Add special Twice-NAT feature (VPP-1221)

When enabled then Twice-NAT is applied only when
source IP equals destination IP after DNAT

Change-Id: I58a9d1d222b2a10c83eafffb2107f32c1b4aa3a8
Signed-off-by: Juraj Sloboda <jsloboda@cisco.com>

9 files changed, 226 insertions, 126 deletions

diff --git a/src/plugins/nat/in2out.c b/src/plugins/nat/in2out.c
index 7d9d6c3e6c1..786b6c6887b 100755
--- a/src/plugins/nat/in2out.c
+++ b/src/plugins/nat/in2out.c
@@ -1273,6 +1273,7 @@ create_ses:
 
       s->ext_host_addr.as_u32 = ip->dst_address.as_u32;
       s->flags |= SNAT_SESSION_FLAG_UNKNOWN_PROTO;
+      s->flags |= SNAT_SESSION_FLAG_ENDPOINT_DEPENDENT;
       s->outside_address_index = address_index;
       s->out2in.addr.as_u32 = new_addr;
       s->out2in.fib_index = sm->outside_fib_index;
@@ -1402,6 +1403,7 @@ snat_in2out_lb (snat_main_t *sm,
       s->flags |= SNAT_SESSION_FLAG_STATIC_MAPPING;
       if (lb)
         s->flags |= SNAT_SESSION_FLAG_LOAD_BALANCING;
+      s->flags |= SNAT_SESSION_FLAG_ENDPOINT_DEPENDENT;
       s->outside_address_index = ~0;
       s->in2out = l_key;
       s->out2in = e_key;
diff --git a/src/plugins/nat/nat.api b/src/plugins/nat/nat.api
index 69b6045c4cb..23c89adef7a 100644
--- a/src/plugins/nat/nat.api
+++ b/src/plugins/nat/nat.api
@@ -352,6 +352,9 @@ define nat44_interface_output_feature_details {
     @param vfr_id - VRF ID
     @param twice_nat - if 1 translate external host address and port, only for
                        1:1 NAPT (addr_only must be 0)
+    @param self_twice_nat - if 1 translate external host address and port
+                            whenever external host address equals
+                            local address of internal host
     @param out2in_only - if 1 rule match only out2in direction
     @param tag - opaque string tag
 */
@@ -368,6 +371,7 @@ autoreply define nat44_add_del_static_mapping {
   u32 external_sw_if_index;
   u32 vrf_id;
   u8 twice_nat;
+  u8 self_twice_nat;
   u8 out2in_only;
   u8 tag[64];
 };
@@ -392,6 +396,9 @@ define nat44_static_mapping_dump {
     @param external_sw_if_index - external interface
     @param vfr_id - VRF ID
     @param twice_nat - if 1 translate external host address and port
+    @param self_twice_nat - if 1 translate external host address and port
+                            whenever external host address equals
+                            local address of internal host
     @param out2in_only - if 1 rule match only out2in direction
     @param tag - opaque string tag
 */
@@ -406,6 +413,7 @@ define nat44_static_mapping_details {
   u32 external_sw_if_index;
   u32 vrf_id;
   u8 twice_nat;
+  u8 self_twice_nat;
   u8 out2in_only;
   u8 tag[64];
 };
@@ -584,6 +592,9 @@ typeonly manual_endian define nat44_lb_addr_port {
     @param protocol - IP protocol number of the service
     @param vrf_id - internal network VRF ID
     @param twice_nat - if 1 translate external host address and port
+    @param self_twice_nat - if 1 translate external host address and port
+                            whenever external host address equals
+                            local address of internal host
     @param out2in_only - if 1 rule match only out2in direction
     @param tag - opaque string tag
     @param local_num - number of local network nodes
@@ -598,6 +609,7 @@ autoreply manual_endian define nat44_add_del_lb_static_mapping {
   u8 protocol;
   u32 vrf_id;
   u8 twice_nat;
+  u8 self_twice_nat;
   u8 out2in_only;
   u8 tag[64];
   u8 local_num;
@@ -621,6 +633,9 @@ define nat44_lb_static_mapping_dump {
     @param protocol - IP protocol number of the service
     @param vrf_id - internal network VRF ID
     @param twice_nat - if 1 translate external host address and port
+    @param self_twice_nat - if 1 translate external host address and port
+                            whenever external host address equals
+                            local address of internal host
     @param out2in_only - if 1 rule match only out2in direction
     @param tag - opaque string tag
     @param local_num - number of local network nodes
@@ -633,6 +648,7 @@ manual_endian define nat44_lb_static_mapping_details {
   u8 protocol;
   u32 vrf_id;
   u8 twice_nat;
+  u8 self_twice_nat;
   u8 out2in_only;
   u8 tag[64];
   u8 local_num;
diff --git a/src/plugins/nat/nat.c b/src/plugins/nat/nat.c
index 51fbb1336e1..499f3a242cb 100755
--- a/src/plugins/nat/nat.c
+++ b/src/plugins/nat/nat.c
@@ -669,7 +669,11 @@ snat_add_static_mapping_when_resolved (snat_main_t * sm,
  * @param addr_only If 0 address port and pair mapping, otherwise address only.
  * @param sw_if_index External port instead of specific IP address.
  * @param is_add If 0 delete static mapping, otherwise add.
- * @param twice_nat If 1 translate external host address and port.
+ * @param twice_nat If value is TWICE_NAT then translate external host address
+ *                  and port.
+ *                  If value is TWICE_NAT_SELF then translate external host
+ *                  address and port whenever external host address equals
+ *                  local address of internal host.
  * @param out2in_only If 1 rule match only out2in direction
  * @param tag - opaque string tag
  *
@@ -678,7 +682,8 @@ snat_add_static_mapping_when_resolved (snat_main_t * sm,
 int snat_add_static_mapping(ip4_address_t l_addr, ip4_address_t e_addr,
                             u16 l_port, u16 e_port, u32 vrf_id, int addr_only,
                             u32 sw_if_index, snat_protocol_t proto, int is_add,
-                            u8 twice_nat, u8 out2in_only, u8 * tag)
+                            twice_nat_type_t twice_nat, u8 out2in_only,
+                            u8 * tag)
 {
   snat_main_t * sm = &snat_main;
   snat_static_mapping_t *m;
@@ -1159,7 +1164,8 @@ static int lb_local_exists (nat44_lb_addr_port_t * local,
 int nat44_add_del_lb_static_mapping (ip4_address_t e_addr, u16 e_port,
                                      snat_protocol_t proto, u32 vrf_id,
                                      nat44_lb_addr_port_t *locals, u8 is_add,
-                                     u8 twice_nat, u8 out2in_only, u8 *tag)
+                                     twice_nat_type_t twice_nat, u8 out2in_only,
+                                     u8 *tag)
 {
   snat_main_t * sm = &snat_main;
   snat_static_mapping_t *m;
@@ -1993,7 +1999,7 @@ int snat_static_mapping_match (snat_main_t * sm,
                                snat_session_key_t * mapping,
                                u8 by_external,
                                u8 *is_addr_only,
-                               u8 *twice_nat,
+                               twice_nat_type_t *twice_nat,
                                u8 *lb)
 {
   clib_bihash_kv_8_8_t kv, value;
@@ -2741,7 +2747,9 @@ u8 * format_snat_static_mapping (u8 * s, va_list * args)
       s = format (s, "local %U external %U vrf %d %s",
                   format_ip4_address, &m->local_addr,
                   format_ip4_address, &m->external_addr,
-                  m->vrf_id, m->twice_nat ? "twice-nat" : "");
+                  m->vrf_id,
+                  m->twice_nat == TWICE_NAT ? "twice-nat" :
+                  m->twice_nat == TWICE_NAT_SELF ? "self-twice-nat" : "");
   else
    {
       if (vec_len (m->locals))
@@ -2750,7 +2758,8 @@ u8 * format_snat_static_mapping (u8 * s, va_list * args)
                       format_snat_protocol, m->proto,
                       m->vrf_id,
                       format_ip4_address, &m->external_addr, m->external_port,
-                      m->twice_nat ? "twice-nat" : "",
+                      m->twice_nat == TWICE_NAT ? "twice-nat" :
+                      m->twice_nat == TWICE_NAT_SELF ? "self-twice-nat" : "",
                       m->out2in_only ? "out2in-only" : "");
           vec_foreach (local, m->locals)
             s = format (s, "\n  local %U:%d probability %d\%",
@@ -2762,7 +2771,9 @@ u8 * format_snat_static_mapping (u8 * s, va_list * args)
                     format_snat_protocol, m->proto,
                     format_ip4_address, &m->local_addr, m->local_port,
                     format_ip4_address, &m->external_addr, m->external_port,
-                    m->vrf_id, m->twice_nat ? "twice-nat" : "",
+                    m->vrf_id,
+                    m->twice_nat == TWICE_NAT ? "twice-nat" :
+                    m->twice_nat == TWICE_NAT_SELF ? "self-twice-nat" : "",
                     m->out2in_only ? "out2in-only" : "");
    }
   return s;
diff --git a/src/plugins/nat/nat.h b/src/plugins/nat/nat.h
index 8d7d1738fb3..775376fcbab 100644
--- a/src/plugins/nat/nat.h
+++ b/src/plugins/nat/nat.h
@@ -125,11 +125,12 @@ typedef enum {
 } snat_session_state_t;
 
 
-#define SNAT_SESSION_FLAG_STATIC_MAPPING 1
-#define SNAT_SESSION_FLAG_UNKNOWN_PROTO  2
-#define SNAT_SESSION_FLAG_LOAD_BALANCING 4
-#define SNAT_SESSION_FLAG_TWICE_NAT      8
-#define SNAT_SESSION_FLAG_FWD_BYPASS     16
+#define SNAT_SESSION_FLAG_STATIC_MAPPING       1
+#define SNAT_SESSION_FLAG_UNKNOWN_PROTO        2
+#define SNAT_SESSION_FLAG_LOAD_BALANCING       4
+#define SNAT_SESSION_FLAG_TWICE_NAT            8
+#define SNAT_SESSION_FLAG_ENDPOINT_DEPENDENT   16
+#define SNAT_SESSION_FLAG_FWD_BYPASS           32
 
 #define NAT_INTERFACE_FLAG_IS_INSIDE 1
 #define NAT_INTERFACE_FLAG_IS_OUTSIDE 2
@@ -211,13 +212,19 @@ typedef struct {
   u8 prefix;
 } nat44_lb_addr_port_t;
 
+typedef enum {
+  TWICE_NAT_DISABLED,
+  TWICE_NAT,
+  TWICE_NAT_SELF,
+} twice_nat_type_t;
+
 typedef struct {
   ip4_address_t local_addr;
   ip4_address_t external_addr;
   u16 local_port;
   u16 external_port;
   u8 addr_only;
-  u8 twice_nat;
+  twice_nat_type_t twice_nat;
   u8 out2in_only;
   u32 vrf_id;
   u32 fib_index;
@@ -422,7 +429,7 @@ int snat_static_mapping_match (snat_main_t * sm,
                                snat_session_key_t * mapping,
                                u8 by_external,
                                u8 *is_addr_only,
-                               u8 *twice_nat,
+                               twice_nat_type_t *twice_nat,
                                u8 *lb);
 
 void snat_add_del_addr_to_fib (ip4_address_t * addr,
@@ -474,7 +481,7 @@ typedef struct {
     @param s NAT session
     @return 1 if NAT session is endpoint dependent
 */
-#define is_ed_session(s) (snat_is_unk_proto_session (s) || is_twice_nat_session (s) || is_lb_session (s))
+#define is_ed_session(s) (s->flags & SNAT_SESSION_FLAG_ENDPOINT_DEPENDENT)
 
 #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
@@ -558,7 +565,8 @@ void nat44_add_del_address_dpo (ip4_address_t addr, u8 is_add);
 int snat_add_static_mapping(ip4_address_t l_addr, ip4_address_t e_addr,
                             u16 l_port, u16 e_port, u32 vrf_id, int addr_only,
                             u32 sw_if_index, snat_protocol_t proto, int is_add,
-                            u8 twice_nat, u8 out2in_only, u8 *tag);
+                            twice_nat_type_t twice_nat, u8 out2in_only,
+                            u8 *tag);
 clib_error_t * snat_api_init(vlib_main_t * vm, snat_main_t * sm);
 int snat_set_workers (uword * bitmap);
 int snat_interface_add_del(u32 sw_if_index, u8 is_inside, int is_del);
@@ -571,7 +579,8 @@ u8 * format_snat_protocol(u8 * s, va_list * args);
 int nat44_add_del_lb_static_mapping (ip4_address_t e_addr, u16 e_port,
                                      snat_protocol_t proto, u32 vrf_id,
                                      nat44_lb_addr_port_t *locals, u8 is_add,
-                                     u8 twice_nat, u8 out2in_only, u8 *tag);
+                                     twice_nat_type_t twice_nat, u8 out2in_only,
+                                     u8 *tag);
 int nat44_del_session (snat_main_t *sm, ip4_address_t *addr, u16 port,
                        snat_protocol_t proto, u32 vrf_id, int is_in);
 void nat_free_session_data (snat_main_t * sm, snat_session_t * s,
diff --git a/src/plugins/nat/nat44_cli.c b/src/plugins/nat/nat44_cli.c
index da97a801b7f..2f1e9a019ac 100644
--- a/src/plugins/nat/nat44_cli.c
+++ b/src/plugins/nat/nat44_cli.c
@@ -501,7 +501,7 @@ add_static_mapping_command_fn (vlib_main_t * vm,
   int rv;
   snat_protocol_t proto = ~0;
   u8 proto_set = 0;
-  u8 twice_nat = 0;
+  twice_nat_type_t twice_nat = TWICE_NAT_DISABLED;
   u8 out2in_only = 0;
 
   if (sm->deterministic)
@@ -538,7 +538,9 @@ add_static_mapping_command_fn (vlib_main_t * vm,
       else if (unformat (line_input, "%U", unformat_snat_protocol, &proto))
 	proto_set = 1;
       else if (unformat (line_input, "twice-nat"))
-	twice_nat = 1;
+	twice_nat = TWICE_NAT;
+      else if (unformat (line_input, "self-twice-nat"))
+	twice_nat = TWICE_NAT_SELF;
       else if (unformat (line_input, "out2in-only"))
 	out2in_only = 1;
       else if (unformat (line_input, "del"))
@@ -688,7 +690,7 @@ add_lb_static_mapping_command_fn (vlib_main_t * vm,
   snat_protocol_t proto;
   u8 proto_set = 0;
   nat44_lb_addr_port_t *locals = 0, local;
-  u8 twice_nat = 0;
+  twice_nat_type_t twice_nat = TWICE_NAT_DISABLED;
   u8 out2in_only = 0;
 
   if (sm->deterministic)
@@ -718,7 +720,9 @@ add_lb_static_mapping_command_fn (vlib_main_t * vm,
 			 &proto))
 	proto_set = 1;
       else if (unformat (line_input, "twice-nat"))
-	twice_nat = 1;
+	twice_nat = TWICE_NAT;
+      else if (unformat (line_input, "self-twice-nat"))
+	twice_nat = TWICE_NAT_SELF;
       else if (unformat (line_input, "out2in-only"))
 	out2in_only = 1;
       else if (unformat (line_input, "del"))
@@ -1584,7 +1588,8 @@ VLIB_CLI_COMMAND (add_static_mapping_command, static) = {
   .function = add_static_mapping_command_fn,
   .short_help =
     "nat44 add static mapping tcp|udp|icmp local <addr> [<port>] "
-    "external <addr> [<port>] [vrf <table-id>] [twice-nat] [out2in-only] [del]",
+    "external <addr> [<port>] [vrf <table-id>] [twice-nat|self-twice-nat] "
+    "[out2in-only] [del]",
 };
 
 /*?
@@ -1622,8 +1627,8 @@ VLIB_CLI_COMMAND (add_lb_static_mapping_command, static) = {
   .function = add_lb_static_mapping_command_fn,
   .short_help =
     "nat44 add load-balancing static mapping protocol tcp|udp "
-    "external <addr>:<port> local <addr>:<port> probability <n> [twice-nat] "
-    "[vrf <table-id>] [out2in-only] [del]",
+    "external <addr>:<port> local <addr>:<port> probability <n> "
+    "[twice-nat|self-twice-nat] [vrf <table-id>] [out2in-only] [del]",
 };
 
 /*?
diff --git a/src/plugins/nat/nat_api.c b/src/plugins/nat/nat_api.c
index 56b261d1bb9..417d2984011 100644
--- a/src/plugins/nat/nat_api.c
+++ b/src/plugins/nat/nat_api.c
@@ -724,6 +724,7 @@ static void
   ip4_address_t local_addr, external_addr;
   u16 local_port = 0, external_port = 0;
   u32 vrf_id, external_sw_if_index;
+  twice_nat_type_t twice_nat = TWICE_NAT_DISABLED;
   int rv = 0;
   snat_protocol_t proto;
   u8 *tag = 0;
@@ -744,6 +745,10 @@ static void
   vrf_id = clib_net_to_host_u32 (mp->vrf_id);
   external_sw_if_index = clib_net_to_host_u32 (mp->external_sw_if_index);
   proto = ip_proto_to_snat_proto (mp->protocol);
+  if (mp->twice_nat)
+    twice_nat = TWICE_NAT;
+  else if (mp->self_twice_nat)
+    twice_nat = TWICE_NAT_SELF;
   mp->tag[sizeof (mp->tag) - 1] = 0;
   tag = format (0, "%s", mp->tag);
   vec_terminate_c_string (tag);
@@ -751,7 +756,7 @@ static void
   rv = snat_add_static_mapping (local_addr, external_addr, local_port,
 				external_port, vrf_id, mp->addr_only,
 				external_sw_if_index, proto, mp->is_add,
-				mp->twice_nat, mp->out2in_only, tag);
+				twice_nat, mp->out2in_only, tag);
 
   vec_free (tag);
 
@@ -804,7 +809,10 @@ send_nat44_static_mapping_details (snat_static_mapping_t * m,
   rmp->external_sw_if_index = ~0;
   rmp->vrf_id = htonl (m->vrf_id);
   rmp->context = context;
-  rmp->twice_nat = m->twice_nat;
+  if (m->twice_nat == TWICE_NAT)
+    rmp->twice_nat = 1;
+  else if (m->twice_nat == TWICE_NAT_SELF)
+    rmp->self_twice_nat = 1;
   rmp->out2in_only = m->out2in_only;
   if (m->addr_only == 0)
     {
@@ -1324,6 +1332,7 @@ static void
 {
   snat_main_t *sm = &snat_main;
   vl_api_nat44_add_del_lb_static_mapping_reply_t *rmp;
+  twice_nat_type_t twice_nat = TWICE_NAT_DISABLED;
   int rv = 0;
   nat44_lb_addr_port_t *locals = 0;
   ip4_address_t e_addr;
@@ -1339,6 +1348,10 @@ static void
   locals = unformat_nat44_lb_addr_port (mp->locals, mp->local_num);
   clib_memcpy (&e_addr, mp->external_addr, 4);
   proto = ip_proto_to_snat_proto (mp->protocol);
+  if (mp->twice_nat)
+    twice_nat = TWICE_NAT;
+  else if (mp->self_twice_nat)
+    twice_nat = TWICE_NAT_SELF;
   mp->tag[sizeof (mp->tag) - 1] = 0;
   tag = format (0, "%s", mp->tag);
   vec_terminate_c_string (tag);
@@ -1347,7 +1360,7 @@ static void
     nat44_add_del_lb_static_mapping (e_addr,
 				     clib_net_to_host_u16 (mp->external_port),
 				     proto, clib_net_to_host_u32 (mp->vrf_id),
-				     locals, mp->is_add, mp->twice_nat,
+				     locals, mp->is_add, twice_nat,
 				     mp->out2in_only, tag);
 
   vec_free (locals);
@@ -1391,7 +1404,10 @@ send_nat44_lb_static_mapping_details (snat_static_mapping_t * m,
   rmp->protocol = snat_proto_to_ip_proto (m->proto);
   rmp->vrf_id = ntohl (m->vrf_id);
   rmp->context = context;
-  rmp->twice_nat = m->twice_nat;
+  if (m->twice_nat == TWICE_NAT)
+    rmp->twice_nat = 1;
+  else if (m->twice_nat == TWICE_NAT_SELF)
+    rmp->self_twice_nat = 1;
   rmp->out2in_only = m->out2in_only;
   if (m->tag)
     strncpy ((char *) rmp->tag, (char *) m->tag, vec_len (m->tag));
diff --git a/src/plugins/nat/out2in.c b/src/plugins/nat/out2in.c
index 637a07341e0..a0128b8d61d 100755
--- a/src/plugins/nat/out2in.c
+++ b/src/plugins/nat/out2in.c
@@ -871,6 +871,7 @@ snat_out2in_unknown_proto (snat_main_t *sm,
       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->flags |= SNAT_SESSION_FLAG_ENDPOINT_DEPENDENT;
       s->outside_address_index = ~0;
       s->out2in.addr.as_u32 = old_addr;
       s->out2in.fib_index = rx_fib_index;
@@ -935,7 +936,8 @@ snat_out2in_lb (snat_main_t *sm,
   snat_user_t *u;
   u32 address_index;
   snat_session_key_t eh_key;
-  u8 twice_nat, lb;
+  twice_nat_type_t twice_nat;
+  u8 lb;
 
   old_addr = ip->dst_address.as_u32;
 
@@ -987,6 +989,7 @@ snat_out2in_lb (snat_main_t *sm,
       s->flags |= SNAT_SESSION_FLAG_STATIC_MAPPING;
       if (lb)
         s->flags |= SNAT_SESSION_FLAG_LOAD_BALANCING;
+      s->flags |= SNAT_SESSION_FLAG_ENDPOINT_DEPENDENT;
       s->outside_address_index = ~0;
       s->out2in = e_key;
       s->in2out = l_key;
@@ -997,7 +1000,9 @@ snat_out2in_lb (snat_main_t *sm,
       if (clib_bihash_add_del_16_8 (&sm->out2in_ed, &s_kv, 1))
         clib_warning ("out2in-ed key add failed");
 
-      if (twice_nat)
+      if (twice_nat == TWICE_NAT ||
+          (twice_nat == TWICE_NAT_SELF &&
+           ip->src_address.as_u32 == l_key.addr.as_u32))
         {
           eh_key.protocol = proto;
           if (snat_alloc_outside_address_and_port (sm->twice_nat_addresses, 0,
diff --git a/test/test_nat.py b/test/test_nat.py
index 7c126199072..47f3b8c7299 100644
--- a/test/test_nat.py
+++ b/test/test_nat.py
@@ -922,6 +922,9 @@ class TestNAT44(MethodHolder):
             cls.pg0.generate_remote_hosts(3)
             cls.pg0.configure_ipv4_neighbors()
 
+            cls.pg1.generate_remote_hosts(1)
+            cls.pg1.configure_ipv4_neighbors()
+
             cls.overlapping_interfaces = list(list(cls.pg_interfaces[4:7]))
             cls.vapi.ip_table_add_del(10, is_add=1)
             cls.vapi.ip_table_add_del(20, is_add=1)
@@ -1029,6 +1032,7 @@ class TestNAT44(MethodHolder):
                 vrf_id=sm.vrf_id,
                 protocol=sm.protocol,
                 twice_nat=sm.twice_nat,
+                self_twice_nat=sm.self_twice_nat,
                 out2in_only=sm.out2in_only,
                 tag=sm.tag,
                 external_sw_if_index=sm.external_sw_if_index,
@@ -1042,6 +1046,7 @@ class TestNAT44(MethodHolder):
                 lb_sm.protocol,
                 vrf_id=lb_sm.vrf_id,
                 twice_nat=lb_sm.twice_nat,
+                self_twice_nat=lb_sm.self_twice_nat,
                 out2in_only=lb_sm.out2in_only,
                 tag=lb_sm.tag,
                 is_add=0,
@@ -1072,7 +1077,8 @@ class TestNAT44(MethodHolder):
     def nat44_add_static_mapping(self, local_ip, external_ip='0.0.0.0',
                                  local_port=0, external_port=0, vrf_id=0,
                                  is_add=1, external_sw_if_index=0xFFFFFFFF,
-                                 proto=0, twice_nat=0, out2in_only=0, tag=""):
+                                 proto=0, twice_nat=0, self_twice_nat=0,
+                                 out2in_only=0, tag=""):
         """
         Add/delete NAT44 static mapping
 
@@ -1085,6 +1091,9 @@ class TestNAT44(MethodHolder):
         :param external_sw_if_index: External interface instead of IP address
         :param proto: IP protocol (Mandatory if port specified)
         :param twice_nat: 1 if translate external host address and port
+        :param self_twice_nat: 1 if translate external host address and port
+                               whenever external host address equals
+                               local address of internal host
         :param out2in_only: if 1 rule is matching only out2in direction
         :param tag: Opaque string tag
         """
@@ -1103,6 +1112,7 @@ class TestNAT44(MethodHolder):
             vrf_id,
             proto,
             twice_nat,
+            self_twice_nat,
             out2in_only,
             tag,
             is_add)
@@ -3844,56 +3854,128 @@ class TestNAT44(MethodHolder):
             self.logger.error(ppp("Unexpected or invalid packet:", p))
             raise
 
-    def test_twice_nat(self):
-        """ Twice NAT44 """
+    def twice_nat_common(self, self_twice_nat=False, same_pg=False, lb=False,
+                         client_id=None):
         twice_nat_addr = '10.0.1.3'
+
         port_in = 8080
+        if lb:
+            if not same_pg:
+                port_in1 = port_in
+                port_in2 = port_in
+            else:
+                port_in1 = port_in+1
+                port_in2 = port_in+2
+
         port_out = 80
         eh_port_out = 4567
-        eh_port_in = 0
+
+        server1 = self.pg0.remote_hosts[0]
+        server2 = self.pg0.remote_hosts[1]
+        if lb and same_pg:
+            server2 = server1
+        if not lb:
+            server = server1
+
+        pg0 = self.pg0
+        if same_pg:
+            pg1 = self.pg0
+        else:
+            pg1 = self.pg1
+
+        eh_translate = ((not self_twice_nat) or (not lb and same_pg) or
+                        client_id == 1)
+
         self.nat44_add_address(self.nat_addr)
         self.nat44_add_address(twice_nat_addr, twice_nat=1)
-        self.nat44_add_static_mapping(self.pg0.remote_ip4, self.nat_addr,
-                                      port_in, port_out, proto=IP_PROTOS.tcp,
-                                      twice_nat=1)
-        self.vapi.nat44_interface_add_del_feature(self.pg0.sw_if_index)
-        self.vapi.nat44_interface_add_del_feature(self.pg1.sw_if_index,
+        if not lb:
+            self.nat44_add_static_mapping(pg0.remote_ip4, self.nat_addr,
+                                          port_in, port_out,
+                                          proto=IP_PROTOS.tcp,
+                                          twice_nat=int(not self_twice_nat),
+                                          self_twice_nat=int(self_twice_nat))
+        else:
+            locals = [{'addr': server1.ip4n,
+                       'port': port_in1,
+                       'probability': 50},
+                      {'addr': server2.ip4n,
+                       'port': port_in2,
+                       'probability': 50}]
+            out_addr_n = socket.inet_pton(socket.AF_INET, self.nat_addr)
+            self.vapi.nat44_add_del_lb_static_mapping(out_addr_n,
+                                                      port_out,
+                                                      IP_PROTOS.tcp,
+                                                      twice_nat=int(
+                                                          not self_twice_nat),
+                                                      self_twice_nat=int(
+                                                          self_twice_nat),
+                                                      local_num=len(locals),
+                                                      locals=locals)
+        self.vapi.nat44_interface_add_del_feature(pg0.sw_if_index)
+        self.vapi.nat44_interface_add_del_feature(pg1.sw_if_index,
                                                   is_inside=0)
 
-        p = (Ether(src=self.pg1.remote_mac, dst=self.pg1.local_mac) /
-             IP(src=self.pg1.remote_ip4, dst=self.nat_addr) /
+        if same_pg:
+            if not lb:
+                client = server
+            else:
+                assert client_id is not None
+                if client_id == 1:
+                    client = self.pg0.remote_hosts[0]
+                elif client_id == 2:
+                    client = self.pg0.remote_hosts[1]
+        else:
+            client = pg1.remote_hosts[0]
+        p = (Ether(src=pg1.remote_mac, dst=pg1.local_mac) /
+             IP(src=client.ip4, dst=self.nat_addr) /
              TCP(sport=eh_port_out, dport=port_out))
-        self.pg1.add_stream(p)
+        pg1.add_stream(p)
         self.pg_enable_capture(self.pg_interfaces)
         self.pg_start()
-        capture = self.pg0.get_capture(1)
+        capture = pg0.get_capture(1)
         p = capture[0]
         try:
             ip = p[IP]
             tcp = p[TCP]
-            self.assertEqual(ip.dst, self.pg0.remote_ip4)
-            self.assertEqual(ip.src, twice_nat_addr)
-            self.assertEqual(tcp.dport, port_in)
-            self.assertNotEqual(tcp.sport, eh_port_out)
+            if lb:
+                if ip.dst == server1.ip4:
+                    server = server1
+                    port_in = port_in1
+                else:
+                    server = server2
+                    port_in = port_in2
+            self.assertEqual(ip.dst, server.ip4)
+            if lb and same_pg:
+                self.assertIn(tcp.dport, [port_in1, port_in2])
+            else:
+                self.assertEqual(tcp.dport, port_in)
+            if eh_translate:
+                self.assertEqual(ip.src, twice_nat_addr)
+                self.assertNotEqual(tcp.sport, eh_port_out)
+            else:
+                self.assertEqual(ip.src, client.ip4)
+                self.assertEqual(tcp.sport, eh_port_out)
+            eh_addr_in = ip.src
             eh_port_in = tcp.sport
+            saved_port_in = tcp.dport
             self.check_tcp_checksum(p)
             self.check_ip_checksum(p)
         except:
             self.logger.error(ppp("Unexpected or invalid packet:", p))
             raise
 
-        p = (Ether(src=self.pg0.remote_mac, dst=self.pg0.local_mac) /
-             IP(src=self.pg0.remote_ip4, dst=twice_nat_addr) /
-             TCP(sport=port_in, dport=eh_port_in))
-        self.pg0.add_stream(p)
+        p = (Ether(src=server.mac, dst=pg0.local_mac) /
+             IP(src=server.ip4, dst=eh_addr_in) /
+             TCP(sport=saved_port_in, dport=eh_port_in))
+        pg0.add_stream(p)
         self.pg_enable_capture(self.pg_interfaces)
         self.pg_start()
-        capture = self.pg1.get_capture(1)
+        capture = pg1.get_capture(1)
         p = capture[0]
         try:
             ip = p[IP]
             tcp = p[TCP]
-            self.assertEqual(ip.dst, self.pg1.remote_ip4)
+            self.assertEqual(ip.dst, client.ip4)
             self.assertEqual(ip.src, self.nat_addr)
             self.assertEqual(tcp.dport, eh_port_out)
             self.assertEqual(tcp.sport, port_out)
@@ -3903,84 +3985,31 @@ class TestNAT44(MethodHolder):
             self.logger.error(ppp("Unexpected or invalid packet:", p))
             raise
 
-    def test_twice_nat_lb(self):
-        """ Twice NAT44 local service load balancing """
-        external_addr_n = socket.inet_pton(socket.AF_INET, self.nat_addr)
-        twice_nat_addr = '10.0.1.3'
-        local_port = 8080
-        external_port = 80
-        eh_port_out = 4567
-        eh_port_in = 0
-        server1 = self.pg0.remote_hosts[0]
-        server2 = self.pg0.remote_hosts[1]
+    def test_twice_nat(self):
+        """ Twice NAT44 """
+        self.twice_nat_common()
 
-        locals = [{'addr': server1.ip4n,
-                   'port': local_port,
-                   'probability': 50},
-                  {'addr': server2.ip4n,
-                   'port': local_port,
-                   'probability': 50}]
+    def test_self_twice_nat_positive(self):
+        """ Self Twice NAT44 (positive test) """
+        self.twice_nat_common(self_twice_nat=True, same_pg=True)
 
-        self.nat44_add_address(self.nat_addr)
-        self.nat44_add_address(twice_nat_addr, twice_nat=1)
+    def test_self_twice_nat_negative(self):
+        """ Self Twice NAT44 (negative test) """
+        self.twice_nat_common(self_twice_nat=True)
 
-        self.vapi.nat44_add_del_lb_static_mapping(external_addr_n,
-                                                  external_port,
-                                                  IP_PROTOS.tcp,
-                                                  twice_nat=1,
-                                                  local_num=len(locals),
-                                                  locals=locals)
-        self.vapi.nat44_interface_add_del_feature(self.pg0.sw_if_index)
-        self.vapi.nat44_interface_add_del_feature(self.pg1.sw_if_index,
-                                                  is_inside=0)
+    def test_twice_nat_lb(self):
+        """ Twice NAT44 local service load balancing """
+        self.twice_nat_common(lb=True)
 
-        p = (Ether(src=self.pg1.remote_mac, dst=self.pg1.local_mac) /
-             IP(src=self.pg1.remote_ip4, dst=self.nat_addr) /
-             TCP(sport=eh_port_out, dport=external_port))
-        self.pg1.add_stream(p)
-        self.pg_enable_capture(self.pg_interfaces)
-        self.pg_start()
-        capture = self.pg0.get_capture(1)
-        p = capture[0]
-        server = None
-        try:
-            ip = p[IP]
-            tcp = p[TCP]
-            self.assertEqual(ip.src, twice_nat_addr)
-            self.assertIn(ip.dst, [server1.ip4, server2.ip4])
-            if ip.dst == server1.ip4:
-                server = server1
-            else:
-                server = server2
-            self.assertNotEqual(tcp.sport, eh_port_out)
-            eh_port_in = tcp.sport
-            self.assertEqual(tcp.dport, local_port)
-            self.check_tcp_checksum(p)
-            self.check_ip_checksum(p)
-        except:
-            self.logger.error(ppp("Unexpected or invalid packet:", p))
-            raise
+    def test_self_twice_nat_lb_positive(self):
+        """ Self Twice NAT44 local service load balancing (positive test) """
+        self.twice_nat_common(lb=True, self_twice_nat=True, same_pg=True,
+                              client_id=1)
 
-        p = (Ether(src=server.mac, dst=self.pg0.local_mac) /
-             IP(src=server.ip4, dst=twice_nat_addr) /
-             TCP(sport=local_port, dport=eh_port_in))
-        self.pg0.add_stream(p)
-        self.pg_enable_capture(self.pg_interfaces)
-        self.pg_start()
-        capture = self.pg1.get_capture(1)
-        p = capture[0]
-        try:
-            ip = p[IP]
-            tcp = p[TCP]
-            self.assertEqual(ip.src, self.nat_addr)
-            self.assertEqual(ip.dst, self.pg1.remote_ip4)
-            self.assertEqual(tcp.sport, external_port)
-            self.assertEqual(tcp.dport, eh_port_out)
-            self.check_tcp_checksum(p)
-            self.check_ip_checksum(p)
-        except:
-            self.logger.error(ppp("Unexpected or invalid packet:", p))
-            raise
+    def test_self_twice_nat_lb_negative(self):
+        """ Self Twice NAT44 local service load balancing (negative test) """
+        self.twice_nat_common(lb=True, self_twice_nat=True, same_pg=True,
+                              client_id=2)
 
     def test_twice_nat_interface_addr(self):
         """ Acquire twice NAT44 addresses from interface """
diff --git a/test/vpp_papi_provider.py b/test/vpp_papi_provider.py
index 44cb7b6fc68..53be992aeeb 100644
--- a/test/vpp_papi_provider.py
+++ b/test/vpp_papi_provider.py
@@ -1302,6 +1302,7 @@ class VppPapiProvider(object):
             vrf_id=0,
             protocol=0,
             twice_nat=0,
+            self_twice_nat=0,
             out2in_only=0,
             tag="",
             is_add=1):
@@ -1316,6 +1317,9 @@ class VppPapiProvider(object):
         :param vrf_id: VRF ID
         :param protocol: IP protocol (Default value = 0)
         :param twice_nat: 1 if translate external host address and port
+        :param self_twice_nat: 1 if translate external host address and port
+                               whenever external host address equals
+                               local address of internal host
         :param out2in_only: if 1 rule is matching only out2in direction
         :param tag: Opaque string tag
         :param is_add: 1 if add, 0 if delete (Default value = 1)
@@ -1332,6 +1336,7 @@ class VppPapiProvider(object):
              'vrf_id': vrf_id,
              'protocol': protocol,
              'twice_nat': twice_nat,
+             'self_twice_nat': self_twice_nat,
              'out2in_only': out2in_only,
              'tag': tag})
 
@@ -1496,6 +1501,7 @@ class VppPapiProvider(object):
             protocol,
             vrf_id=0,
             twice_nat=0,
+            self_twice_nat=0,
             out2in_only=0,
             tag='',
             local_num=0,
@@ -1515,6 +1521,7 @@ class VppPapiProvider(object):
              'protocol': protocol,
              'vrf_id': vrf_id,
              'twice_nat': twice_nat,
+             'self_twice_nat': self_twice_nat,
              'out2in_only': out2in_only,
              'tag': tag,
              'local_num': local_num,