nat: Revert "nat: respect udp checksum"

This reverts commit 80276a7101f23ddd7207983f48f85422daf2cb7f.

The commit in master was found to be wrong, was reverted, and replaced by 16572355c9069e2e8e4836dc6bd6a65feed2d390

This reverts the corresponding commit in stable/1908, to replace with the correct fix.

Type: fix
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Change-Id: Idc27c0d81edf2263e523088f7ee7b66655db20f1

6 files changed, 166 insertions, 428 deletions

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