nat: TCP state tracking based on RFC 7857/RFC 6146

Implement proper state machine based on above RFCs. ACKs to SYNs/FINs
are no longer required/tracked. This is more friendly to peers and
accounts for lost packets and retransmits.

This change also means that all traffic is translated and forwarded
while in transitory timeout, which helps delivering e.g. retransmitted
FINs, FINACKs and other messages.

Also support reopening a session in transitory timeout after seeing both
FINs by seeing both SYNs again. This helps quick connection
reestablishment if the peers want to.

Type: improvement
Signed-off-by: Klement Sekera <ksekera@cisco.com>
Signed-off-by: Miklos Tirpak <miklos.tirpak@gmail.com>
Change-Id: Ibf521c79463472db97e593bfa02b32b4a06dfd2a

1 files changed, 13 insertions, 41 deletions

diff --git a/src/plugins/nat/nat44-ed/nat44_ed_out2in.c b/src/plugins/nat/nat44-ed/nat44_ed_out2in.c
index 5ad57a17098..40a72122140 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_out2in.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_out2in.c
@@ -41,7 +41,6 @@ typedef enum
   NAT_ED_SP_REASON_NO_REASON,
   NAT_ED_SP_REASON_LOOKUP_FAILED,
   NAT_ED_SP_REASON_VRF_EXPIRED,
-  NAT_ED_SP_TCP_CLOSED,
   NAT_ED_SP_SESS_EXPIRED,
 } nat_slow_path_reason_e;
 
@@ -57,6 +56,7 @@ typedef struct
   u8 is_slow_path;
   u8 translation_via_i2of;
   u8 lookup_skipped;
+  u8 tcp_state;
   nat_slow_path_reason_e slow_path_reason;
 } nat44_ed_out2in_trace_t;
 
@@ -72,8 +72,6 @@ format_slow_path_reason (u8 *s, va_list *args)
       return format (s, "slow path because lookup failed");
     case NAT_ED_SP_REASON_VRF_EXPIRED:
       return format (s, "slow path because vrf expired");
-    case NAT_ED_SP_TCP_CLOSED:
-      return format (s, "slow path because tcp closed");
     case NAT_ED_SP_SESS_EXPIRED:
       return format (s, "slow path because session expired");
     }
@@ -107,14 +105,19 @@ format_nat44_ed_out2in_trace (u8 * s, va_list * args)
     {
       if (t->lookup_skipped)
 	{
-	  s = format (s, "\n lookup skipped - cached session index used");
+	  s = format (s, "\n  lookup skipped - cached session index used");
 	}
       else
 	{
 	  s = format (s, "\n  search key %U", format_ed_session_kvp,
 		      &t->search_key);
 	}
-      s = format (s, "\n %U", format_slow_path_reason, t->slow_path_reason);
+      s = format (s, "\n  %U", format_slow_path_reason, t->slow_path_reason);
+    }
+  if (IP_PROTOCOL_TCP == t->i2of.match.proto)
+    {
+      s = format (s, "\n  TCP state: %U", format_nat44_ed_tcp_state,
+		  t->tcp_state);
     }
 
   return s;
@@ -645,10 +648,9 @@ create_bypass_for_fwd (snat_main_t *sm, vlib_buffer_t *b, snat_session_t *s,
 
   if (ip->protocol == IP_PROTOCOL_TCP)
     {
-      tcp_header_t *tcp = ip4_next_header (ip);
-      nat44_set_tcp_session_state_o2i (sm, now, s, tcp->flags,
-				       tcp->ack_number, tcp->seq_number,
-				       thread_index);
+      nat44_set_tcp_session_state_o2i (
+	sm, now, s, vnet_buffer (b)->ip.reass.icmp_type_or_tcp_flags,
+	thread_index);
     }
 
   /* Accounting */
@@ -883,23 +885,6 @@ nat44_ed_out2in_fast_path_node_fn_inline (vlib_main_t * vm,
 	  goto trace0;
 	}
 
-      if (s0->tcp_closed_timestamp)
-	{
-	  if (now >= s0->tcp_closed_timestamp)
-	    {
-	      // session is closed, go slow path, freed in slow path
-	      slow_path_reason = NAT_ED_SP_TCP_CLOSED;
-	      next[0] = NAT_NEXT_OUT2IN_ED_SLOW_PATH;
-	    }
-	  else
-	    {
-	      // session in transitory timeout, drop
-	      b0->error = node->errors[NAT_OUT2IN_ED_ERROR_TCP_CLOSED];
-	      next[0] = NAT_NEXT_DROP;
-	    }
-	  goto trace0;
-	}
-
       // drop if session expired
       u64 sess_timeout_time;
       sess_timeout_time =
@@ -981,10 +966,6 @@ nat44_ed_out2in_fast_path_node_fn_inline (vlib_main_t * vm,
 	  nat44_set_tcp_session_state_o2i (sm, now, s0,
 					   vnet_buffer (b0)->ip.
 					   reass.icmp_type_or_tcp_flags,
-					   vnet_buffer (b0)->ip.
-					   reass.tcp_ack_number,
-					   vnet_buffer (b0)->ip.
-					   reass.tcp_seq_number,
 					   thread_index);
 	  break;
 	case IP_PROTOCOL_UDP:
@@ -1028,6 +1009,7 @@ nat44_ed_out2in_fast_path_node_fn_inline (vlib_main_t * vm,
 	      clib_memcpy (&t->i2of, &s0->i2o, sizeof (t->i2of));
 	      clib_memcpy (&t->o2if, &s0->o2i, sizeof (t->o2if));
 	      t->translation_via_i2of = (&s0->i2o == f);
+	      t->tcp_state = s0->tcp_state;
 	    }
 	  else
 	    {
@@ -1170,13 +1152,6 @@ nat44_ed_out2in_slow_path_node_fn_inline (vlib_main_t * vm,
 	  s0 =
 	    pool_elt_at_index (tsm->sessions,
 			       ed_value_get_session_index (&value0));
-
-	  if (s0->tcp_closed_timestamp && now >= s0->tcp_closed_timestamp)
-	    {
-	      nat44_ed_free_session_data (sm, s0, thread_index, 0);
-	      nat_ed_session_delete (sm, s0, thread_index, 1);
-	      s0 = NULL;
-	    }
 	}
 
       if (!s0)
@@ -1264,10 +1239,6 @@ nat44_ed_out2in_slow_path_node_fn_inline (vlib_main_t * vm,
 	  nat44_set_tcp_session_state_o2i (sm, now, s0,
 					   vnet_buffer (b0)->ip.
 					   reass.icmp_type_or_tcp_flags,
-					   vnet_buffer (b0)->ip.
-					   reass.tcp_ack_number,
-					   vnet_buffer (b0)->ip.
-					   reass.tcp_seq_number,
 					   thread_index);
 	}
       else
@@ -1300,6 +1271,7 @@ nat44_ed_out2in_slow_path_node_fn_inline (vlib_main_t * vm,
 	      t->session_index = s0 - tsm->sessions;
 	      clib_memcpy (&t->i2of, &s0->i2o, sizeof (t->i2of));
 	      clib_memcpy (&t->o2if, &s0->o2i, sizeof (t->o2if));
+	      t->tcp_state = s0->tcp_state;
 	    }
 	  else
 	    {