snat: Hairpinning (VPP-444)

Change-Id: I73881ef32d547852da96e77402a1758f37e812d5
Signed-off-by: Matus Fabian <matfabia@cisco.com>

2 files changed, 181 insertions, 0 deletions

diff --git a/plugins/snat-plugin/snat/in2out.c b/plugins/snat-plugin/snat/in2out.c
index 43ee2d0e..d7b647ef 100644
--- a/plugins/snat-plugin/snat/in2out.c
+++ b/plugins/snat-plugin/snat/in2out.c
@@ -405,6 +405,108 @@ static inline u32 icmp_in2out_slow_path (snat_main_t *sm,
   return next0;
 }
 
+/**
+ * @brief Hairpinning
+ *
+ * Hairpinning allows two endpoints on the internal side of the NAT to
+ * communicate even if they only use each other's external IP addresses
+ * and ports.
+ *
+ * @param sm     SNAT main.
+ * @param b0     Vlib buffer.
+ * @param ip0    IP header.
+ * @param udp0   UDP header.
+ * @param tcp0   TCP header.
+ * @param proto0 SNAT protocol.
+ */
+static inline void
+snat_hairpinning (snat_main_t *sm,
+                  vlib_buffer_t * b0,
+                  ip4_header_t * ip0,
+                  udp_header_t * udp0,
+                  tcp_header_t * tcp0,
+                  u32 proto0)
+{
+  snat_session_key_t key0, sm0;
+  snat_static_mapping_key_t k0;
+  snat_session_t * s0;
+  clib_bihash_kv_8_8_t kv0, value0;
+  ip_csum_t sum0;
+  u32 new_dst_addr0 = 0, old_dst_addr0, ti = 0, si;
+  u16 new_dst_port0, old_dst_port0;
+
+  key0.addr = ip0->dst_address;
+  key0.port = udp0->dst_port;
+  key0.protocol = proto0;
+  key0.fib_index = sm->outside_fib_index;
+  kv0.key = key0.as_u64;
+
+  /* Check if destination is in active sessions */
+  if (clib_bihash_search_8_8 (&sm->out2in, &kv0, &value0))
+    {
+      /* or static mappings */
+      if (!snat_static_mapping_match(sm, key0, &sm0, 1))
+        {
+          new_dst_addr0 = sm0.addr.as_u32;
+          new_dst_port0 = sm0.port;
+          vnet_buffer(b0)->sw_if_index[VLIB_TX] = sm0.fib_index;
+        }
+    }
+  else
+    {
+      si = value0.value;
+      if (sm->num_workers > 1)
+        {
+          k0.addr = ip0->dst_address;
+          k0.port = udp0->dst_port;
+          k0.fib_index = sm->outside_fib_index;
+          kv0.key = k0.as_u64;
+          if (clib_bihash_search_8_8 (&sm->worker_by_out, &kv0, &value0))
+            ASSERT(0);
+          else
+            ti = value0.value;
+        }
+      else
+        ti = sm->num_workers;
+
+      s0 = pool_elt_at_index (sm->per_thread_data[ti].sessions, si);
+      new_dst_addr0 = s0->in2out.addr.as_u32;
+      new_dst_port0 = s0->in2out.port;
+      vnet_buffer(b0)->sw_if_index[VLIB_TX] = s0->in2out.fib_index;
+    }
+
+  /* Destination is behind the same NAT, use internal address and port */
+  if (new_dst_addr0)
+    {
+      old_dst_addr0 = ip0->dst_address.as_u32;
+      ip0->dst_address.as_u32 = new_dst_addr0;
+      sum0 = ip0->checksum;
+      sum0 = ip_csum_update (sum0, old_dst_addr0, new_dst_addr0,
+                             ip4_header_t, dst_address);
+      ip0->checksum = ip_csum_fold (sum0);
+
+      old_dst_port0 = tcp0->ports.dst;
+      if (PREDICT_TRUE(new_dst_port0 != old_dst_port0))
+        {
+          if (PREDICT_TRUE(proto0 == SNAT_PROTOCOL_TCP))
+            {
+              tcp0->ports.dst = new_dst_port0;
+              sum0 = tcp0->checksum;
+              sum0 = ip_csum_update (sum0, old_dst_addr0, new_dst_addr0,
+                                     ip4_header_t, dst_address);
+              sum0 = ip_csum_update (sum0, old_dst_port0, new_dst_port0,
+                                     ip4_header_t /* cheat */, length);
+              tcp0->checksum = ip_csum_fold(sum0);
+            }
+          else
+            {
+              udp0->dst_port = new_dst_port0;
+              udp0->checksum = 0;
+            }
+        }
+    }
+}
+
 static inline uword
 snat_in2out_node_fn_inline (vlib_main_t * vm,
                             vlib_node_runtime_t * node,
@@ -594,6 +696,9 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               udp0->checksum = 0;
             }
 
+          /* Hairpinning */
+          snat_hairpinning (sm, b0, ip0, udp0, tcp0, proto0);
+
           /* Accounting */
           s0->last_heard = now;
           s0->total_pkts++;
@@ -739,6 +844,9 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               udp1->checksum = 0;
             }
 
+          /* Hairpinning */
+          snat_hairpinning (sm, b1, ip1, udp1, tcp1, proto1);
+
           /* Accounting */
           s1->last_heard = now;
           s1->total_pkts++;
@@ -919,6 +1027,9 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               udp0->checksum = 0;
             }
 
+          /* Hairpinning */
+          snat_hairpinning (sm, b0, ip0, udp0, tcp0, proto0);
+
           /* Accounting */
           s0->last_heard = now;
           s0->total_pkts++;
@@ -1430,6 +1541,9 @@ snat_in2out_fast_static_map_fn (vlib_main_t * vm,
                 }
             }
 
+          /* Hairpinning */
+          snat_hairpinning (sm, b0, ip0, udp0, tcp0, proto0);
+
         trace0:
           if (PREDICT_FALSE((node->flags & VLIB_NODE_FLAG_TRACE)
                             && (b0->flags & VLIB_BUFFER_IS_TRACED)))
diff --git a/test/test_snat.py b/test/test_snat.py
index e90d9c0b..5cc76f6c 100644
--- a/test/test_snat.py
+++ b/test/test_snat.py
@@ -34,6 +34,9 @@ class TestSNAT(VppTestCase):
                 i.config_ip4()
                 i.resolve_arp()
 
+            cls.pg0.generate_remote_hosts(2)
+            cls.pg0.configure_ipv4_neighbors()
+
             cls.overlapping_interfaces = list(list(cls.pg_interfaces[4:7]))
 
             for i in cls.overlapping_interfaces:
@@ -526,6 +529,70 @@ class TestSNAT(VppTestCase):
         capture = self.pg6.get_capture()
         self.verify_capture_in(capture, self.pg6)
 
+    def test_hairpinning(self):
+        """ SNAT hairpinning """
+
+        host = self.pg0.remote_hosts[0]
+        server = self.pg0.remote_hosts[1]
+        host_in_port = 1234
+        host_out_port = 0
+        server_in_port = 5678
+        server_out_port = 8765
+
+        self.snat_add_address(self.snat_addr)
+        self.vapi.snat_interface_add_del_feature(self.pg0.sw_if_index)
+        self.vapi.snat_interface_add_del_feature(self.pg1.sw_if_index,
+                                                 is_inside=0)
+        # add static mapping for server
+        self.snat_add_static_mapping(server.ip4, self.snat_addr,
+                                     server_in_port, server_out_port)
+
+        # send packet from host to server
+        p = (Ether(src=host.mac, dst=self.pg0.local_mac) /
+             IP(src=host.ip4, dst=self.snat_addr) /
+             TCP(sport=host_in_port, dport=server_out_port))
+        self.pg0.add_stream(p)
+        self.pg_enable_capture(self.pg_interfaces)
+        self.pg_start()
+        capture = self.pg0.get_capture()
+        self.assertEqual(1, len(capture))
+        p = capture[0]
+        try:
+            ip = p[IP]
+            tcp = p[TCP]
+            self.assertEqual(ip.src, self.snat_addr)
+            self.assertEqual(ip.dst, server.ip4)
+            self.assertNotEqual(tcp.sport, host_in_port)
+            self.assertEqual(tcp.dport, server_in_port)
+            host_out_port = tcp.sport
+        except:
+            error("Unexpected or invalid packet:")
+            error(p.show())
+            raise
+
+        # send reply from server to host
+        p = (Ether(src=server.mac, dst=self.pg0.local_mac) /
+             IP(src=server.ip4, dst=self.snat_addr) /
+             TCP(sport=server_in_port, dport=host_out_port))
+        self.pg0.add_stream(p)
+        self.pg_enable_capture(self.pg_interfaces)
+        self.pg_start()
+        capture = self.pg0.get_capture()
+        self.assertEqual(1, len(capture))
+        p = capture[0]
+        try:
+            ip = p[IP]
+            tcp = p[TCP]
+            self.assertEqual(ip.src, self.snat_addr)
+            self.assertEqual(ip.dst, host.ip4)
+            self.assertEqual(tcp.sport, server_out_port)
+            self.assertEqual(tcp.dport, host_in_port)
+        except:
+            error("Unexpected or invalid packet:")
+            error(p.show())
+            raise
+
+
     def tearDown(self):
         super(TestSNAT, self).tearDown()
         if not self.vpp_dead: