One armed NAT (VPP-1035)

Use a single physical interface in order to accomplish NAT44/NAT64.

Change-Id: I0c8138953a7a4075df306172e125abad771315e4
Signed-off-by: Matus Fabian <matfabia@cisco.com>

8 files changed, 289 insertions, 33 deletions

diff --git a/src/plugins/nat/in2out.c b/src/plugins/nat/in2out.c
index 24ff38602c5..9f668d89f97 100755
--- a/src/plugins/nat/in2out.c
+++ b/src/plugins/nat/in2out.c
@@ -182,7 +182,7 @@ snat_not_translate_fast (snat_main_t * sm, vlib_node_runtime_t *node,
       pool_foreach (i, sm->interfaces,
       ({
         /* NAT packet aimed at outside interface */
-        if ((i->is_inside == 0) && (sw_if_index == i->sw_if_index))
+        if ((nat_interface_is_outside(i)) && (sw_if_index == i->sw_if_index))
           return 0;
       }));
     }
@@ -3523,7 +3523,7 @@ snat_hairpin_src_fn (vlib_main_t * vm,
           pool_foreach (i, sm->output_feature_interfaces,
           ({
             /* Only packets from NAT inside interface */
-            if ((i->is_inside == 1) && (sw_if_index0 == i->sw_if_index))
+            if ((nat_interface_is_inside(i)) && (sw_if_index0 == i->sw_if_index))
               {
                 if (PREDICT_FALSE ((vnet_buffer (b0)->snat.flags) &
                                     SNAT_FLAG_HAIRPINNING))
diff --git a/src/plugins/nat/nat.api b/src/plugins/nat/nat.api
index 84187578c9d..fe408211d83 100644
--- a/src/plugins/nat/nat.api
+++ b/src/plugins/nat/nat.api
@@ -827,7 +827,7 @@ define nat44_interface_dump {
 
 /** \brief NAT44 interface details response
     @param context - sender context, to match reply w/ request
-    @param is_inside - 1 if inside, 0 if outside
+    @param is_inside - 1 if inside, 0 if outside, 2 if inside and outside
     @param sw_if_index - software index of the interface
 */
 define nat44_interface_details {
diff --git a/src/plugins/nat/nat.c b/src/plugins/nat/nat.c
index 887fab78779..50ab317759e 100644
--- a/src/plugins/nat/nat.c
+++ b/src/plugins/nat/nat.c
@@ -42,6 +42,11 @@ VNET_FEATURE_INIT (ip4_snat_out2in, static) = {
   .node_name = "nat44-out2in",
   .runs_before = VNET_FEATURES ("ip4-lookup"),
 };
+VNET_FEATURE_INIT (ip4_nat_classify, static) = {
+  .arc_name = "ip4-unicast",
+  .node_name = "nat44-classify",
+  .runs_before = VNET_FEATURES ("ip4-lookup"),
+};
 VNET_FEATURE_INIT (ip4_snat_det_in2out, static) = {
   .arc_name = "ip4-unicast",
   .node_name = "nat44-det-in2out",
@@ -52,6 +57,11 @@ VNET_FEATURE_INIT (ip4_snat_det_out2in, static) = {
   .node_name = "nat44-det-out2in",
   .runs_before = VNET_FEATURES ("ip4-lookup"),
 };
+VNET_FEATURE_INIT (ip4_nat_det_classify, static) = {
+  .arc_name = "ip4-unicast",
+  .node_name = "nat44-det-classify",
+  .runs_before = VNET_FEATURES ("ip4-lookup"),
+};
 VNET_FEATURE_INIT (ip4_snat_in2out_worker_handoff, static) = {
   .arc_name = "ip4-unicast",
   .node_name = "nat44-in2out-worker-handoff",
@@ -62,6 +72,11 @@ VNET_FEATURE_INIT (ip4_snat_out2in_worker_handoff, static) = {
   .node_name = "nat44-out2in-worker-handoff",
   .runs_before = VNET_FEATURES ("ip4-lookup"),
 };
+VNET_FEATURE_INIT (ip4_nat_handoff_classify, static) = {
+  .arc_name = "ip4-unicast",
+  .node_name = "nat44-handoff-classify",
+  .runs_before = VNET_FEATURES ("ip4-lookup"),
+};
 VNET_FEATURE_INIT (ip4_snat_in2out_fast, static) = {
   .arc_name = "ip4-unicast",
   .node_name = "nat44-in2out-fast",
@@ -111,6 +126,159 @@ VLIB_PLUGIN_REGISTER () = {
 };
 /* *INDENT-ON* */
 
+vlib_node_registration_t nat44_classify_node;
+vlib_node_registration_t nat44_det_classify_node;
+vlib_node_registration_t nat44_handoff_classify_node;
+
+typedef enum {
+  NAT44_CLASSIFY_NEXT_IN2OUT,
+  NAT44_CLASSIFY_NEXT_OUT2IN,
+  NAT44_CLASSIFY_N_NEXT,
+} nat44_classify_next_t;
+
+static inline uword
+nat44_classify_node_fn_inline (vlib_main_t * vm,
+                               vlib_node_runtime_t * node,
+                               vlib_frame_t * frame)
+{
+  u32 n_left_from, * from, * to_next;
+  nat44_classify_next_t next_index;
+  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 = NAT44_CLASSIFY_NEXT_IN2OUT;
+          ip4_header_t *ip0;
+          snat_address_t *ap;
+          snat_session_key_t m_key0;
+          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);
+          ip0 = vlib_buffer_get_current (b0);
+
+          vec_foreach (ap, sm->addresses)
+            {
+              if (ip0->dst_address.as_u32 == ap->addr.as_u32)
+                {
+                  next0 = NAT44_CLASSIFY_NEXT_OUT2IN;
+                  break;
+                }
+            }
+
+          if (PREDICT_FALSE (pool_elts (sm->static_mappings)))
+            {
+              m_key0.addr = ip0->dst_address;
+              m_key0.port = 0;
+              m_key0.protocol = 0;
+              m_key0.fib_index = sm->outside_fib_index;
+              kv0.key = m_key0.as_u64;
+              if (!clib_bihash_search_8_8 (&sm->static_mapping_by_external, &kv0, &value0))
+                {
+                  next0 = NAT44_CLASSIFY_NEXT_OUT2IN;
+                }
+            }
+          /* 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);
+    }
+
+  return frame->n_vectors;
+}
+
+static uword
+nat44_classify_node_fn (vlib_main_t * vm,
+                        vlib_node_runtime_t * node,
+                        vlib_frame_t * frame)
+{
+  return nat44_classify_node_fn_inline (vm, node, frame);
+};
+
+VLIB_REGISTER_NODE (nat44_classify_node) = {
+  .function = nat44_classify_node_fn,
+  .name = "nat44-classify",
+  .vector_size = sizeof (u32),
+  .type = VLIB_NODE_TYPE_INTERNAL,
+  .n_next_nodes = NAT44_CLASSIFY_N_NEXT,
+  .next_nodes = {
+    [NAT44_CLASSIFY_NEXT_IN2OUT] = "nat44-in2out",
+    [NAT44_CLASSIFY_NEXT_OUT2IN] = "nat44-out2in",
+  },
+};
+
+VLIB_NODE_FUNCTION_MULTIARCH (nat44_classify_node,
+                              nat44_classify_node_fn);
+
+static uword
+nat44_det_classify_node_fn (vlib_main_t * vm,
+                            vlib_node_runtime_t * node,
+                            vlib_frame_t * frame)
+{
+  return nat44_classify_node_fn_inline (vm, node, frame);
+};
+
+VLIB_REGISTER_NODE (nat44_det_classify_node) = {
+  .function = nat44_det_classify_node_fn,
+  .name = "nat44-det-classify",
+  .vector_size = sizeof (u32),
+  .type = VLIB_NODE_TYPE_INTERNAL,
+  .n_next_nodes = NAT44_CLASSIFY_N_NEXT,
+  .next_nodes = {
+    [NAT44_CLASSIFY_NEXT_IN2OUT] = "nat44-det-in2out",
+    [NAT44_CLASSIFY_NEXT_OUT2IN] = "nat44-det-out2in",
+  },
+};
+
+VLIB_NODE_FUNCTION_MULTIARCH (nat44_det_classify_node,
+                              nat44_det_classify_node_fn);
+
+static uword
+nat44_handoff_classify_node_fn (vlib_main_t * vm,
+                                vlib_node_runtime_t * node,
+                                vlib_frame_t * frame)
+{
+  return nat44_classify_node_fn_inline (vm, node, frame);
+};
+
+VLIB_REGISTER_NODE (nat44_handoff_classify_node) = {
+  .function = nat44_handoff_classify_node_fn,
+  .name = "nat44-handoff-classify",
+  .vector_size = sizeof (u32),
+  .type = VLIB_NODE_TYPE_INTERNAL,
+  .n_next_nodes = NAT44_CLASSIFY_N_NEXT,
+  .next_nodes = {
+    [NAT44_CLASSIFY_NEXT_IN2OUT] = "nat44-in2out-worker-handoff",
+    [NAT44_CLASSIFY_NEXT_OUT2IN] = "nat44-out2in-worker-handoff",
+  },
+};
+
+VLIB_NODE_FUNCTION_MULTIARCH (nat44_handoff_classify_node,
+                              nat44_handoff_classify_node_fn);
+
 /**
  * @brief Add/del NAT address to FIB.
  *
@@ -190,7 +358,7 @@ void snat_add_address (snat_main_t *sm, ip4_address_t *addr, u32 vrf_id)
   /* Add external address to FIB */
   pool_foreach (i, sm->interfaces,
   ({
-    if (i->is_inside)
+    if (nat_interface_is_inside(i))
       continue;
 
     snat_add_del_addr_to_fib(addr, 32, i->sw_if_index, 1);
@@ -198,7 +366,7 @@ void snat_add_address (snat_main_t *sm, ip4_address_t *addr, u32 vrf_id)
   }));
   pool_foreach (i, sm->output_feature_interfaces,
   ({
-    if (i->is_inside)
+    if (nat_interface_is_inside(i))
       continue;
 
     snat_add_del_addr_to_fib(addr, 32, i->sw_if_index, 1);
@@ -569,7 +737,7 @@ delete:
   /* Add/delete external address to FIB */
   pool_foreach (interface, sm->interfaces,
   ({
-    if (interface->is_inside)
+    if (nat_interface_is_inside(interface))
       continue;
 
     snat_add_del_addr_to_fib(&e_addr, 32, interface->sw_if_index, is_add);
@@ -577,7 +745,7 @@ delete:
   }));
   pool_foreach (interface, sm->output_feature_interfaces,
   ({
-    if (interface->is_inside)
+    if (nat_interface_is_inside(interface))
       continue;
 
     snat_add_del_addr_to_fib(&e_addr, 32, interface->sw_if_index, is_add);
@@ -930,7 +1098,7 @@ int snat_del_address (snat_main_t *sm, ip4_address_t addr, u8 delete_sm)
   /* Delete external address from FIB */
   pool_foreach (interface, sm->interfaces,
   ({
-    if (interface->is_inside)
+    if (nat_interface_is_inside(interface))
       continue;
 
     snat_add_del_addr_to_fib(&addr, 32, interface->sw_if_index, 0);
@@ -938,7 +1106,7 @@ int snat_del_address (snat_main_t *sm, ip4_address_t addr, u8 delete_sm)
   }));
   pool_foreach (interface, sm->output_feature_interfaces,
   ({
-    if (interface->is_inside)
+    if (nat_interface_is_inside(interface))
       continue;
 
     snat_add_del_addr_to_fib(&addr, 32, interface->sw_if_index, 0);
@@ -952,7 +1120,7 @@ int snat_interface_add_del (u32 sw_if_index, u8 is_inside, int is_del)
 {
   snat_main_t *sm = &snat_main;
   snat_interface_t *i;
-  const char * feature_name;
+  const char * feature_name, *del_feature_name;
   snat_address_t * ap;
   snat_static_mapping_t * m;
   snat_det_map_t * dm;
@@ -969,9 +1137,6 @@ int snat_interface_add_del (u32 sw_if_index, u8 is_inside, int is_del)
         feature_name = is_inside ?  "nat44-in2out" : "nat44-out2in";
     }
 
-  vnet_feature_enable_disable ("ip4-unicast", feature_name, sw_if_index,
-			       !is_del, 0, 0);
-
   if (sm->fq_in2out_index == ~0 && !sm->deterministic && sm->num_workers > 1)
     sm->fq_in2out_index = vlib_frame_queue_main_init (sm->in2out_node_index, 0);
 
@@ -983,9 +1148,63 @@ int snat_interface_add_del (u32 sw_if_index, u8 is_inside, int is_del)
     if (i->sw_if_index == sw_if_index)
       {
         if (is_del)
-          pool_put (sm->interfaces, i);
+          {
+            if (nat_interface_is_inside(i) && nat_interface_is_outside(i))
+              {
+                if (is_inside)
+                  i->flags &= ~NAT_INTERFACE_FLAG_IS_INSIDE;
+                else
+                  i->flags &= ~NAT_INTERFACE_FLAG_IS_OUTSIDE;
+
+                if (sm->num_workers > 1 && !sm->deterministic)
+                  del_feature_name = "nat44-handoff-classify";
+                else if (sm->deterministic)
+                  del_feature_name = "nat44-det-classify";
+                else
+                  del_feature_name = "nat44-classify";
+
+                vnet_feature_enable_disable ("ip4-unicast", del_feature_name,
+                                             sw_if_index, 0, 0, 0);
+                vnet_feature_enable_disable ("ip4-unicast", feature_name,
+                                             sw_if_index, 1, 0, 0);
+              }
+            else
+              {
+                vnet_feature_enable_disable ("ip4-unicast", feature_name,
+                                             sw_if_index, 0, 0, 0);
+                pool_put (sm->interfaces, i);
+              }
+          }
         else
-          return VNET_API_ERROR_VALUE_EXIST;
+          {
+            if ((nat_interface_is_inside(i) && is_inside) ||
+                (nat_interface_is_outside(i) && !is_inside))
+              return 0;
+
+            if (sm->num_workers > 1 && !sm->deterministic)
+              {
+                del_feature_name = !is_inside ?  "nat44-in2out-worker-handoff" :
+                                                 "nat44-out2in-worker-handoff";
+                feature_name = "nat44-handoff-classify";
+              }
+            else if (sm->deterministic)
+              {
+                del_feature_name = !is_inside ?  "nat44-det-in2out" :
+                                                 "nat44-det-out2in";
+                feature_name = "nat44-det-classify";
+              }
+            else
+              {
+                del_feature_name = !is_inside ?  "nat44-in2out" : "nat44-out2in";
+                feature_name = "nat44-classify";
+              }
+
+            vnet_feature_enable_disable ("ip4-unicast", del_feature_name,
+                                         sw_if_index, 0, 0, 0);
+            vnet_feature_enable_disable ("ip4-unicast", feature_name,
+                                         sw_if_index, 1, 0, 0);
+            goto set_flags;
+          }
 
         goto fib;
       }
@@ -996,7 +1215,14 @@ int snat_interface_add_del (u32 sw_if_index, u8 is_inside, int is_del)
 
   pool_get (sm->interfaces, i);
   i->sw_if_index = sw_if_index;
-  i->is_inside = is_inside;
+  i->flags = 0;
+  vnet_feature_enable_disable ("ip4-unicast", feature_name, sw_if_index, 1, 0, 0);
+
+set_flags:
+  if (is_inside)
+    i->flags |= NAT_INTERFACE_FLAG_IS_INSIDE;
+  else
+    i->flags |= NAT_INTERFACE_FLAG_IS_OUTSIDE;
 
   /* Add/delete external addresses to FIB */
 fib:
@@ -1090,7 +1316,11 @@ fq:
 
   pool_get (sm->output_feature_interfaces, i);
   i->sw_if_index = sw_if_index;
-  i->is_inside = is_inside;
+  i->flags = 0;
+  if (is_inside)
+    i->flags |= NAT_INTERFACE_FLAG_IS_INSIDE;
+  else
+    i->flags |= NAT_INTERFACE_FLAG_IS_OUTSIDE;
 
   /* Add/delete external addresses to FIB */
 fib:
@@ -2486,7 +2716,9 @@ show_snat_command_fn (vlib_main_t * vm,
       ({
         vlib_cli_output (vm, "%U %s", format_vnet_sw_interface_name, vnm,
                          vnet_get_sw_interface (vnm, i->sw_if_index),
-                         i->is_inside ? "in" : "out");
+                         (nat_interface_is_inside(i) &&
+                          nat_interface_is_outside(i)) ? "in out" :
+                         (nat_interface_is_inside(i) ? "in" : "out"));
       }));
 
       pool_foreach (i, sm->output_feature_interfaces,
@@ -2494,7 +2726,9 @@ show_snat_command_fn (vlib_main_t * vm,
         vlib_cli_output (vm, "%U output-feature %s",
                          format_vnet_sw_interface_name, vnm,
                          vnet_get_sw_interface (vnm, i->sw_if_index),
-                         i->is_inside ? "in" : "out");
+                         (nat_interface_is_inside(i) &&
+                          nat_interface_is_outside(i)) ? "in out" :
+                         (nat_interface_is_inside(i) ? "in" : "out"));
       }));
 
       if (vec_len (sm->auto_add_sw_if_indices))
diff --git a/src/plugins/nat/nat.h b/src/plugins/nat/nat.h
index e53e924ff03..d4ad72520da 100644
--- a/src/plugins/nat/nat.h
+++ b/src/plugins/nat/nat.h
@@ -129,6 +129,9 @@ typedef enum {
 #define SNAT_SESSION_FLAG_UNKNOWN_PROTO  2
 #define SNAT_SESSION_FLAG_LOAD_BALANCING 4
 
+#define NAT_INTERFACE_FLAG_IS_INSIDE 1
+#define NAT_INTERFACE_FLAG_IS_OUTSIDE 2
+
 typedef CLIB_PACKED(struct {
   snat_session_key_t out2in;    /* 0-15 */
 
@@ -217,7 +220,7 @@ typedef struct {
 
 typedef struct {
   u32 sw_if_index;
-  u8 is_inside;
+  u8 flags;
 } snat_interface_t;
 
 typedef struct {
@@ -414,6 +417,9 @@ typedef struct {
 */
 #define snat_is_unk_proto_session(s) s->flags & SNAT_SESSION_FLAG_UNKNOWN_PROTO
 
+#define nat_interface_is_inside(i) i->flags & NAT_INTERFACE_FLAG_IS_INSIDE
+#define nat_interface_is_outside(i) i->flags & NAT_INTERFACE_FLAG_IS_OUTSIDE
+
 /*
  * Why is this here? Because we don't need to touch this layer to
  * simply reply to an icmp. We need to change id to a unique
diff --git a/src/plugins/nat/nat64.c b/src/plugins/nat/nat64.c
index bfcfa9b3620..952ca8fb11b 100644
--- a/src/plugins/nat/nat64.c
+++ b/src/plugins/nat/nat64.c
@@ -136,7 +136,7 @@ nat64_add_del_pool_addr (ip4_address_t * addr, u32 vrf_id, u8 is_add)
   /* *INDENT-OFF* */
   pool_foreach (interface, nm->interfaces,
   ({
-    if (interface->is_inside)
+    if (nat_interface_is_inside(interface))
       continue;
 
     snat_add_del_addr_to_fib (addr, 32, interface->sw_if_index, is_add);
@@ -170,7 +170,7 @@ nat64_add_del_interface (u32 sw_if_index, u8 is_inside, u8 is_add)
   snat_address_t *ap;
   const char *feature_name, *arc_name;
 
-  /* Check if address already exists */
+  /* Check if interface already exists */
   /* *INDENT-OFF* */
   pool_foreach (i, nm->interfaces,
   ({
@@ -185,19 +185,29 @@ nat64_add_del_interface (u32 sw_if_index, u8 is_inside, u8 is_add)
   if (is_add)
     {
       if (interface)
-	return VNET_API_ERROR_VALUE_EXIST;
+	goto set_flags;
 
       pool_get (nm->interfaces, interface);
       interface->sw_if_index = sw_if_index;
-      interface->is_inside = is_inside;
-
+      interface->flags = 0;
+    set_flags:
+      if (is_inside)
+	interface->flags |= NAT_INTERFACE_FLAG_IS_INSIDE;
+      else
+	interface->flags |= NAT_INTERFACE_FLAG_IS_OUTSIDE;
     }
   else
     {
       if (!interface)
 	return VNET_API_ERROR_NO_SUCH_ENTRY;
 
-      pool_put (nm->interfaces, interface);
+      if ((nat_interface_is_inside (interface)
+	   && nat_interface_is_outside (interface)))
+	interface->flags &=
+	  is_inside ? ~NAT_INTERFACE_FLAG_IS_INSIDE :
+	  ~NAT_INTERFACE_FLAG_IS_OUTSIDE;
+      else
+	pool_put (nm->interfaces, interface);
     }
 
   if (!is_inside)
diff --git a/src/plugins/nat/nat64_cli.c b/src/plugins/nat/nat64_cli.c
index f3645bbbe0b..4128eda5a38 100644
--- a/src/plugins/nat/nat64_cli.c
+++ b/src/plugins/nat/nat64_cli.c
@@ -268,7 +268,9 @@ nat64_cli_interface_walk (snat_interface_t * i, void *ctx)
 
   vlib_cli_output (vm, " %U %s", format_vnet_sw_interface_name, vnm,
 		   vnet_get_sw_interface (vnm, i->sw_if_index),
-		   i->is_inside ? "in" : "out");
+		   (nat_interface_is_inside (i)
+		    && nat_interface_is_outside (i)) ? "in out" :
+		   nat_interface_is_inside (i) ? "in" : "out");
   return 0;
 }
 
diff --git a/src/plugins/nat/nat_api.c b/src/plugins/nat/nat_api.c
index 3bacdfed051..96f69eba186 100644
--- a/src/plugins/nat/nat_api.c
+++ b/src/plugins/nat/nat_api.c
@@ -224,7 +224,7 @@ static void
   memset (rmp, 0, sizeof (*rmp));
   rmp->_vl_msg_id = ntohs (VL_API_SNAT_INTERFACE_DETAILS + sm->msg_id_base);
   rmp->sw_if_index = ntohl (i->sw_if_index);
-  rmp->is_inside = i->is_inside;
+  rmp->is_inside = nat_interface_is_inside (i);
   rmp->context = context;
 
   vl_msg_api_send_shmem (q, (u8 *) & rmp);
@@ -306,7 +306,7 @@ send_snat_interface_output_feature_details (snat_interface_t * i,
     ntohs (VL_API_SNAT_INTERFACE_OUTPUT_FEATURE_DETAILS + sm->msg_id_base);
   rmp->sw_if_index = ntohl (i->sw_if_index);
   rmp->context = context;
-  rmp->is_inside = i->is_inside;
+  rmp->is_inside = nat_interface_is_inside (i);
 
   vl_msg_api_send_shmem (q, (u8 *) & rmp);
 }
@@ -1658,7 +1658,9 @@ send_nat44_interface_details (snat_interface_t * i,
   memset (rmp, 0, sizeof (*rmp));
   rmp->_vl_msg_id = ntohs (VL_API_NAT44_INTERFACE_DETAILS + sm->msg_id_base);
   rmp->sw_if_index = ntohl (i->sw_if_index);
-  rmp->is_inside = i->is_inside;
+  rmp->is_inside = (nat_interface_is_inside (i)
+		    && nat_interface_is_outside (i)) ? 2 :
+    nat_interface_is_inside (i);
   rmp->context = context;
 
   vl_msg_api_send_shmem (q, (u8 *) & rmp);
@@ -1741,7 +1743,7 @@ send_nat44_interface_output_feature_details (snat_interface_t * i,
     ntohs (VL_API_NAT44_INTERFACE_OUTPUT_FEATURE_DETAILS + sm->msg_id_base);
   rmp->sw_if_index = ntohl (i->sw_if_index);
   rmp->context = context;
-  rmp->is_inside = i->is_inside;
+  rmp->is_inside = nat_interface_is_inside (i);
 
   vl_msg_api_send_shmem (q, (u8 *) & rmp);
 }
@@ -2867,7 +2869,9 @@ nat64_api_interface_walk (snat_interface_t * i, void *arg)
   memset (rmp, 0, sizeof (*rmp));
   rmp->_vl_msg_id = ntohs (VL_API_NAT64_INTERFACE_DETAILS + sm->msg_id_base);
   rmp->sw_if_index = ntohl (i->sw_if_index);
-  rmp->is_inside = i->is_inside;
+  rmp->is_inside = (nat_interface_is_inside (i)
+		    && nat_interface_is_outside (i)) ? 2 :
+    nat_interface_is_inside (i);
   rmp->context = ctx->context;
 
   vl_msg_api_send_shmem (ctx->q, (u8 *) & rmp);
diff --git a/src/plugins/nat/nat_det.c b/src/plugins/nat/nat_det.c
index 3af6698c09a..1b00d40b4ae 100644
--- a/src/plugins/nat/nat_det.c
+++ b/src/plugins/nat/nat_det.c
@@ -94,7 +94,7 @@ snat_det_add_map (snat_main_t * sm, ip4_address_t * in_addr, u8 in_plen,
   /* *INDENT-OFF* */
   pool_foreach (i, sm->interfaces,
   ({
-    if (i->is_inside)
+    if (nat_interface_is_inside(i))
       continue;
 
     snat_add_del_addr_to_fib(out_addr, out_plen, i->sw_if_index, is_add);