nat: respect udp checksum

Type: fix

Change-Id: I73895fa0101bd50483160c8dc6faac2c67513077
Signed-off-by: Filip Varga <fivarga@cisco.com>
(cherry picked from commit 0d75f783644a24b219ed79d9f9c17387783f67ca)

6 files changed, 428 insertions, 166 deletions

diff --git a/src/plugins/nat/in2out.c b/src/plugins/nat/in2out.c
index c69bc61236b..802202d7939 100755
--- a/src/plugins/nat/in2out.c
+++ b/src/plugins/nat/in2out.c
@@ -1075,12 +1075,11 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 				 src_address /* changed member */ );
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->src_port;
+	  new_port0 = udp0->src_port = s0->out2in.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port0 = tcp0->src_port;
-	      tcp0->src_port = s0->out2in.port;
-	      new_port0 = tcp0->src_port;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
 				     ip4_header_t,
@@ -1094,9 +1093,17 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 	    }
 	  else
 	    {
-	      old_port0 = udp0->src_port;
-	      udp0->src_port = s0->out2in.port;
-	      udp0->checksum = 0;
+	      if (PREDICT_FALSE (udp0->checksum))
+		{
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	      udp_packets++;
 	    }
 
@@ -1264,12 +1271,11 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 				 src_address /* changed member */ );
 	  ip1->checksum = ip_csum_fold (sum1);
 
+	  old_port1 = udp1->src_port;
+	  new_port1 = udp1->src_port = s1->out2in.port;
+
 	  if (PREDICT_TRUE (proto1 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port1 = tcp1->src_port;
-	      tcp1->src_port = s1->out2in.port;
-	      new_port1 = tcp1->src_port;
-
 	      sum1 = tcp1->checksum;
 	      sum1 = ip_csum_update (sum1, old_addr1, new_addr1,
 				     ip4_header_t,
@@ -1283,9 +1289,17 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 	    }
 	  else
 	    {
-	      old_port1 = udp1->src_port;
-	      udp1->src_port = s1->out2in.port;
-	      udp1->checksum = 0;
+	      if (PREDICT_FALSE (udp1->checksum))
+		{
+		  sum1 = udp1->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 */ );
+		  udp1->checksum = ip_csum_fold (sum1);
+		}
 	      udp_packets++;
 	    }
 
@@ -1488,12 +1502,11 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 				 src_address /* changed member */ );
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->src_port;
+	  new_port0 = udp0->src_port = s0->out2in.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port0 = tcp0->src_port;
-	      tcp0->src_port = s0->out2in.port;
-	      new_port0 = tcp0->src_port;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
 				     ip4_header_t,
@@ -1507,9 +1520,17 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 	    }
 	  else
 	    {
-	      old_port0 = udp0->src_port;
-	      udp0->src_port = s0->out2in.port;
-	      udp0->checksum = 0;
+	      if (PREDICT_FALSE (udp0->checksum))
+		{
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	      udp_packets++;
 	    }
 
@@ -1869,12 +1890,11 @@ VLIB_NODE_FN (nat44_in2out_reass_node) (vlib_main_t * vm,
 
 	  if (PREDICT_FALSE (ip4_is_first_fragment (ip0)))
 	    {
+	      old_port0 = udp0->src_port;
+	      new_port0 = udp0->src_port = s0->out2in.port;
+
 	      if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 		{
-		  old_port0 = tcp0->src_port;
-		  tcp0->src_port = s0->out2in.port;
-		  new_port0 = tcp0->src_port;
-
 		  sum0 = tcp0->checksum;
 		  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
 					 ip4_header_t,
@@ -1884,11 +1904,16 @@ VLIB_NODE_FN (nat44_in2out_reass_node) (vlib_main_t * vm,
 					 length /* changed member */ );
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
-	      else
+	      else if (PREDICT_FALSE (udp0->checksum))
 		{
-		  old_port0 = udp0->src_port;
-		  udp0->src_port = s0->out2in.port;
-		  udp0->checksum = 0;
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
 		}
 	    }
 
@@ -2099,11 +2124,11 @@ VLIB_NODE_FN (snat_in2out_fast_node) (vlib_main_t * vm,
 
 	  if (PREDICT_FALSE (new_port0 != udp0->dst_port))
 	    {
+	      old_port0 = udp0->src_port;
+	      udp0->src_port = new_port0;
+
 	      if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 		{
-		  old_port0 = tcp0->src_port;
-		  tcp0->src_port = new_port0;
-
 		  sum0 = tcp0->checksum;
 		  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
 					 ip4_header_t,
@@ -2114,11 +2139,16 @@ VLIB_NODE_FN (snat_in2out_fast_node) (vlib_main_t * vm,
 		  mss_clamping (sm, tcp0, &sum0);
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
-	      else
+	      else if (udp0->checksum)
 		{
-		  old_port0 = udp0->src_port;
-		  udp0->src_port = new_port0;
-		  udp0->checksum = 0;
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
 		}
 	    }
 	  else
@@ -2132,6 +2162,14 @@ VLIB_NODE_FN (snat_in2out_fast_node) (vlib_main_t * vm,
 		  mss_clamping (sm, tcp0, &sum0);
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
+	      else if (udp0->checksum)
+		{
+		  sum0 = udp0->checksum;
+		  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+					 ip4_header_t,
+					 dst_address /* changed member */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	    }
 
 	  /* Hairpinning */
diff --git a/src/plugins/nat/in2out_ed.c b/src/plugins/nat/in2out_ed.c
index de00c6e7b13..c878dddd13e 100644
--- a/src/plugins/nat/in2out_ed.c
+++ b/src/plugins/nat/in2out_ed.c
@@ -1045,11 +1045,11 @@ nat44_ed_in2out_node_fn_inline (vlib_main_t * vm,
 				   dst_address);
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->src_port;
+	  new_port0 = udp0->src_port = s0->out2in.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port0 = tcp0->src_port;
-	      new_port0 = tcp0->src_port = s0->out2in.port;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
 				     dst_address);
@@ -1073,10 +1073,29 @@ nat44_ed_in2out_node_fn_inline (vlib_main_t * vm,
 		  (sm, s0, tcp0, thread_index))
 		goto trace00;
 	    }
+	  else if (udp0->checksum)
+	    {
+	      sum0 = udp0->checksum;
+	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+				     dst_address);
+	      sum0 = ip_csum_update (sum0, old_port0, new_port0, ip4_header_t,
+				     length);
+	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
+		{
+		  sum0 = ip_csum_update (sum0, ip0->dst_address.as_u32,
+					 s0->ext_host_addr.as_u32,
+					 ip4_header_t, dst_address);
+		  sum0 = ip_csum_update (sum0, tcp0->dst_port,
+					 s0->ext_host_port, ip4_header_t,
+					 length);
+		  udp0->dst_port = s0->ext_host_port;
+		  ip0->dst_address.as_u32 = s0->ext_host_addr.as_u32;
+		}
+	      udp0->checksum = ip_csum_fold (sum0);
+	      udp_packets++;
+	    }
 	  else
 	    {
-	      udp0->src_port = s0->out2in.port;
-	      udp0->checksum = 0;
 	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
 		{
 		  udp0->dst_port = s0->ext_host_port;
@@ -1255,11 +1274,11 @@ nat44_ed_in2out_node_fn_inline (vlib_main_t * vm,
 				   dst_address);
 	  ip1->checksum = ip_csum_fold (sum1);
 
+	  old_port1 = udp1->src_port;
+	  new_port1 = udp1->src_port = s1->out2in.port;
+
 	  if (PREDICT_TRUE (proto1 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port1 = tcp1->src_port;
-	      new_port1 = tcp1->src_port = s1->out2in.port;
-
 	      sum1 = tcp1->checksum;
 	      sum1 = ip_csum_update (sum1, old_addr1, new_addr1, ip4_header_t,
 				     dst_address);
@@ -1283,10 +1302,30 @@ nat44_ed_in2out_node_fn_inline (vlib_main_t * vm,
 		  (sm, s1, tcp1, thread_index))
 		goto trace01;
 	    }
+	  else if (udp1->checksum)
+	    {
+	      sum1 = udp1->checksum;
+	      sum1 = ip_csum_update (sum1, old_addr1, new_addr1, ip4_header_t,
+				     dst_address);
+	      sum1 = ip_csum_update (sum1, old_port1, new_port1, ip4_header_t,
+				     length);
+
+	      if (PREDICT_FALSE (is_twice_nat_session (s1)))
+		{
+		  sum1 = ip_csum_update (sum1, ip1->dst_address.as_u32,
+					 s1->ext_host_addr.as_u32,
+					 ip4_header_t, dst_address);
+		  sum1 = ip_csum_update (sum1, tcp1->dst_port,
+					 s1->ext_host_port, ip4_header_t,
+					 length);
+		  udp1->dst_port = s1->ext_host_port;
+		  ip1->dst_address.as_u32 = s1->ext_host_addr.as_u32;
+		}
+	      udp1->checksum = ip_csum_fold (sum1);
+	      udp_packets++;
+	    }
 	  else
 	    {
-	      udp1->src_port = s1->out2in.port;
-	      udp1->checksum = 0;
 	      if (PREDICT_FALSE (is_twice_nat_session (s1)))
 		{
 		  udp1->dst_port = s1->ext_host_port;
@@ -1493,11 +1532,11 @@ nat44_ed_in2out_node_fn_inline (vlib_main_t * vm,
 				   dst_address);
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->src_port;
+	  new_port0 = udp0->src_port = s0->out2in.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port0 = tcp0->src_port;
-	      new_port0 = tcp0->src_port = s0->out2in.port;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
 				     dst_address);
@@ -1521,10 +1560,29 @@ nat44_ed_in2out_node_fn_inline (vlib_main_t * vm,
 		  (sm, s0, tcp0, thread_index))
 		goto trace0;
 	    }
+	  else if (udp0->checksum)
+	    {
+	      sum0 = udp0->checksum;
+	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+				     dst_address);
+	      sum0 = ip_csum_update (sum0, old_port0, new_port0, ip4_header_t,
+				     length);
+	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
+		{
+		  sum0 = ip_csum_update (sum0, ip0->dst_address.as_u32,
+					 s0->ext_host_addr.as_u32,
+					 ip4_header_t, dst_address);
+		  sum0 = ip_csum_update (sum0, tcp0->dst_port,
+					 s0->ext_host_port, ip4_header_t,
+					 length);
+		  udp0->dst_port = s0->ext_host_port;
+		  ip0->dst_address.as_u32 = s0->ext_host_addr.as_u32;
+		}
+	      udp0->checksum = ip_csum_fold (sum0);
+	      udp_packets++;
+	    }
 	  else
 	    {
-	      udp0->src_port = s0->out2in.port;
-	      udp0->checksum = 0;
 	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
 		{
 		  udp0->dst_port = s0->ext_host_port;
@@ -1915,12 +1973,11 @@ nat44_ed_in2out_reass_node_fn_inline (vlib_main_t * vm,
 
 	  if (PREDICT_FALSE (ip4_is_first_fragment (ip0)))
 	    {
+	      old_port0 = udp0->src_port;
+	      new_port0 = udp0->src_port = s0->out2in.port;
+
 	      if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 		{
-		  old_port0 = tcp0->src_port;
-		  tcp0->src_port = s0->out2in.port;
-		  new_port0 = tcp0->src_port;
-
 		  sum0 = tcp0->checksum;
 		  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
 					 ip4_header_t,
@@ -1941,11 +1998,30 @@ nat44_ed_in2out_reass_node_fn_inline (vlib_main_t * vm,
 		    }
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
+	      else if (udp0->checksum)
+		{
+		  sum0 = udp0->checksum;
+		  sum0 =
+		    ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+				    dst_address);
+		  sum0 =
+		    ip_csum_update (sum0, old_port0, new_port0, ip4_header_t,
+				    length);
+		  if (PREDICT_FALSE (is_twice_nat_session (s0)))
+		    {
+		      sum0 = ip_csum_update (sum0, ip0->dst_address.as_u32,
+					     s0->ext_host_addr.as_u32,
+					     ip4_header_t, dst_address);
+		      sum0 = ip_csum_update (sum0, tcp0->dst_port,
+					     s0->ext_host_port, ip4_header_t,
+					     length);
+		      udp0->dst_port = s0->ext_host_port;
+		      ip0->dst_address.as_u32 = s0->ext_host_addr.as_u32;
+		    }
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	      else
 		{
-		  old_port0 = udp0->src_port;
-		  udp0->src_port = s0->out2in.port;
-		  udp0->checksum = 0;
 		  if (PREDICT_FALSE (is_twice_nat_session (s0)))
 		    {
 		      udp0->dst_port = s0->ext_host_port;
diff --git a/src/plugins/nat/nat_det_in2out.c b/src/plugins/nat/nat_det_in2out.c
index 918e1f5f9c0..832a2bae947 100644
--- a/src/plugins/nat/nat_det_in2out.c
+++ b/src/plugins/nat/nat_det_in2out.c
@@ -392,7 +392,8 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 		}
 	    }
 
-	  new_port0 = ses0->out.out_port;
+	  old_port0 = udp0->src_port;
+	  udp0->src_port = new_port0 = ses0->out.out_port;
 
 	  old_addr0.as_u32 = ip0->src_address.as_u32;
 	  ip0->src_address.as_u32 = new_addr0.as_u32;
@@ -424,9 +425,6 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 		       && ses0->state == SNAT_SESSION_UNKNOWN)
 		ses0->state = SNAT_SESSION_TCP_ESTABLISHED;
 
-	      old_port0 = tcp0->src;
-	      tcp0->src = new_port0;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0.as_u32, new_addr0.as_u32,
 				     ip4_header_t,
@@ -440,9 +438,20 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 	  else
 	    {
 	      ses0->state = SNAT_SESSION_UDP_ACTIVE;
-	      old_port0 = udp0->src_port;
-	      udp0->src_port = new_port0;
-	      udp0->checksum = 0;
+
+	      if (PREDICT_FALSE (udp0->checksum))
+		{
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	    }
 
 	  switch (ses0->state)
@@ -556,7 +565,8 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 		}
 	    }
 
-	  new_port1 = ses1->out.out_port;
+	  old_port1 = udp1->src_port;
+	  udp1->src_port = new_port1 = ses1->out.out_port;
 
 	  old_addr1.as_u32 = ip1->src_address.as_u32;
 	  ip1->src_address.as_u32 = new_addr1.as_u32;
@@ -588,9 +598,6 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 		       && ses1->state == SNAT_SESSION_UNKNOWN)
 		ses1->state = SNAT_SESSION_TCP_ESTABLISHED;
 
-	      old_port1 = tcp1->src;
-	      tcp1->src = new_port1;
-
 	      sum1 = tcp1->checksum;
 	      sum1 = ip_csum_update (sum1, old_addr1.as_u32, new_addr1.as_u32,
 				     ip4_header_t,
@@ -604,9 +611,20 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 	  else
 	    {
 	      ses1->state = SNAT_SESSION_UDP_ACTIVE;
-	      old_port1 = udp1->src_port;
-	      udp1->src_port = new_port1;
-	      udp1->checksum = 0;
+
+	      if (PREDICT_FALSE (udp1->checksum))
+		{
+		  sum1 = udp1->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 */ );
+		  udp1->checksum = ip_csum_fold (sum1);
+		}
 	    }
 
 	  switch (ses1->state)
@@ -756,7 +774,8 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 		}
 	    }
 
-	  new_port0 = ses0->out.out_port;
+	  old_port0 = udp0->src_port;
+	  udp0->src_port = new_port0 = ses0->out.out_port;
 
 	  old_addr0.as_u32 = ip0->src_address.as_u32;
 	  ip0->src_address.as_u32 = new_addr0.as_u32;
@@ -788,9 +807,6 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 		       && ses0->state == SNAT_SESSION_UNKNOWN)
 		ses0->state = SNAT_SESSION_TCP_ESTABLISHED;
 
-	      old_port0 = tcp0->src;
-	      tcp0->src = new_port0;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0.as_u32, new_addr0.as_u32,
 				     ip4_header_t,
@@ -804,9 +820,20 @@ VLIB_NODE_FN (snat_det_in2out_node) (vlib_main_t * vm,
 	  else
 	    {
 	      ses0->state = SNAT_SESSION_UDP_ACTIVE;
-	      old_port0 = udp0->src_port;
-	      udp0->src_port = new_port0;
-	      udp0->checksum = 0;
+
+	      if (PREDICT_FALSE (udp0->checksum))
+		{
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	    }
 
 	  switch (ses0->state)
diff --git a/src/plugins/nat/nat_det_out2in.c b/src/plugins/nat/nat_det_out2in.c
index 45fba18b248..c4bd096deb1 100644
--- a/src/plugins/nat/nat_det_out2in.c
+++ b/src/plugins/nat/nat_det_out2in.c
@@ -343,7 +343,8 @@ VLIB_NODE_FN (snat_det_out2in_node) (vlib_main_t * vm,
 	      b0->error = node->errors[NAT_DET_OUT2IN_ERROR_NO_TRANSLATION];
 	      goto trace0;
 	    }
-	  new_port0 = ses0->in_port;
+	  old_port0 = udp0->dst_port;
+	  udp0->dst_port = new_port0 = ses0->in_port;
 
 	  old_addr0 = ip0->dst_address;
 	  ip0->dst_address = new_addr0;
@@ -364,24 +365,25 @@ VLIB_NODE_FN (snat_det_out2in_node) (vlib_main_t * vm,
 		       && 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
+	  else if (udp0->checksum)
 	    {
-	      old_port0 = udp0->dst_port;
-	      udp0->dst_port = new_port0;
-	      udp0->checksum = 0;
+	      sum0 = udp0->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 */ );
+	      udp0->checksum = ip_csum_fold (sum0);
 	    }
 
 	trace0:
@@ -462,7 +464,8 @@ VLIB_NODE_FN (snat_det_out2in_node) (vlib_main_t * vm,
 	      b1->error = node->errors[NAT_DET_OUT2IN_ERROR_NO_TRANSLATION];
 	      goto trace1;
 	    }
-	  new_port1 = ses1->in_port;
+	  old_port1 = udp1->dst_port;
+	  udp1->dst_port = new_port1 = ses1->in_port;
 
 	  old_addr1 = ip1->dst_address;
 	  ip1->dst_address = new_addr1;
@@ -483,24 +486,25 @@ VLIB_NODE_FN (snat_det_out2in_node) (vlib_main_t * vm,
 		       && 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
+	  else if (udp1->checksum)
 	    {
-	      old_port1 = udp1->dst_port;
-	      udp1->dst_port = new_port1;
-	      udp1->checksum = 0;
+	      sum1 = udp1->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 */ );
+	      udp1->checksum = ip_csum_fold (sum1);
 	    }
 
 	trace1:
@@ -614,7 +618,8 @@ VLIB_NODE_FN (snat_det_out2in_node) (vlib_main_t * vm,
 	      b0->error = node->errors[NAT_DET_OUT2IN_ERROR_NO_TRANSLATION];
 	      goto trace00;
 	    }
-	  new_port0 = ses0->in_port;
+	  old_port0 = udp0->dst_port;
+	  udp0->dst_port = new_port0 = ses0->in_port;
 
 	  old_addr0 = ip0->dst_address;
 	  ip0->dst_address = new_addr0;
@@ -635,24 +640,25 @@ VLIB_NODE_FN (snat_det_out2in_node) (vlib_main_t * vm,
 		       && 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
+	  else if (udp0->checksum)
 	    {
-	      old_port0 = udp0->dst_port;
-	      udp0->dst_port = new_port0;
-	      udp0->checksum = 0;
+	      sum0 = udp0->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 */ );
+	      udp0->checksum = ip_csum_fold (sum0);
 	    }
 
 	trace00:
diff --git a/src/plugins/nat/out2in.c b/src/plugins/nat/out2in.c
index 8c6cb482703..83c099d1bd2 100755
--- a/src/plugins/nat/out2in.c
+++ b/src/plugins/nat/out2in.c
@@ -893,6 +893,9 @@ VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
 				 dst_address /* changed member */ );
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->dst_port;
+	  new_port0 = udp0->dst_port = s0->in2out.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
 	      old_port0 = tcp0->dst_port;
@@ -912,9 +915,17 @@ VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
 	    }
 	  else
 	    {
-	      old_port0 = udp0->dst_port;
-	      udp0->dst_port = s0->in2out.port;
-	      udp0->checksum = 0;
+	      if (PREDICT_FALSE (udp0->checksum))
+		{
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	      udp_packets++;
 	    }
 
@@ -1059,12 +1070,11 @@ VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
 				 dst_address /* changed member */ );
 	  ip1->checksum = ip_csum_fold (sum1);
 
+	  old_port1 = udp1->dst_port;
+	  new_port1 = udp1->dst_port = s1->in2out.port;
+
 	  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,
@@ -1078,9 +1088,17 @@ VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
 	    }
 	  else
 	    {
-	      old_port1 = udp1->dst_port;
-	      udp1->dst_port = s1->in2out.port;
-	      udp1->checksum = 0;
+	      if (PREDICT_FALSE (udp1->checksum))
+		{
+		  sum1 = udp1->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 */ );
+		  udp1->checksum = ip_csum_fold (sum1);
+		}
 	      udp_packets++;
 	    }
 
@@ -1262,12 +1280,11 @@ VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
 				 dst_address /* changed member */ );
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->dst_port;
+	  new_port0 = udp0->dst_port = s0->in2out.port;
+
 	  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,
@@ -1281,9 +1298,17 @@ VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
 	    }
 	  else
 	    {
-	      old_port0 = udp0->dst_port;
-	      udp0->dst_port = s0->in2out.port;
-	      udp0->checksum = 0;
+	      if (PREDICT_FALSE (udp0->checksum))
+		{
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	      udp_packets++;
 	    }
 
@@ -1573,12 +1598,11 @@ VLIB_NODE_FN (nat44_out2in_reass_node) (vlib_main_t * vm,
 
 	  if (PREDICT_FALSE (ip4_is_first_fragment (ip0)))
 	    {
+	      old_port0 = udp0->dst_port;
+	      new_port0 = udp0->dst_port = s0->in2out.port;
+
 	      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,
@@ -1589,11 +1613,16 @@ VLIB_NODE_FN (nat44_out2in_reass_node) (vlib_main_t * vm,
 					 length /* changed member */ );
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
-	      else
+	      else if (udp0->checksum)
 		{
-		  old_port0 = udp0->dst_port;
-		  udp0->dst_port = s0->in2out.port;
-		  udp0->checksum = 0;
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
 		}
 	    }
 
@@ -1797,26 +1826,30 @@ VLIB_NODE_FN (snat_out2in_fast_node) (vlib_main_t * vm,
 
 	  if (PREDICT_FALSE (new_port0 != udp0->dst_port))
 	    {
+	      old_port0 = udp0->dst_port;
+	      udp0->dst_port = new_port0;
+
 	      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
+	      else if (udp0->checksum)
 		{
-		  old_port0 = udp0->dst_port;
-		  udp0->dst_port = new_port0;
-		  udp0->checksum = 0;
+		  sum0 = udp0->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 */ );
+		  udp0->checksum = ip_csum_fold (sum0);
 		}
 	    }
 	  else
@@ -1827,9 +1860,16 @@ VLIB_NODE_FN (snat_out2in_fast_node) (vlib_main_t * vm,
 		  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
 					 ip4_header_t,
 					 dst_address /* changed member */ );
-
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
+	      else if (udp0->checksum)
+		{
+		  sum0 = udp0->checksum;
+		  sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
+					 ip4_header_t,
+					 dst_address /* changed member */ );
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	    }
 
 	trace00:
diff --git a/src/plugins/nat/out2in_ed.c b/src/plugins/nat/out2in_ed.c
index 50abebd9cfb..2067c512b92 100644
--- a/src/plugins/nat/out2in_ed.c
+++ b/src/plugins/nat/out2in_ed.c
@@ -919,11 +919,11 @@ nat44_ed_out2in_node_fn_inline (vlib_main_t * vm,
 				   src_address);
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->dst_port;
+	  new_port0 = udp0->dst_port = s0->in2out.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port0 = tcp0->dst_port;
-	      new_port0 = tcp0->dst_port = s0->in2out.port;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
 				     dst_address);
@@ -946,15 +946,34 @@ nat44_ed_out2in_node_fn_inline (vlib_main_t * vm,
 		  (sm, s0, tcp0, thread_index))
 		goto trace00;
 	    }
+	  else if (udp0->checksum)
+	    {
+	      sum0 = udp0->checksum;
+	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+				     dst_address);
+	      sum0 = ip_csum_update (sum0, old_port0, new_port0, ip4_header_t,
+				     length);
+	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
+		{
+		  sum0 = ip_csum_update (sum0, ip0->src_address.as_u32,
+					 s0->ext_host_nat_addr.as_u32,
+					 ip4_header_t, dst_address);
+		  sum0 = ip_csum_update (sum0, udp0->src_port,
+					 s0->ext_host_nat_port, ip4_header_t,
+					 length);
+		  udp0->src_port = s0->ext_host_nat_port;
+		  ip0->src_address.as_u32 = s0->ext_host_nat_addr.as_u32;
+		}
+	      udp0->checksum = ip_csum_fold (sum0);
+	      udp_packets++;
+	    }
 	  else
 	    {
-	      udp0->dst_port = s0->in2out.port;
-	      if (is_twice_nat_session (s0))
+	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
 		{
 		  udp0->src_port = s0->ext_host_nat_port;
 		  ip0->src_address.as_u32 = s0->ext_host_nat_addr.as_u32;
 		}
-	      udp0->checksum = 0;
 	      udp_packets++;
 	    }
 
@@ -1157,11 +1176,11 @@ nat44_ed_out2in_node_fn_inline (vlib_main_t * vm,
 				   src_address);
 	  ip1->checksum = ip_csum_fold (sum1);
 
+	  old_port1 = udp1->dst_port;
+	  new_port1 = udp1->dst_port = s1->in2out.port;
+
 	  if (PREDICT_TRUE (proto1 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port1 = tcp1->dst_port;
-	      new_port1 = tcp1->dst_port = s1->in2out.port;
-
 	      sum1 = tcp1->checksum;
 	      sum1 = ip_csum_update (sum1, old_addr1, new_addr1, ip4_header_t,
 				     dst_address);
@@ -1184,15 +1203,34 @@ nat44_ed_out2in_node_fn_inline (vlib_main_t * vm,
 		  (sm, s1, tcp1, thread_index))
 		goto trace01;
 	    }
+	  else if (udp1->checksum)
+	    {
+	      sum1 = udp1->checksum;
+	      sum1 = ip_csum_update (sum1, old_addr1, new_addr1, ip4_header_t,
+				     dst_address);
+	      sum1 = ip_csum_update (sum1, old_port1, new_port1, ip4_header_t,
+				     length);
+	      if (PREDICT_FALSE (is_twice_nat_session (s1)))
+		{
+		  sum1 = ip_csum_update (sum1, ip1->src_address.as_u32,
+					 s1->ext_host_nat_addr.as_u32,
+					 ip4_header_t, dst_address);
+		  sum1 = ip_csum_update (sum1, udp1->src_port,
+					 s1->ext_host_nat_port, ip4_header_t,
+					 length);
+		  udp1->src_port = s1->ext_host_nat_port;
+		  ip1->src_address.as_u32 = s1->ext_host_nat_addr.as_u32;
+		}
+	      udp1->checksum = ip_csum_fold (sum1);
+	      udp_packets++;
+	    }
 	  else
 	    {
-	      udp1->dst_port = s1->in2out.port;
-	      if (is_twice_nat_session (s1))
+	      if (PREDICT_FALSE (is_twice_nat_session (s1)))
 		{
 		  udp1->src_port = s1->ext_host_nat_port;
 		  ip1->src_address.as_u32 = s1->ext_host_nat_addr.as_u32;
 		}
-	      udp1->checksum = 0;
 	      udp_packets++;
 	    }
 
@@ -1429,11 +1467,11 @@ nat44_ed_out2in_node_fn_inline (vlib_main_t * vm,
 				   src_address);
 	  ip0->checksum = ip_csum_fold (sum0);
 
+	  old_port0 = udp0->dst_port;
+	  new_port0 = udp0->dst_port = s0->in2out.port;
+
 	  if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
 	    {
-	      old_port0 = tcp0->dst_port;
-	      new_port0 = tcp0->dst_port = s0->in2out.port;
-
 	      sum0 = tcp0->checksum;
 	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
 				     dst_address);
@@ -1456,15 +1494,34 @@ nat44_ed_out2in_node_fn_inline (vlib_main_t * vm,
 		  (sm, s0, tcp0, thread_index))
 		goto trace0;
 	    }
+	  else if (udp0->checksum)
+	    {
+	      sum0 = udp0->checksum;
+	      sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+				     dst_address);
+	      sum0 = ip_csum_update (sum0, old_port0, new_port0, ip4_header_t,
+				     length);
+	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
+		{
+		  sum0 = ip_csum_update (sum0, ip0->src_address.as_u32,
+					 s0->ext_host_nat_addr.as_u32,
+					 ip4_header_t, dst_address);
+		  sum0 = ip_csum_update (sum0, udp0->src_port,
+					 s0->ext_host_nat_port, ip4_header_t,
+					 length);
+		  udp0->src_port = s0->ext_host_nat_port;
+		  ip0->src_address.as_u32 = s0->ext_host_nat_addr.as_u32;
+		}
+	      udp0->checksum = ip_csum_fold (sum0);
+	      udp_packets++;
+	    }
 	  else
 	    {
-	      udp0->dst_port = s0->in2out.port;
-	      if (is_twice_nat_session (s0))
+	      if (PREDICT_FALSE (is_twice_nat_session (s0)))
 		{
 		  udp0->src_port = s0->ext_host_nat_port;
 		  ip0->src_address.as_u32 = s0->ext_host_nat_addr.as_u32;
 		}
-	      udp0->checksum = 0;
 	      udp_packets++;
 	    }
 
@@ -1818,12 +1875,11 @@ VLIB_NODE_FN (nat44_ed_out2in_reass_node) (vlib_main_t * vm,
 
 	  if (PREDICT_FALSE (ip4_is_first_fragment (ip0)))
 	    {
+	      old_port0 = udp0->dst_port;
+	      new_port0 = udp0->dst_port = s0->in2out.port;
+
 	      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,
@@ -1845,16 +1901,35 @@ VLIB_NODE_FN (nat44_ed_out2in_reass_node) (vlib_main_t * vm,
 		    }
 		  tcp0->checksum = ip_csum_fold (sum0);
 		}
+	      else if (udp0->checksum)
+		{
+		  sum0 = udp0->checksum;
+		  sum0 =
+		    ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
+				    dst_address);
+		  sum0 =
+		    ip_csum_update (sum0, old_port0, new_port0, ip4_header_t,
+				    length);
+		  if (PREDICT_FALSE (is_twice_nat_session (s0)))
+		    {
+		      sum0 = ip_csum_update (sum0, ip0->src_address.as_u32,
+					     s0->ext_host_nat_addr.as_u32,
+					     ip4_header_t, dst_address);
+		      sum0 = ip_csum_update (sum0, udp0->src_port,
+					     s0->ext_host_nat_port,
+					     ip4_header_t, length);
+		      udp0->src_port = s0->ext_host_nat_port;
+		      ip0->src_address.as_u32 = s0->ext_host_nat_addr.as_u32;
+		    }
+		  udp0->checksum = ip_csum_fold (sum0);
+		}
 	      else
 		{
-		  old_port0 = udp0->dst_port;
-		  udp0->dst_port = s0->in2out.port;
-		  if (is_twice_nat_session (s0))
+		  if (PREDICT_FALSE (is_twice_nat_session (s0)))
 		    {
 		      udp0->src_port = s0->ext_host_nat_port;
 		      ip0->src_address.as_u32 = s0->ext_host_nat_addr.as_u32;
 		    }
-		  udp0->checksum = 0;
 		}
 	    }