+          u32 bi0;
+	  vlib_buffer_t * b0;
+          u32 next0 = SNAT_OUT2IN_NEXT_LOOKUP;
+          u32 sw_if_index0;
+          ip4_header_t * ip0;
+          ip_csum_t sum0;
+          ip4_address_t new_addr0, old_addr0;
+          u16 new_port0, old_port0;
+          udp_header_t * udp0;
+          tcp_header_t * tcp0;
+          u32 proto0;
+          snat_det_out_key_t key0;
+          snat_det_map_t * dm0;
+          snat_det_session_t * ses0 = 0;
+          u32 rx_fib_index0;
+          icmp46_header_t * icmp0;
+
+          /* speculatively enqueue b0 to the current next frame */
+	  bi0 = from[0];
+	  to_next[0] = bi0;
+	  from += 1;
+	  to_next += 1;
+	  n_left_from -= 1;
+	  n_left_to_next -= 1;
+
+	  b0 = vlib_get_buffer (vm, bi0);
+
+          ip0 = vlib_buffer_get_current (b0);
+          udp0 = ip4_next_header (ip0);
+          tcp0 = (tcp_header_t *) udp0;
+
+          sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+
+          if (PREDICT_FALSE(ip0->ttl == 1))
+            {
+              vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace00;
+            }
+
+          proto0 = ip_proto_to_snat_proto (ip0->protocol);
+
+          if (PREDICT_FALSE(proto0 == SNAT_PROTOCOL_ICMP))
+            {
+              rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index(sw_if_index0);
+              icmp0 = (icmp46_header_t *) udp0;
+
+              next0 = icmp_out2in(sm, b0, ip0, icmp0, sw_if_index0,
+                                  rx_fib_index0, node, next0, thread_index,
+                                  &ses0, &dm0);
+              goto trace00;
+            }
+
+          key0.ext_host_addr = ip0->src_address;
+          key0.ext_host_port = tcp0->src;
+          key0.out_port = tcp0->dst;
+
+          dm0 = snat_det_map_by_out(sm, &ip0->dst_address);
+          if (PREDICT_FALSE(!dm0))
+            {
+              clib_warning("unknown dst address:  %U",
+                           format_ip4_address, &ip0->dst_address);
+              next0 = SNAT_OUT2IN_NEXT_DROP;
+              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace00;
+            }
+
+          snat_det_reverse(dm0, &ip0->dst_address,
+                           clib_net_to_host_u16(tcp0->dst), &new_addr0);
+
+          ses0 = snat_det_get_ses_by_out (dm0, &new_addr0, key0.as_u64);
+          if (PREDICT_FALSE(!ses0))
+            {
+              clib_warning("no match src %U:%d dst %U:%d for user %U",
+                           format_ip4_address, &ip0->src_address,
+                           clib_net_to_host_u16 (tcp0->src),
+                           format_ip4_address, &ip0->dst_address,
+                           clib_net_to_host_u16 (tcp0->dst),
+                           format_ip4_address, &new_addr0);
+              next0 = SNAT_OUT2IN_NEXT_DROP;
+              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace00;
+            }
+          new_port0 = ses0->in_port;
+
+          old_addr0 = ip0->dst_address;
+          ip0->dst_address = new_addr0;
+          vnet_buffer(b0)->sw_if_index[VLIB_TX] = sm->inside_fib_index;
+
+          sum0 = ip0->checksum;
+          sum0 = ip_csum_update (sum0, old_addr0.as_u32, new_addr0.as_u32,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip0->checksum = ip_csum_fold (sum0);
+
+          if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+            {
+              if (tcp0->flags & TCP_FLAG_FIN && ses0->state == SNAT_SESSION_TCP_ESTABLISHED)
+                ses0->state = SNAT_SESSION_TCP_CLOSE_WAIT;
+              else if (tcp0->flags & TCP_FLAG_ACK && ses0->state == SNAT_SESSION_TCP_LAST_ACK)
+                snat_det_ses_close(dm0, ses0);
+
+              old_port0 = tcp0->dst;
+              tcp0->dst = new_port0;
+
+              sum0 = tcp0->checksum;
+              sum0 = ip_csum_update (sum0, old_addr0.as_u32, new_addr0.as_u32,
+                                     ip4_header_t,
+                                     dst_address /* changed member */);
+
+              sum0 = ip_csum_update (sum0, old_port0, new_port0,
+                                     ip4_header_t /* cheat */,
+                                     length /* changed member */);
+              tcp0->checksum = ip_csum_fold(sum0);
+            }
+          else
+            {
+              old_port0 = udp0->dst_port;
+              udp0->dst_port = new_port0;
+              udp0->checksum = 0;
+            }
+
+        trace00:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b0, sizeof (*t));
+              t->sw_if_index = sw_if_index0;
+              t->next_index = next0;
+              t->session_index = ~0;
+              if (ses0)
+                t->session_index = ses0 - dm0->sessions;
+            }
+
+          pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;
+
+          /* verify speculative enqueue, maybe switch current next frame */
+	  vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
+					   to_next, n_left_to_next,
+					   bi0, next0);
+	}
+
+      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
+    }
+
+  vlib_node_increment_counter (vm, snat_det_out2in_node.index,
+                               SNAT_OUT2IN_ERROR_OUT2IN_PACKETS,
+                               pkts_processed);
+  return frame->n_vectors;
+}
+
+VLIB_REGISTER_NODE (snat_det_out2in_node) = {
+  .function = snat_det_out2in_node_fn,
+  .name = "nat44-det-out2in",
+  .vector_size = sizeof (u32),
+  .format_trace = format_snat_out2in_trace,
+  .type = VLIB_NODE_TYPE_INTERNAL,
+
+  .n_errors = ARRAY_LEN(snat_out2in_error_strings),
+  .error_strings = snat_out2in_error_strings,
+
+  .runtime_data_bytes = sizeof (snat_runtime_t),
+
+  .n_next_nodes = SNAT_OUT2IN_N_NEXT,
+
+  /* edit / add dispositions here */
+  .next_nodes = {
+    [SNAT_OUT2IN_NEXT_DROP] = "error-drop",
+    [SNAT_OUT2IN_NEXT_LOOKUP] = "ip4-lookup",
+    [SNAT_OUT2IN_NEXT_ICMP_ERROR] = "ip4-icmp-error",
+  },
+};
+VLIB_NODE_FUNCTION_MULTIARCH (snat_det_out2in_node, snat_det_out2in_node_fn);
+
+/**
+ * Get address and port values to be used for ICMP packet translation
+ * and create session if needed
+ *
+ * @param[in,out] sm             NAT main
+ * @param[in,out] node           NAT node runtime
+ * @param[in] thread_index       thread index
+ * @param[in,out] b0             buffer containing packet to be translated
+ * @param[out] p_proto           protocol used for matching
+ * @param[out] p_value           address and port after NAT translation
+ * @param[out] p_dont_translate  if packet should not be translated
+ * @param d                      optional parameter
+ * @param e                      optional parameter
+ */
+u32 icmp_match_out2in_det(snat_main_t *sm, vlib_node_runtime_t *node,
+                          u32 thread_index, vlib_buffer_t *b0, u8 *p_proto,
+                          snat_session_key_t *p_value,
+                          u8 *p_dont_translate, void *d, void *e)
+{
+  ip4_header_t *ip0;
+  icmp46_header_t *icmp0;
+  u32 sw_if_index0;
+  u8 protocol;
+  snat_det_out_key_t key0;
+  u8 dont_translate = 0;
+  u32 next0 = ~0;
+  icmp_echo_header_t *echo0, *inner_echo0 = 0;
+  ip4_header_t *inner_ip0;
+  void *l4_header = 0;
+  icmp46_header_t *inner_icmp0;
+  snat_det_map_t * dm0 = 0;
+  ip4_address_t new_addr0 = {{0}};
+  snat_det_session_t * ses0 = 0;
+  ip4_address_t out_addr;
+
+  ip0 = vlib_buffer_get_current (b0);
+  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
+  echo0 = (icmp_echo_header_t *)(icmp0+1);
+  sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+
+  if (!icmp_is_error_message (icmp0))
+    {
+      protocol = SNAT_PROTOCOL_ICMP;
+      key0.ext_host_addr = ip0->src_address;
+      key0.ext_host_port = 0;
+      key0.out_port = echo0->identifier;
+      out_addr = ip0->dst_address;
+    }
+  else
+    {
+      inner_ip0 = (ip4_header_t *)(echo0+1);
+      l4_header = ip4_next_header (inner_ip0);
+      protocol = ip_proto_to_snat_proto (inner_ip0->protocol);
+      key0.ext_host_addr = inner_ip0->dst_address;
+      out_addr = inner_ip0->src_address;
+      switch (protocol)
+        {
+        case SNAT_PROTOCOL_ICMP:
+          inner_icmp0 = (icmp46_header_t*)l4_header;
+          inner_echo0 = (icmp_echo_header_t *)(inner_icmp0+1);
+          key0.ext_host_port = 0;
+          key0.out_port = inner_echo0->identifier;
+          break;
+        case SNAT_PROTOCOL_UDP:
+        case SNAT_PROTOCOL_TCP:
+          key0.ext_host_port = ((tcp_udp_header_t*)l4_header)->dst_port;
+          key0.out_port = ((tcp_udp_header_t*)l4_header)->src_port;
+          break;
+        default:
+          b0->error = node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
+          next0 = SNAT_OUT2IN_NEXT_DROP;
+          goto out;
+        }
+    }
+
+  dm0 = snat_det_map_by_out(sm, &out_addr);
+  if (PREDICT_FALSE(!dm0))
+    {
+      /* Don't NAT packet aimed at the intfc address */
+      if (PREDICT_FALSE(is_interface_addr(sm, node, sw_if_index0,
+                                          ip0->dst_address.as_u32)))
+        {
+          dont_translate = 1;
+          goto out;
+        }
+      clib_warning("unknown dst address:  %U",
+                   format_ip4_address, &ip0->dst_address);
+      goto out;
+    }
+
+  snat_det_reverse(dm0, &ip0->dst_address,
+                   clib_net_to_host_u16(key0.out_port), &new_addr0);
+
+  ses0 = snat_det_get_ses_by_out (dm0, &new_addr0, key0.as_u64);
+  if (PREDICT_FALSE(!ses0))
+    {
+      /* Don't NAT packet aimed at the intfc address */
+      if (PREDICT_FALSE(is_interface_addr(sm, node, sw_if_index0,
+                                          ip0->dst_address.as_u32)))
+        {
+          dont_translate = 1;
+          goto out;
+        }
+      clib_warning("no match src %U:%d dst %U:%d for user %U",
+                   format_ip4_address, &key0.ext_host_addr,
+                   clib_net_to_host_u16 (key0.ext_host_port),
+                   format_ip4_address, &out_addr,
+                   clib_net_to_host_u16 (key0.out_port),
+                   format_ip4_address, &new_addr0);
+      b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out;
+    }
+
+  if (PREDICT_FALSE(icmp0->type != ICMP4_echo_reply &&
+                    !icmp_is_error_message (icmp0)))
+    {
+      b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
+      next0 = SNAT_OUT2IN_NEXT_DROP;
+      goto out;
+    }
+
+  goto out;
+
+out:
+  *p_proto = protocol;
+  if (ses0)
+    {
+      p_value->addr = new_addr0;
+      p_value->fib_index = sm->inside_fib_index;
+      p_value->port = ses0->in_port;
+    }
+  *p_dont_translate = dont_translate;
+  if (d)
+    *(snat_det_session_t**)d = ses0;
+  if (e)
+    *(snat_det_map_t**)e = dm0;
+  return next0;
+}
+
+/**********************/
+/*** worker handoff ***/
+/**********************/
+static uword
+snat_out2in_worker_handoff_fn (vlib_main_t * vm,
+                               vlib_node_runtime_t * node,
+                               vlib_frame_t * frame)
+{
+  snat_main_t *sm = &snat_main;
+  vlib_thread_main_t *tm = vlib_get_thread_main ();
+  u32 n_left_from, *from, *to_next = 0;
+  static __thread vlib_frame_queue_elt_t **handoff_queue_elt_by_worker_index;
+  static __thread vlib_frame_queue_t **congested_handoff_queue_by_worker_index
+    = 0;
+  vlib_frame_queue_elt_t *hf = 0;
+  vlib_frame_t *f = 0;
+  int i;
+  u32 n_left_to_next_worker = 0, *to_next_worker = 0;
+  u32 next_worker_index = 0;
+  u32 current_worker_index = ~0;
+  u32 thread_index = vlib_get_thread_index ();
+
+  ASSERT (vec_len (sm->workers));
+
+  if (PREDICT_FALSE (handoff_queue_elt_by_worker_index == 0))
+    {
+      vec_validate (handoff_queue_elt_by_worker_index, tm->n_vlib_mains - 1);
+
+      vec_validate_init_empty (congested_handoff_queue_by_worker_index,
+			       sm->first_worker_index + sm->num_workers - 1,
+			       (vlib_frame_queue_t *) (~0));
+    }
+
+  from = vlib_frame_vector_args (frame);
+  n_left_from = frame->n_vectors;
+
+  while (n_left_from > 0)
+    {
+      u32 bi0;
+      vlib_buffer_t *b0;
+      u32 sw_if_index0;
+      u32 rx_fib_index0;
+      ip4_header_t * ip0;
+      u8 do_handoff;
+
+      bi0 = from[0];
+      from += 1;
+      n_left_from -= 1;
+
+      b0 = vlib_get_buffer (vm, bi0);
+
+      sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
+      rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index(sw_if_index0);
+
+      ip0 = vlib_buffer_get_current (b0);
+
+      next_worker_index = sm->worker_out2in_cb(ip0, rx_fib_index0);
+
+      if (PREDICT_FALSE (next_worker_index != thread_index))
+        {
+          do_handoff = 1;
+
+          if (next_worker_index != current_worker_index)
+            {
+              if (hf)
+                hf->n_vectors = VLIB_FRAME_SIZE - n_left_to_next_worker;
+
+              hf = vlib_get_worker_handoff_queue_elt (sm->fq_out2in_index,
+                                                      next_worker_index,
+                                                      handoff_queue_elt_by_worker_index);
+
+              n_left_to_next_worker = VLIB_FRAME_SIZE - hf->n_vectors;
+              to_next_worker = &hf->buffer_index[hf->n_vectors];
+              current_worker_index = next_worker_index;
+            }
+
+          /* enqueue to correct worker thread */
+          to_next_worker[0] = bi0;
+          to_next_worker++;
+          n_left_to_next_worker--;
+
+          if (n_left_to_next_worker == 0)
+            {
+              hf->n_vectors = VLIB_FRAME_SIZE;
+              vlib_put_frame_queue_elt (hf);
+              current_worker_index = ~0;
+              handoff_queue_elt_by_worker_index[next_worker_index] = 0;
+              hf = 0;
+            }
+        }
+      else
+        {
+          do_handoff = 0;
+          /* if this is 1st frame */
+          if (!f)
+            {
+              f = vlib_get_frame_to_node (vm, sm->out2in_node_index);
+              to_next = vlib_frame_vector_args (f);
+            }
+
+          to_next[0] = bi0;
+          to_next += 1;
+          f->n_vectors++;
+        }
+
+      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
+			 && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+	{
+          snat_out2in_worker_handoff_trace_t *t =
+            vlib_add_trace (vm, node, b0, sizeof (*t));
+          t->next_worker_index = next_worker_index;
+          t->do_handoff = do_handoff;
+        }
+    }
+
+  if (f)
+    vlib_put_frame_to_node (vm, sm->out2in_node_index, f);
+
+  if (hf)
+    hf->n_vectors = VLIB_FRAME_SIZE - n_left_to_next_worker;
+
+  /* Ship frames to the worker nodes */
+  for (i = 0; i < vec_len (handoff_queue_elt_by_worker_index); i++)
+    {
+      if (handoff_queue_elt_by_worker_index[i])
+	{
+	  hf = handoff_queue_elt_by_worker_index[i];
+	  /*
+	   * It works better to let the handoff node
+	   * rate-adapt, always ship the handoff queue element.
+	   */
+	  if (1 || hf->n_vectors == hf->last_n_vectors)
+	    {
+	      vlib_put_frame_queue_elt (hf);
+	      handoff_queue_elt_by_worker_index[i] = 0;
+	    }
+	  else
+	    hf->last_n_vectors = hf->n_vectors;
+	}
+      congested_handoff_queue_by_worker_index[i] =
+	(vlib_frame_queue_t *) (~0);
+    }
+  hf = 0;
+  current_worker_index = ~0;
+  return frame->n_vectors;
+}
+
+VLIB_REGISTER_NODE (snat_out2in_worker_handoff_node) = {
+  .function = snat_out2in_worker_handoff_fn,
+  .name = "nat44-out2in-worker-handoff",
+  .vector_size = sizeof (u32),
+  .format_trace = format_snat_out2in_worker_handoff_trace,
+  .type = VLIB_NODE_TYPE_INTERNAL,
+
+  .n_next_nodes = 1,
+
+  .next_nodes = {
+    [0] = "error-drop",
+  },
+};
+
+VLIB_NODE_FUNCTION_MULTIARCH (snat_out2in_worker_handoff_node, snat_out2in_worker_handoff_fn);
+
+static uword
+snat_out2in_fast_node_fn (vlib_main_t * vm,
+                          vlib_node_runtime_t * node,
+		          vlib_frame_t * frame)
+{
+  u32 n_left_from, * from, * to_next;
+  snat_out2in_next_t next_index;
+  u32 pkts_processed = 0;
+  snat_main_t * sm = &snat_main;
+
+  from = vlib_frame_vector_args (frame);
+  n_left_from = frame->n_vectors;
+  next_index = node->cached_next_index;
+
+  while (n_left_from > 0)
+    {
+      u32 n_left_to_next;
+
+      vlib_get_next_frame (vm, node, next_index,
+			   to_next, n_left_to_next);
+
+      while (n_left_from > 0 && n_left_to_next > 0)
+	{
+          u32 bi0;
+	  vlib_buffer_t * b0;
+          u32 next0 = SNAT_OUT2IN_NEXT_DROP;
+          u32 sw_if_index0;
+          ip4_header_t * ip0;
+          ip_csum_t sum0;
+          u32 new_addr0, old_addr0;
+          u16 new_port0, old_port0;
+          udp_header_t * udp0;
+          tcp_header_t * tcp0;
+          icmp46_header_t * icmp0;
+          snat_session_key_t key0, sm0;
+          u32 proto0;
+          u32 rx_fib_index0;
+
+          /* speculatively enqueue b0 to the current next frame */
+	  bi0 = from[0];
+	  to_next[0] = bi0;
+	  from += 1;
+	  to_next += 1;
+	  n_left_from -= 1;
+	  n_left_to_next -= 1;
+
+	  b0 = vlib_get_buffer (vm, bi0);
+
+          ip0 = vlib_buffer_get_current (b0);
+          udp0 = ip4_next_header (ip0);
+          tcp0 = (tcp_header_t *) udp0;
+          icmp0 = (icmp46_header_t *) udp0;
+
+          sw_if_index0 = vnet_buffer(b0)->sw_if_index[VLIB_RX];
+	  rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index(sw_if_index0);
+
+	  vnet_feature_next (sw_if_index0, &next0, b0);
+
+          if (PREDICT_FALSE(ip0->ttl == 1))
+            {
+              vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
+              icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
+                                           ICMP4_time_exceeded_ttl_exceeded_in_transit,
+                                           0);
+              next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
+              goto trace00;
+            }
+
+          proto0 = ip_proto_to_snat_proto (ip0->protocol);
+
+          if (PREDICT_FALSE (proto0 == ~0))
+              goto trace00;
+
+          if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
+            {
+              next0 = icmp_out2in(sm, b0, ip0, icmp0, sw_if_index0,
+                                  rx_fib_index0, node, next0, ~0, 0, 0);
+              goto trace00;
+            }
+
+          key0.addr = ip0->dst_address;
+          key0.port = udp0->dst_port;
+          key0.fib_index = rx_fib_index0;
+
+          if (snat_static_mapping_match(sm, key0, &sm0, 1, 0))
+            {
+              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
+              goto trace00;
+            }
+
+          new_addr0 = sm0.addr.as_u32;
+          new_port0 = sm0.port;
+          vnet_buffer(b0)->sw_if_index[VLIB_TX] = sm0.fib_index;
+          old_addr0 = ip0->dst_address.as_u32;
+          ip0->dst_address.as_u32 = new_addr0;
+
+          sum0 = ip0->checksum;
+          sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                 ip4_header_t,
+                                 dst_address /* changed member */);
+          ip0->checksum = ip_csum_fold (sum0);
+
+          if (PREDICT_FALSE(new_port0 != udp0->dst_port))
+            {
+               if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+                {
+                  old_port0 = tcp0->dst_port;
+                  tcp0->dst_port = new_port0;
+
+                  sum0 = tcp0->checksum;
+                  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                         ip4_header_t,
+                                         dst_address /* changed member */);
+
+                  sum0 = ip_csum_update (sum0, old_port0, new_port0,
+                                         ip4_header_t /* cheat */,
+                                         length /* changed member */);
+                  tcp0->checksum = ip_csum_fold(sum0);
+                }
+              else
+                {
+                  old_port0 = udp0->dst_port;
+                  udp0->dst_port = new_port0;
+                  udp0->checksum = 0;
+                }
+            }
+          else
+            {
+              if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+                {
+                  sum0 = tcp0->checksum;
+                  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+                                         ip4_header_t,
+                                         dst_address /* changed member */);
+
+                  tcp0->checksum = ip_csum_fold(sum0);
+                }
+            }
+
+        trace00:
+
+          if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
+                            && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+            {
+              snat_out2in_trace_t *t =
+                 vlib_add_trace (vm, node, b0, sizeof (*t));
+              t->sw_if_index = sw_if_index0;
+              t->next_index = next0;
+            }
+
+          pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;
+
+          /* verify speculative enqueue, maybe switch current next frame */
+	  vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
+					   to_next, n_left_to_next,
+					   bi0, next0);
+	}
+
+      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
+    }
+
+  vlib_node_increment_counter (vm, snat_out2in_fast_node.index,
+                               SNAT_OUT2IN_ERROR_OUT2IN_PACKETS,
+                               pkts_processed);
+  return frame->n_vectors;
+}
+
+VLIB_REGISTER_NODE (snat_out2in_fast_node) = {
+  .function = snat_out2in_fast_node_fn,
+  .name = "nat44-out2in-fast",
+  .vector_size = sizeof (u32),
+  .format_trace = format_snat_out2in_fast_trace,
+  .type = VLIB_NODE_TYPE_INTERNAL,
+
+  .n_errors = ARRAY_LEN(snat_out2in_error_strings),
+  .error_strings = snat_out2in_error_strings,
+
+  .runtime_data_bytes = sizeof (snat_runtime_t),
+
+  .n_next_nodes = SNAT_OUT2IN_N_NEXT,
+
+  /* edit / add dispositions here */
+  .next_nodes = {
+    [SNAT_OUT2IN_NEXT_LOOKUP] = "ip4-lookup",
+    [SNAT_OUT2IN_NEXT_DROP] = "error-drop",
+    [SNAT_OUT2IN_NEXT_ICMP_ERROR] = "ip4-icmp-error",
+  },
+};
+VLIB_NODE_FUNCTION_MULTIARCH (snat_out2in_fast_node, snat_out2in_fast_node_fn);