X-Git-Url: https://gerrit.fd.io/r/gitweb?a=blobdiff_plain;f=src%2Fvnet%2Ftcp%2Ftcp_output.c;h=1b9530b4e1a5e73efed3c15fb3135e9957984eef;hb=5e6305fb02ccdfd38c8c5e369a960deaa7602eba;hp=220076057510818478a291578f7a8c6294704aaf;hpb=df36f4963f1a590ce9a02f048507c3d4590580ae;p=vpp.git

diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index 22007605751..1b9530b4e1a 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -55,12 +55,12 @@ format_tcp_tx_trace (u8 * s, va_list * args)
   CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
   CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
   tcp_tx_trace_t *t = va_arg (*args, tcp_tx_trace_t *);
+  tcp_connection_t *tc = &t->tcp_connection;
   u32 indent = format_get_indent (s);
 
-  s = format (s, "%U\n%U%U",
-	      format_tcp_header, &t->tcp_header, 128,
-	      format_white_space, indent,
-	      format_tcp_connection, &t->tcp_connection, 1);
+  s = format (s, "%U state %U\n%U%U", format_tcp_connection_id, tc,
+	      format_tcp_state, tc->state, format_white_space, indent,
+	      format_tcp_header, &t->tcp_header, 128);
 
   return s;
 }
@@ -75,19 +75,6 @@ tcp_window_compute_scale (u32 window)
   return wnd_scale;
 }
 
-/**
- * Update max segment size we're able to process.
- *
- * The value is constrained by our interface's MTU and IP options. It is
- * also what we advertise to our peer.
- */
-void
-tcp_update_rcv_mss (tcp_connection_t * tc)
-{
-  /* TODO find our iface MTU */
-  tc->mss = tcp_cfg.default_mtu - sizeof (tcp_header_t);
-}
-
 /**
  * TCP's initial window
  */
@@ -135,7 +122,10 @@ tcp_update_rcv_wnd (tcp_connection_t * tc)
    */
   available_space = transport_max_rx_enqueue (&tc->connection);
   if (PREDICT_FALSE (available_space < tc->rcv_opts.mss))
-    available_space = 0;
+    {
+      tc->rcv_wnd = 0;
+      return;
+    }
 
   /*
    * Use the above and what we know about what we've previously advertised
@@ -147,7 +137,7 @@ tcp_update_rcv_wnd (tcp_connection_t * tc)
   if (PREDICT_FALSE ((i32) available_space < observed_wnd))
     {
       wnd = clib_max (observed_wnd, 0);
-      TCP_EVT_DBG (TCP_EVT_RCV_WND_SHRUNK, tc, observed_wnd, available_space);
+      TCP_EVT (TCP_EVT_RCV_WND_SHRUNK, tc, observed_wnd, available_space);
     }
   else
     {
@@ -263,16 +253,16 @@ tcp_options_write (u8 * data, tcp_options_t * opts)
 }
 
 static int
-tcp_make_syn_options (tcp_options_t * opts, u8 wnd_scale)
+tcp_make_syn_options (tcp_connection_t * tc, tcp_options_t * opts)
 {
   u8 len = 0;
 
   opts->flags |= TCP_OPTS_FLAG_MSS;
-  opts->mss = tcp_cfg.default_mtu;	/*XXX discover that */
+  opts->mss = tc->mss;
   len += TCP_OPTION_LEN_MSS;
 
   opts->flags |= TCP_OPTS_FLAG_WSCALE;
-  opts->wscale = wnd_scale;
+  opts->wscale = tc->rcv_wscale;
   len += TCP_OPTION_LEN_WINDOW_SCALE;
 
   opts->flags |= TCP_OPTS_FLAG_TSTAMP;
@@ -379,7 +369,7 @@ tcp_make_options (tcp_connection_t * tc, tcp_options_t * opts,
     case TCP_STATE_SYN_RCVD:
       return tcp_make_synack_options (tc, opts);
     case TCP_STATE_SYN_SENT:
-      return tcp_make_syn_options (opts, tc->rcv_wscale);
+      return tcp_make_syn_options (tc, opts);
     default:
       clib_warning ("State not handled! %d", state);
       return 0;
@@ -415,36 +405,16 @@ tcp_update_burst_snd_vars (tcp_connection_t * tc)
 
   tcp_update_rcv_wnd (tc);
 
-  if (tc->flags & TCP_CONN_RATE_SAMPLE)
-    tc->flags |= TCP_CONN_TRACK_BURST;
+  if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+    tcp_bt_check_app_limited (tc);
 
   if (tc->snd_una == tc->snd_nxt)
-    tcp_cc_event (tc, TCP_CC_EVT_START_TX);
-}
-
-void
-tcp_init_mss (tcp_connection_t * tc)
-{
-  u16 default_min_mss = 536;
-  tcp_update_rcv_mss (tc);
-
-  /* TODO cache mss and consider PMTU discovery */
-  tc->snd_mss = clib_min (tc->rcv_opts.mss, tc->mss);
-
-  if (tc->snd_mss < 45)
     {
-      /* Assume that at least the min default mss works */
-      tc->snd_mss = default_min_mss;
-      tc->rcv_opts.mss = default_min_mss;
+      tcp_cc_event (tc, TCP_CC_EVT_START_TX);
+      tcp_connection_tx_pacer_reset (tc, tc->cwnd, TRANSPORT_PACER_MIN_BURST);
     }
-
-  /* We should have enough space for 40 bytes of options */
-  ASSERT (tc->snd_mss > 45);
-
-  /* If we use timestamp option, account for it */
-  if (tcp_opts_tstamp (&tc->rcv_opts))
-    tc->snd_mss -= TCP_OPTION_LEN_TIMESTAMP;
 }
+
 #endif /* CLIB_MARCH_VARIANT */
 
 static void *
@@ -477,6 +447,77 @@ tcp_init_buffer (vlib_main_t * vm, vlib_buffer_t * b)
   return vlib_buffer_make_headroom (b, TRANSPORT_MAX_HDRS_LEN);
 }
 
+
+/* Compute TCP checksum in software when offloading is disabled for a connection */
+u16
+ip6_tcp_compute_checksum_custom (vlib_main_t * vm, vlib_buffer_t * p0,
+				 ip46_address_t * src, ip46_address_t * dst)
+{
+  ip_csum_t sum0;
+  u16 payload_length_host_byte_order;
+  u32 i;
+
+  /* Initialize checksum with ip header. */
+  sum0 = clib_host_to_net_u16 (vlib_buffer_length_in_chain (vm, p0)) +
+    clib_host_to_net_u16 (IP_PROTOCOL_TCP);
+  payload_length_host_byte_order = vlib_buffer_length_in_chain (vm, p0);
+
+  for (i = 0; i < ARRAY_LEN (src->ip6.as_uword); i++)
+    {
+      sum0 = ip_csum_with_carry
+	(sum0, clib_mem_unaligned (&src->ip6.as_uword[i], uword));
+      sum0 = ip_csum_with_carry
+	(sum0, clib_mem_unaligned (&dst->ip6.as_uword[i], uword));
+    }
+
+  return ip_calculate_l4_checksum (vm, p0, sum0,
+				   payload_length_host_byte_order, NULL, 0,
+				   NULL);
+}
+
+u16
+ip4_tcp_compute_checksum_custom (vlib_main_t * vm, vlib_buffer_t * p0,
+				 ip46_address_t * src, ip46_address_t * dst)
+{
+  ip_csum_t sum0;
+  u32 payload_length_host_byte_order;
+
+  payload_length_host_byte_order = vlib_buffer_length_in_chain (vm, p0);
+  sum0 =
+    clib_host_to_net_u32 (payload_length_host_byte_order +
+			  (IP_PROTOCOL_TCP << 16));
+
+  sum0 = ip_csum_with_carry (sum0, clib_mem_unaligned (&src->ip4, u32));
+  sum0 = ip_csum_with_carry (sum0, clib_mem_unaligned (&dst->ip4, u32));
+
+  return ip_calculate_l4_checksum (vm, p0, sum0,
+				   payload_length_host_byte_order, NULL, 0,
+				   NULL);
+}
+
+static inline u16
+tcp_compute_checksum (tcp_connection_t * tc, vlib_buffer_t * b)
+{
+  u16 checksum = 0;
+  if (PREDICT_FALSE (tc->cfg_flags & TCP_CFG_F_NO_CSUM_OFFLOAD))
+    {
+      tcp_worker_ctx_t *wrk = tcp_get_worker (tc->c_thread_index);
+      vlib_main_t *vm = wrk->vm;
+
+      if (tc->c_is_ip4)
+	checksum = ip4_tcp_compute_checksum_custom
+	  (vm, b, &tc->c_lcl_ip, &tc->c_rmt_ip);
+      else
+	checksum = ip6_tcp_compute_checksum_custom
+	  (vm, b, &tc->c_lcl_ip, &tc->c_rmt_ip);
+    }
+  else
+    {
+      b->flags |= VNET_BUFFER_F_OFFLOAD_TCP_CKSUM;
+    }
+  return checksum;
+}
+
 /**
  * Prepare ACK
  */
@@ -499,6 +540,9 @@ tcp_make_ack_i (tcp_connection_t * tc, vlib_buffer_t * b, tcp_state_t state,
 			     tc->rcv_nxt, tcp_hdr_opts_len, flags, wnd);
 
   tcp_options_write ((u8 *) (th + 1), snd_opts);
+
+  th->checksum = tcp_compute_checksum (tc, b);
+
   vnet_buffer (b)->tcp.connection_index = tc->c_c_index;
 
   if (wnd == 0)
@@ -514,7 +558,7 @@ static inline void
 tcp_make_ack (tcp_connection_t * tc, vlib_buffer_t * b)
 {
   tcp_make_ack_i (tc, b, TCP_STATE_ESTABLISHED, TCP_FLAG_ACK);
-  TCP_EVT_DBG (TCP_EVT_ACK_SENT, tc);
+  TCP_EVT (TCP_EVT_ACK_SENT, tc);
   tc->rcv_las = tc->rcv_nxt;
 }
 
@@ -542,7 +586,7 @@ tcp_make_syn (tcp_connection_t * tc, vlib_buffer_t * b)
 
   /* Make and write options */
   clib_memset (&snd_opts, 0, sizeof (snd_opts));
-  tcp_opts_len = tcp_make_syn_options (&snd_opts, tc->rcv_wscale);
+  tcp_opts_len = tcp_make_syn_options (tc, &snd_opts);
   tcp_hdr_opts_len = tcp_opts_len + sizeof (tcp_header_t);
 
   th = vlib_buffer_push_tcp (b, tc->c_lcl_port, tc->c_rmt_port, tc->iss,
@@ -550,6 +594,7 @@ tcp_make_syn (tcp_connection_t * tc, vlib_buffer_t * b)
 			     initial_wnd);
   vnet_buffer (b)->tcp.connection_index = tc->c_c_index;
   tcp_options_write ((u8 *) (th + 1), &snd_opts);
+  th->checksum = tcp_compute_checksum (tc, b);
 }
 
 /**
@@ -574,6 +619,7 @@ tcp_make_synack (tcp_connection_t * tc, vlib_buffer_t * b)
   tcp_options_write ((u8 *) (th + 1), snd_opts);
 
   vnet_buffer (b)->tcp.connection_index = tc->c_c_index;
+  th->checksum = tcp_compute_checksum (tc, b);
 }
 
 always_inline void
@@ -628,51 +674,19 @@ tcp_enqueue_to_ip_lookup (tcp_worker_ctx_t * wrk, vlib_buffer_t * b, u32 bi,
     session_flush_frames_main_thread (wrk->vm);
 }
 
-always_inline void
-tcp_enqueue_to_output_i (tcp_worker_ctx_t * wrk, vlib_buffer_t * b, u32 bi,
-			 u8 is_ip4, u8 flush)
+static void
+tcp_enqueue_to_output (tcp_worker_ctx_t * wrk, vlib_buffer_t * b, u32 bi,
+		       u8 is_ip4)
 {
-  u32 *to_next, next_index;
-  vlib_frame_t *f;
+  session_type_t st;
 
   b->flags |= VNET_BUFFER_F_LOCALLY_ORIGINATED;
   b->error = 0;
 
-  /* Decide where to send the packet */
-  next_index = is_ip4 ? tcp4_output_node.index : tcp6_output_node.index;
-  tcp_trajectory_add_start (b, 2);
-
-  /* Get frame to v4/6 output node */
-  f = wrk->tx_frames[!is_ip4];
-  if (!f)
-    {
-      f = vlib_get_frame_to_node (wrk->vm, next_index);
-      ASSERT (f);
-      wrk->tx_frames[!is_ip4] = f;
-    }
-  to_next = vlib_frame_vector_args (f);
-  to_next[f->n_vectors] = bi;
-  f->n_vectors += 1;
-  if (flush || f->n_vectors == VLIB_FRAME_SIZE)
-    {
-      vlib_put_frame_to_node (wrk->vm, next_index, f);
-      wrk->tx_frames[!is_ip4] = 0;
-    }
-}
-
-static void
-tcp_enqueue_to_output (tcp_worker_ctx_t * wrk, vlib_buffer_t * b, u32 bi,
-		       u8 is_ip4)
-{
-  tcp_enqueue_to_output_i (wrk, b, bi, is_ip4, 0);
+  st = session_type_from_proto_and_ip (TRANSPORT_PROTO_TCP, is_ip4);
+  session_add_pending_tx_buffer (st, wrk->vm->thread_index, bi);
 }
 
-static void
-tcp_enqueue_to_output_now (tcp_worker_ctx_t * wrk, vlib_buffer_t * b, u32 bi,
-			   u8 is_ip4)
-{
-  tcp_enqueue_to_output_i (wrk, b, bi, is_ip4, 1);
-}
 #endif /* CLIB_MARCH_VARIANT */
 
 static int
@@ -819,7 +833,8 @@ tcp_send_reset_w_pkt (tcp_connection_t * tc, vlib_buffer_t * pkt,
     {
       ASSERT ((pkt_ih4->ip_version_and_header_length & 0xF0) == 0x40);
       ih4 = vlib_buffer_push_ip4 (vm, b, &pkt_ih4->dst_address,
-				  &pkt_ih4->src_address, IP_PROTOCOL_TCP, 1);
+				  &pkt_ih4->src_address, IP_PROTOCOL_TCP,
+				  tcp_csum_offload (tc));
       th->checksum = ip4_tcp_udp_compute_checksum (vm, b, ih4);
     }
   else
@@ -827,14 +842,16 @@ tcp_send_reset_w_pkt (tcp_connection_t * tc, vlib_buffer_t * pkt,
       int bogus = ~0;
       ASSERT ((pkt_ih6->ip_version_traffic_class_and_flow_label & 0xF0) ==
 	      0x60);
-      ih6 = vlib_buffer_push_ip6 (vm, b, &pkt_ih6->dst_address,
-				  &pkt_ih6->src_address, IP_PROTOCOL_TCP);
+      ih6 = vlib_buffer_push_ip6_custom (vm, b, &pkt_ih6->dst_address,
+					 &pkt_ih6->src_address,
+					 IP_PROTOCOL_TCP,
+					 tc->ipv6_flow_label);
       th->checksum = ip6_tcp_udp_icmp_compute_checksum (vm, b, ih6, &bogus);
       ASSERT (!bogus);
     }
 
   tcp_enqueue_to_ip_lookup_now (wrk, b, bi, is_ip4, fib_index);
-  TCP_EVT_DBG (TCP_EVT_RST_SENT, tc);
+  TCP_EVT (TCP_EVT_RST_SENT, tc);
   vlib_node_increment_counter (vm, tcp_node_index (output, tc->c_is_ip4),
 			       TCP_ERROR_RST_SENT, 1);
 }
@@ -866,10 +883,11 @@ tcp_send_reset (tcp_connection_t * tc)
 			     tc->rcv_nxt, tcp_hdr_opts_len, flags,
 			     advertise_wnd);
   opts_write_len = tcp_options_write ((u8 *) (th + 1), &tc->snd_opts);
+  th->checksum = tcp_compute_checksum (tc, b);
   ASSERT (opts_write_len == tc->snd_opts_len);
   vnet_buffer (b)->tcp.connection_index = tc->c_c_index;
   tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
-  TCP_EVT_DBG (TCP_EVT_RST_SENT, tc);
+  TCP_EVT (TCP_EVT_RST_SENT, tc);
   vlib_node_increment_counter (vm, tcp_node_index (output, tc->c_is_ip4),
 			       TCP_ERROR_RST_SENT, 1);
 }
@@ -878,24 +896,15 @@ static void
 tcp_push_ip_hdr (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
 		 vlib_buffer_t * b)
 {
-  tcp_header_t *th = vlib_buffer_get_current (b);
-  vlib_main_t *vm = wrk->vm;
   if (tc->c_is_ip4)
     {
-      ip4_header_t *ih;
-      ih = vlib_buffer_push_ip4 (vm, b, &tc->c_lcl_ip4,
-				 &tc->c_rmt_ip4, IP_PROTOCOL_TCP, 1);
-      th->checksum = ip4_tcp_udp_compute_checksum (vm, b, ih);
+      vlib_buffer_push_ip4 (wrk->vm, b, &tc->c_lcl_ip4, &tc->c_rmt_ip4,
+			    IP_PROTOCOL_TCP, tcp_csum_offload (tc));
     }
   else
     {
-      ip6_header_t *ih;
-      int bogus = ~0;
-
-      ih = vlib_buffer_push_ip6 (vm, b, &tc->c_lcl_ip6,
-				 &tc->c_rmt_ip6, IP_PROTOCOL_TCP);
-      th->checksum = ip6_tcp_udp_icmp_compute_checksum (vm, b, ih, &bogus);
-      ASSERT (!bogus);
+      vlib_buffer_push_ip6_custom (wrk->vm, b, &tc->c_lcl_ip6, &tc->c_rmt_ip6,
+				   IP_PROTOCOL_TCP, tc->ipv6_flow_label);
     }
 }
 
@@ -938,7 +947,7 @@ tcp_send_syn (tcp_connection_t * tc)
 
   tcp_push_ip_hdr (wrk, tc, b);
   tcp_enqueue_to_ip_lookup (wrk, b, bi, tc->c_is_ip4, tc->c_fib_index);
-  TCP_EVT_DBG (TCP_EVT_SYN_SENT, tc);
+  TCP_EVT (TCP_EVT_SYN_SENT, tc);
 }
 
 void
@@ -962,22 +971,7 @@ tcp_send_synack (tcp_connection_t * tc)
   tcp_init_buffer (vm, b);
   tcp_make_synack (tc, b);
   tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
-  TCP_EVT_DBG (TCP_EVT_SYNACK_SENT, tc);
-}
-
-/**
- * Flush tx frame populated by retransmits and timer pops
- */
-void
-tcp_flush_frame_to_output (tcp_worker_ctx_t * wrk, u8 is_ip4)
-{
-  if (wrk->tx_frames[!is_ip4])
-    {
-      u32 next_index;
-      next_index = is_ip4 ? tcp4_output_node.index : tcp6_output_node.index;
-      vlib_put_frame_to_node (wrk->vm, next_index, wrk->tx_frames[!is_ip4]);
-      wrk->tx_frames[!is_ip4] = 0;
-    }
+  TCP_EVT (TCP_EVT_SYNACK_SENT, tc);
 }
 
 /**
@@ -1002,8 +996,6 @@ tcp_flush_frame_to_ip_lookup (tcp_worker_ctx_t * wrk, u8 is_ip4)
 void
 tcp_flush_frames_to_output (tcp_worker_ctx_t * wrk)
 {
-  tcp_flush_frame_to_output (wrk, 1);
-  tcp_flush_frame_to_output (wrk, 0);
   tcp_flush_frame_to_ip_lookup (wrk, 1);
   tcp_flush_frame_to_ip_lookup (wrk, 0);
 }
@@ -1036,12 +1028,16 @@ tcp_send_fin (tcp_connection_t * tc)
       return;
     }
 
+  /* If we have non-dupacks programmed, no need to send them */
+  if ((tc->flags & TCP_CONN_SNDACK) && !tc->pending_dupacks)
+    tc->flags &= ~TCP_CONN_SNDACK;
+
   tcp_retransmit_timer_force_update (tc);
   b = vlib_get_buffer (vm, bi);
   tcp_init_buffer (vm, b);
   tcp_make_fin (tc, b);
-  tcp_enqueue_to_output_now (wrk, b, bi, tc->c_is_ip4);
-  TCP_EVT_DBG (TCP_EVT_FIN_SENT, tc);
+  tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
+  TCP_EVT (TCP_EVT_FIN_SENT, tc);
   /* Account for the FIN */
   tc->snd_nxt += 1;
   if (!fin_snt)
@@ -1115,7 +1111,18 @@ tcp_push_hdr_i (tcp_connection_t * tc, vlib_buffer_t * b, u32 snd_nxt,
   tc->bytes_out += data_len;
   tc->data_segs_out += 1;
 
-  TCP_EVT_DBG (TCP_EVT_PKTIZE, tc);
+  th->checksum = tcp_compute_checksum (tc, b);
+
+  TCP_EVT (TCP_EVT_PKTIZE, tc);
+}
+
+always_inline u32
+tcp_buffer_len (vlib_buffer_t * b)
+{
+  u32 data_len = b->current_length;
+  if (PREDICT_FALSE (b->flags & VLIB_BUFFER_NEXT_PRESENT))
+    data_len += b->total_length_not_including_first_buffer;
+  return data_len;
 }
 
 u32
@@ -1123,12 +1130,8 @@ tcp_session_push_header (transport_connection_t * tconn, vlib_buffer_t * b)
 {
   tcp_connection_t *tc = (tcp_connection_t *) tconn;
 
-  if (tc->flags & TCP_CONN_TRACK_BURST)
-    {
-      tcp_bt_check_app_limited (tc);
-      tcp_bt_track_tx (tc);
-      tc->flags &= ~TCP_CONN_TRACK_BURST;
-    }
+  if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+    tcp_bt_track_tx (tc, tcp_buffer_len (b));
 
   tcp_push_hdr_i (tc, b, tc->snd_nxt, /* compute opts */ 0, /* burst */ 1,
 		  /* update_snd_nxt */ 1);
@@ -1192,12 +1195,12 @@ tcp_program_dupack (tcp_connection_t * tc)
 }
 
 void
-tcp_program_fastretransmit (tcp_connection_t * tc)
+tcp_program_retransmit (tcp_connection_t * tc)
 {
-  if (!(tc->flags & TCP_CONN_FRXT_PENDING))
+  if (!(tc->flags & TCP_CONN_RXT_PENDING))
     {
       session_add_self_custom_tx_evt (&tc->connection, 0);
-      tc->flags |= TCP_CONN_FRXT_PENDING;
+      tc->flags |= TCP_CONN_RXT_PENDING;
     }
 }
 
@@ -1207,30 +1210,28 @@ tcp_program_fastretransmit (tcp_connection_t * tc)
  * Sends delayed ACK when timer expires
  */
 void
-tcp_timer_delack_handler (u32 index)
+tcp_timer_delack_handler (u32 index, u32 thread_index)
 {
-  u32 thread_index = vlib_get_thread_index ();
   tcp_connection_t *tc;
 
   tc = tcp_connection_get (index, thread_index);
-  tc->timers[TCP_TIMER_DELACK] = TCP_TIMER_HANDLE_INVALID;
   tcp_send_ack (tc);
 }
 
 /**
- * Send Window Update ACK,
- * ensuring that it will be sent once, if RWND became non-zero,
- * after zero RWND has been advertised in ACK before
+ * Send window update ack
+ *
+ * Ensures that it will be sent only once, after a zero rwnd has been
+ * advertised in a previous ack, and only if rwnd has grown beyond a
+ * configurable value.
  */
 void
 tcp_send_window_update_ack (tcp_connection_t * tc)
 {
-  u32 win;
-
   if (tcp_zero_rwnd_sent (tc))
     {
-      win = tcp_window_to_advertise (tc, tc->state);
-      if (win > 0)
+      tcp_update_rcv_wnd (tc);
+      if (tc->rcv_wnd >= tcp_cfg.rwnd_min_update_ack * tc->snd_mss)
 	{
 	  tcp_zero_rwnd_sent_off (tc);
 	  tcp_program_ack (tc);
@@ -1385,88 +1386,87 @@ tcp_prepare_retransmit_segment (tcp_worker_ctx_t * wrk,
   max_deq_bytes = clib_min (tc->snd_mss, max_deq_bytes);
   max_deq_bytes = clib_min (available_bytes, max_deq_bytes);
 
-  /* Start is beyond snd_congestion */
   start = tc->snd_una + offset;
-  if (seq_geq (start, tc->snd_congestion))
-    return 0;
-
-  /* Don't overshoot snd_congestion */
-  if (seq_gt (start + max_deq_bytes, tc->snd_congestion))
-    {
-      max_deq_bytes = tc->snd_congestion - start;
-      if (max_deq_bytes == 0)
-	return 0;
-    }
+  ASSERT (seq_leq (start + max_deq_bytes, tc->snd_nxt));
 
   n_bytes = tcp_prepare_segment (wrk, tc, offset, max_deq_bytes, b);
   if (!n_bytes)
     return 0;
 
-  if (tcp_in_fastrecovery (tc))
-    {
-      tc->snd_rxt_bytes += n_bytes;
-      if (tc->flags & TCP_CONN_RATE_SAMPLE)
-	tcp_bt_track_rxt (tc, start, start + n_bytes);
-    }
+  tc->snd_rxt_bytes += n_bytes;
+
+  if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+    tcp_bt_track_rxt (tc, start, start + n_bytes);
 
   tc->bytes_retrans += n_bytes;
   tc->segs_retrans += 1;
-  TCP_EVT_DBG (TCP_EVT_CC_RTX, tc, offset, n_bytes);
+  tcp_workerp_stats_inc (wrk, rxt_segs, 1);
+  TCP_EVT (TCP_EVT_CC_RTX, tc, offset, n_bytes);
+
   return n_bytes;
 }
 
+static void
+tcp_check_sack_reneging (tcp_connection_t * tc)
+{
+  sack_scoreboard_t *sb = &tc->sack_sb;
+  sack_scoreboard_hole_t *hole;
+
+  hole = scoreboard_first_hole (sb);
+  if (!sb->is_reneging && (!hole || hole->start == tc->snd_una))
+    return;
+
+  scoreboard_clear_reneging (sb, tc->snd_una, tc->snd_nxt);
+}
+
 /**
  * Reset congestion control, switch cwnd to loss window and try again.
  */
 static void
 tcp_cc_init_rxt_timeout (tcp_connection_t * tc)
 {
-  TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 6);
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 6);
+
   tc->prev_ssthresh = tc->ssthresh;
   tc->prev_cwnd = tc->cwnd;
 
-  /* Clear fast recovery state if needed */
-  if (tcp_in_fastrecovery (tc))
-    tcp_cc_fastrecovery_clear (tc);
+  /* If we entrered loss without fast recovery, notify cc algo of the
+   * congestion event such that it can update ssthresh and its state */
+  if (!tcp_in_fastrecovery (tc))
+    tcp_cc_congestion (tc);
 
-  /* Let cc algo decide loss cwnd and ssthresh */
+  /* Let cc algo decide loss cwnd and ssthresh post unrecovered loss */
   tcp_cc_loss (tc);
 
-  /* Start again from the beginning */
-  tc->snd_congestion = tc->snd_nxt;
-  tc->rcv_dupacks = 0;
   tc->rtt_ts = 0;
   tc->cwnd_acc_bytes = 0;
   tc->tr_occurences += 1;
-  tcp_connection_tx_pacer_reset (tc, tc->cwnd, 2 * tc->snd_mss);
   tcp_recovery_on (tc);
 }
 
 void
-tcp_timer_retransmit_handler (u32 tc_index)
+tcp_timer_retransmit_handler (u32 tc_index, u32 thread_index)
 {
-  u32 thread_index = vlib_get_thread_index ();
   tcp_worker_ctx_t *wrk = tcp_get_worker (thread_index);
   vlib_main_t *vm = wrk->vm;
   tcp_connection_t *tc;
   vlib_buffer_t *b = 0;
   u32 bi, n_bytes;
 
+  tcp_workerp_stats_inc (wrk, tr_events, 1);
   tc = tcp_connection_get (tc_index, thread_index);
 
   /* Note: the connection may have been closed and pool_put */
   if (PREDICT_FALSE (tc == 0 || tc->state == TCP_STATE_SYN_SENT))
     return;
 
-  tc->timers[TCP_TIMER_RETRANSMIT] = TCP_TIMER_HANDLE_INVALID;
-
   /* Wait-close and retransmit could pop at the same time */
   if (tc->state == TCP_STATE_CLOSED)
     return;
 
   if (tc->state >= TCP_STATE_ESTABLISHED)
     {
-      TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 2);
+      TCP_EVT (TCP_EVT_CC_EVT, tc, 2);
 
       /* Lost FIN, retransmit and return */
       if (tc->flags & TCP_CONN_FINSNT)
@@ -1504,35 +1504,23 @@ tcp_timer_retransmit_handler (u32 tc_index)
 	  tcp_send_reset (tc);
 	  tcp_connection_set_state (tc, TCP_STATE_CLOSED);
 	  session_transport_closing_notify (&tc->connection);
+	  session_transport_closed_notify (&tc->connection);
 	  tcp_connection_timers_reset (tc);
 	  tcp_timer_update (tc, TCP_TIMER_WAITCLOSE, tcp_cfg.closewait_time);
+	  tcp_workerp_stats_inc (wrk, tr_abort, 1);
 	  return;
 	}
 
-      /* Increment RTO backoff (also equal to number of retries) and go back
-       * to first un-acked byte  */
-      tc->rto_boff += 1;
+      if (tcp_opts_sack_permitted (&tc->rcv_opts))
+	tcp_check_sack_reneging (tc);
 
-      /* TODO be less aggressive about clearing scoreboard */
-      scoreboard_clear (&tc->sack_sb);
+      /* Update send congestion to make sure that rxt has data to send */
+      tc->snd_congestion = tc->snd_nxt;
 
-      /* First retransmit timeout */
-      if (tc->rto_boff == 1)
-	{
-	  tcp_cc_init_rxt_timeout (tc);
-	  /* Record timestamp. Eifel detection algorithm RFC3522 */
-	  tc->snd_rxt_ts = tcp_tstamp (tc);
-	}
-
-      if (tc->flags & TCP_CONN_RATE_SAMPLE)
-	tcp_bt_flush_samples (tc);
-
-      /* If we've sent beyond snd_congestion, update it */
-      tc->snd_congestion = seq_max (tc->snd_nxt, tc->snd_congestion);
-      tc->snd_nxt = tc->snd_una;
-
-      /* Send one segment. n_bytes may be zero due to buffer shortfall */
-      n_bytes = tcp_prepare_retransmit_segment (wrk, tc, 0, tc->snd_mss, &b);
+      /* Send the first unacked segment. If we're short on buffers, return
+       * as soon as possible */
+      n_bytes = clib_min (tc->snd_mss, tc->snd_nxt - tc->snd_una);
+      n_bytes = tcp_prepare_retransmit_segment (wrk, tc, 0, n_bytes, &b);
       if (!n_bytes)
 	{
 	  tcp_timer_update (tc, TCP_TIMER_RETRANSMIT, 1);
@@ -1544,11 +1532,24 @@ tcp_timer_retransmit_handler (u32 tc_index)
 
       tc->rto = clib_min (tc->rto << 1, TCP_RTO_MAX);
       tcp_retransmit_timer_force_update (tc);
+
+      tc->rto_boff += 1;
+      if (tc->rto_boff == 1)
+	{
+	  tcp_cc_init_rxt_timeout (tc);
+	  /* Record timestamp. Eifel detection algorithm RFC3522 */
+	  tc->snd_rxt_ts = tcp_tstamp (tc);
+	}
+
+      if (tcp_opts_sack_permitted (&tc->rcv_opts))
+	scoreboard_init_rxt (&tc->sack_sb, tc->snd_una + n_bytes);
+
+      tcp_program_retransmit (tc);
     }
   /* Retransmit SYN-ACK */
   else if (tc->state == TCP_STATE_SYN_RCVD)
     {
-      TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 2);
+      TCP_EVT (TCP_EVT_CC_EVT, tc, 2);
 
       tc->rtt_ts = 0;
 
@@ -1558,6 +1559,7 @@ tcp_timer_retransmit_handler (u32 tc_index)
 	  tcp_connection_set_state (tc, TCP_STATE_CLOSED);
 	  tcp_connection_timers_reset (tc);
 	  tcp_timer_update (tc, TCP_TIMER_WAITCLOSE, tcp_cfg.cleanup_time);
+	  tcp_workerp_stats_inc (wrk, tr_abort, 1);
 	  return;
 	}
 
@@ -1576,7 +1578,7 @@ tcp_timer_retransmit_handler (u32 tc_index)
       b = vlib_get_buffer (vm, bi);
       tcp_init_buffer (vm, b);
       tcp_make_synack (tc, b);
-      TCP_EVT_DBG (TCP_EVT_SYN_RXT, tc, 1);
+      TCP_EVT (TCP_EVT_SYN_RXT, tc, 1);
 
       /* Retransmit timer already updated, just enqueue to output */
       tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
@@ -1592,9 +1594,8 @@ tcp_timer_retransmit_handler (u32 tc_index)
  * SYN retransmit timer handler. Active open only.
  */
 void
-tcp_timer_retransmit_syn_handler (u32 tc_index)
+tcp_timer_retransmit_syn_handler (u32 tc_index, u32 thread_index)
 {
-  u32 thread_index = vlib_get_thread_index ();
   tcp_worker_ctx_t *wrk = tcp_get_worker (thread_index);
   vlib_main_t *vm = wrk->vm;
   tcp_connection_t *tc;
@@ -1607,8 +1608,6 @@ tcp_timer_retransmit_syn_handler (u32 tc_index)
   if (PREDICT_FALSE (tc == 0 || tc->state != TCP_STATE_SYN_SENT))
     return;
 
-  tc->timers[TCP_TIMER_RETRANSMIT_SYN] = TCP_TIMER_HANDLE_INVALID;
-
   /* Half-open connection actually moved to established but we were
    * waiting for syn retransmit to pop to call cleanup from the right
    * thread. */
@@ -1619,7 +1618,7 @@ tcp_timer_retransmit_syn_handler (u32 tc_index)
       return;
     }
 
-  TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 2);
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 2);
   tc->rtt_ts = 0;
 
   /* Active open establish timeout */
@@ -1646,7 +1645,7 @@ tcp_timer_retransmit_syn_handler (u32 tc_index)
   tcp_init_buffer (vm, b);
   tcp_make_syn (tc, b);
 
-  TCP_EVT_DBG (TCP_EVT_SYN_RXT, tc, 0);
+  TCP_EVT (TCP_EVT_SYN_RXT, tc, 0);
 
   /* This goes straight to ipx_lookup */
   tcp_push_ip_hdr (wrk, tc, b);
@@ -1661,9 +1660,8 @@ tcp_timer_retransmit_syn_handler (u32 tc_index)
  *
  */
 void
-tcp_timer_persist_handler (u32 index)
+tcp_timer_persist_handler (u32 index, u32 thread_index)
 {
-  u32 thread_index = vlib_get_thread_index ();
   tcp_worker_ctx_t *wrk = tcp_get_worker (thread_index);
   u32 bi, max_snd_bytes, available_bytes, offset;
   tcp_main_t *tm = vnet_get_tcp_main ();
@@ -1677,9 +1675,6 @@ tcp_timer_persist_handler (u32 index)
   if (!tc)
     return;
 
-  /* Make sure timer handle is set to invalid */
-  tc->timers[TCP_TIMER_PERSIST] = TCP_TIMER_HANDLE_INVALID;
-
   /* Problem already solved or worse */
   if (tc->state == TCP_STATE_CLOSED || tc->snd_wnd > tc->snd_mss
       || (tc->flags & TCP_CONN_FINSNT))
@@ -1697,10 +1692,7 @@ tcp_timer_persist_handler (u32 index)
     }
 
   if (available_bytes <= offset)
-    {
-      ASSERT (tcp_timer_is_active (tc, TCP_TIMER_RETRANSMIT));
-      return;
-    }
+    return;
 
   /* Increment RTO backoff */
   tc->rto_boff += 1;
@@ -1728,6 +1720,12 @@ tcp_timer_persist_handler (u32 index)
 			   || tc->snd_nxt == tc->snd_una_max
 			   || tc->rto_boff > 1));
 
+  if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+    {
+      tcp_bt_check_app_limited (tc);
+      tcp_bt_track_tx (tc, n_bytes);
+    }
+
   tcp_push_hdr_i (tc, b, tc->snd_nxt, /* compute opts */ 0,
 		  /* burst */ 0, /* update_snd_nxt */ 1);
   tc->snd_una_max = seq_max (tc->snd_nxt, tc->snd_una_max);
@@ -1748,7 +1746,7 @@ tcp_retransmit_first_unacked (tcp_worker_ctx_t * wrk, tcp_connection_t * tc)
   vlib_buffer_t *b;
   u32 bi, n_bytes;
 
-  TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 1);
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 1);
 
   n_bytes = tcp_prepare_retransmit_segment (wrk, tc, 0, tc->snd_mss, &b);
   if (!n_bytes)
@@ -1761,8 +1759,8 @@ tcp_retransmit_first_unacked (tcp_worker_ctx_t * wrk, tcp_connection_t * tc)
 }
 
 static int
-tcp_fast_retransmit_unsent (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			    u32 burst_size)
+tcp_transmit_unsent (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
+		     u32 burst_size)
 {
   u32 offset, n_segs = 0, n_written, bi, available_wnd;
   vlib_main_t *vm = wrk->vm;
@@ -1772,6 +1770,9 @@ tcp_fast_retransmit_unsent (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
   available_wnd = tc->snd_wnd - offset;
   burst_size = clib_min (burst_size, available_wnd / tc->snd_mss);
 
+  if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+    tcp_bt_check_app_limited (tc);
+
   while (n_segs < burst_size)
     {
       n_written = tcp_prepare_segment (wrk, tc, offset, tc->snd_mss, &b);
@@ -1783,6 +1784,9 @@ tcp_fast_retransmit_unsent (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
       offset += n_written;
       n_segs += 1;
 
+      if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+	tcp_bt_track_tx (tc, n_written);
+
       tc->snd_nxt += n_written;
       tc->snd_una_max = seq_max (tc->snd_nxt, tc->snd_una_max);
     }
@@ -1791,37 +1795,119 @@ done:
   return n_segs;
 }
 
+/**
+ * Estimate send space using proportional rate reduction (RFC6937)
+ */
+int
+tcp_fastrecovery_prr_snd_space (tcp_connection_t * tc)
+{
+  u32 pipe, prr_out;
+  int space;
+
+  pipe = tcp_flight_size (tc);
+  prr_out = tc->snd_rxt_bytes + (tc->snd_nxt - tc->snd_congestion);
+
+  if (pipe > tc->ssthresh)
+    {
+      space = ((int) tc->prr_delivered * ((f64) tc->ssthresh / tc->prev_cwnd))
+	- prr_out;
+    }
+  else
+    {
+      int limit;
+      limit = clib_max ((int) (tc->prr_delivered - prr_out), 0) + tc->snd_mss;
+      space = clib_min (tc->ssthresh - pipe, limit);
+    }
+  space = clib_max (space, prr_out ? 0 : tc->snd_mss);
+  return space;
+}
+
+static inline u8
+tcp_retransmit_should_retry_head (tcp_connection_t * tc,
+				  sack_scoreboard_t * sb)
+{
+  u32 tx_adv_sack = sb->high_sacked - tc->snd_congestion;
+  f64 rr = (f64) tc->ssthresh / tc->prev_cwnd;
+
+  if (tcp_fastrecovery_first (tc))
+    return 1;
+
+  return (tx_adv_sack > (tc->snd_una - tc->prr_start) * rr);
+}
+
+static inline u8
+tcp_max_tx_deq (tcp_connection_t * tc)
+{
+  return (transport_max_tx_dequeue (&tc->connection)
+	  - (tc->snd_nxt - tc->snd_una));
+}
+
 #define scoreboard_rescue_rxt_valid(_sb, _tc)			\
     (seq_geq (_sb->rescue_rxt, _tc->snd_una) 			\
 	&& seq_leq (_sb->rescue_rxt, _tc->snd_congestion))
 
 /**
- * Do fast retransmit with SACKs
+ * Do retransmit with SACKs
  */
-int
-tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			  u32 burst_size)
+static int
+tcp_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
+		     u32 burst_size)
 {
-  u32 n_written = 0, offset, max_bytes, n_segs = 0, n_segs_now;
+  u32 n_written = 0, offset, max_bytes, n_segs = 0;
+  u8 snd_limited = 0, can_rescue = 0;
+  u32 bi, max_deq, burst_bytes;
   sack_scoreboard_hole_t *hole;
   vlib_main_t *vm = wrk->vm;
   vlib_buffer_t *b = 0;
   sack_scoreboard_t *sb;
-  u32 bi, max_deq;
   int snd_space;
-  u8 snd_limited = 0, can_rescue = 0;
 
-  ASSERT (tcp_in_fastrecovery (tc));
+  ASSERT (tcp_in_cong_recovery (tc));
 
-  snd_space = tcp_available_cc_snd_space (tc);
-  if (snd_space < tc->snd_mss)
+  burst_bytes = transport_connection_tx_pacer_burst (&tc->connection);
+  burst_size = clib_min (burst_size, burst_bytes / tc->snd_mss);
+  if (!burst_size)
     {
-      tcp_program_fastretransmit (tc);
+      tcp_program_retransmit (tc);
       return 0;
     }
 
-  TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 0);
+  if (tcp_in_recovery (tc))
+    snd_space = tcp_available_cc_snd_space (tc);
+  else
+    snd_space = tcp_fastrecovery_prr_snd_space (tc);
+
+  if (snd_space < tc->snd_mss)
+    goto done;
+
   sb = &tc->sack_sb;
+
+  /* Check if snd_una is a lost retransmit */
+  if (pool_elts (sb->holes)
+      && seq_gt (sb->high_sacked, tc->snd_congestion)
+      && tc->rxt_head != tc->snd_una
+      && tcp_retransmit_should_retry_head (tc, sb))
+    {
+      max_bytes = clib_min (tc->snd_mss, tc->snd_congestion - tc->snd_una);
+      n_written = tcp_prepare_retransmit_segment (wrk, tc, 0, max_bytes, &b);
+      if (!n_written)
+	{
+	  tcp_program_retransmit (tc);
+	  goto done;
+	}
+      bi = vlib_get_buffer_index (vm, b);
+      tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
+      n_segs = 1;
+
+      tc->rxt_head = tc->snd_una;
+      tc->rxt_delivered += n_written;
+      tc->prr_delivered += n_written;
+      ASSERT (tc->rxt_delivered <= tc->snd_rxt_bytes);
+    }
+
+  tcp_fastrecovery_first_off (tc);
+
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 0);
   hole = scoreboard_get_hole (sb, sb->cur_rxt_hole);
 
   max_deq = transport_max_tx_dequeue (&tc->connection);
@@ -1829,23 +1915,35 @@ tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
 
   while (snd_space > 0 && n_segs < burst_size)
     {
-      hole = scoreboard_next_rxt_hole (sb, hole, max_deq, &can_rescue,
+      hole = scoreboard_next_rxt_hole (sb, hole, max_deq != 0, &can_rescue,
 				       &snd_limited);
       if (!hole)
 	{
-	  if (max_deq)
+	  /* We are out of lost holes to retransmit so send some new data. */
+	  if (max_deq > tc->snd_mss)
 	    {
+	      u32 n_segs_new;
+	      int av_wnd;
+
+	      /* Make sure we don't exceed available window and leave space
+	       * for one more packet, to avoid zero window acks */
+	      av_wnd = (int) tc->snd_wnd - (tc->snd_nxt - tc->snd_una);
+	      av_wnd = clib_max (av_wnd - tc->snd_mss, 0);
+	      snd_space = clib_min (snd_space, av_wnd);
 	      snd_space = clib_min (max_deq, snd_space);
 	      burst_size = clib_min (burst_size - n_segs,
 				     snd_space / tc->snd_mss);
-	      n_segs_now = tcp_fast_retransmit_unsent (wrk, tc, burst_size);
-	      if (max_deq > n_segs_now * tc->snd_mss)
-		tcp_program_fastretransmit (tc);
-	      n_segs += n_segs_now;
+	      burst_size = clib_min (burst_size, TCP_RXT_MAX_BURST);
+	      n_segs_new = tcp_transmit_unsent (wrk, tc, burst_size);
+	      if (max_deq > n_segs_new * tc->snd_mss)
+		tcp_program_retransmit (tc);
+
+	      n_segs += n_segs_new;
 	      goto done;
 	    }
 
-	  if (!can_rescue || scoreboard_rescue_rxt_valid (sb, tc))
+	  if (tcp_in_recovery (tc) || !can_rescue
+	      || scoreboard_rescue_rxt_valid (sb, tc))
 	    break;
 
 	  /* If rescue rxt undefined or less than snd_una then one segment of
@@ -1853,16 +1951,16 @@ tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
 	   * unSACKed sequence number SHOULD be returned, and RescueRxt set to
 	   * RecoveryPoint. HighRxt MUST NOT be updated.
 	   */
-	  max_bytes = clib_min (tc->snd_mss,
-				tc->snd_congestion - tc->snd_una);
+	  hole = scoreboard_last_hole (sb);
+	  max_bytes = clib_min (tc->snd_mss, hole->end - hole->start);
 	  max_bytes = clib_min (max_bytes, snd_space);
-	  offset = tc->snd_congestion - tc->snd_una - max_bytes;
-	  sb->rescue_rxt = tc->snd_congestion;
+	  offset = hole->end - tc->snd_una - max_bytes;
 	  n_written = tcp_prepare_retransmit_segment (wrk, tc, offset,
 						      max_bytes, &b);
 	  if (!n_written)
 	    goto done;
 
+	  sb->rescue_rxt = tc->snd_congestion;
 	  bi = vlib_get_buffer_index (vm, b);
 	  tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
 	  n_segs += 1;
@@ -1887,33 +1985,48 @@ tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
       tcp_enqueue_to_output (wrk, b, bi, tc->c_is_ip4);
 
       sb->high_rxt += n_written;
+      ASSERT (seq_leq (sb->high_rxt, tc->snd_nxt));
+
       snd_space -= n_written;
       n_segs += 1;
     }
 
   if (hole)
-    tcp_program_fastretransmit (tc);
+    tcp_program_retransmit (tc);
 
 done:
+
+  transport_connection_tx_pacer_reset_bucket (&tc->connection, 0);
   return n_segs;
 }
 
 /**
  * Fast retransmit without SACK info
  */
-int
-tcp_fast_retransmit_no_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			     u32 burst_size)
+static int
+tcp_retransmit_no_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
+			u32 burst_size)
 {
-  u32 n_written = 0, offset = 0, bi, max_deq, n_segs_now;
+  u32 n_written = 0, offset = 0, bi, max_deq, n_segs_now, max_bytes;
+  u32 burst_bytes, sent_bytes;
   vlib_main_t *vm = wrk->vm;
   int snd_space, n_segs = 0;
+  u8 cc_limited = 0;
   vlib_buffer_t *b;
 
-  ASSERT (tcp_in_fastrecovery (tc));
-  TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 0);
+  ASSERT (tcp_in_cong_recovery (tc));
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 0);
+
+  burst_bytes = transport_connection_tx_pacer_burst (&tc->connection);
+  burst_size = clib_min (burst_size, burst_bytes / tc->snd_mss);
+  if (!burst_size)
+    {
+      tcp_program_retransmit (tc);
+      return 0;
+    }
 
   snd_space = tcp_available_cc_snd_space (tc);
+  cc_limited = snd_space < burst_bytes;
 
   if (!tcp_fastrecovery_first (tc))
     goto send_unsent;
@@ -1922,8 +2035,12 @@ tcp_fast_retransmit_no_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
    * segment. */
   while (snd_space > 0 && n_segs < burst_size)
     {
-      n_written = tcp_prepare_retransmit_segment (wrk, tc, offset,
-						  tc->snd_mss, &b);
+      max_bytes = clib_min (tc->snd_mss,
+			    tc->snd_congestion - tc->snd_una - offset);
+      if (!max_bytes)
+	break;
+      n_written = tcp_prepare_retransmit_segment (wrk, tc, offset, max_bytes,
+						  &b);
 
       /* Nothing left to retransmit */
       if (n_written == 0)
@@ -1951,28 +2068,20 @@ send_unsent:
     {
       snd_space = clib_min (max_deq, snd_space);
       burst_size = clib_min (burst_size - n_segs, snd_space / tc->snd_mss);
-      n_segs_now = tcp_fast_retransmit_unsent (wrk, tc, burst_size);
-      if (max_deq > n_segs_now * tc->snd_mss)
-	tcp_program_fastretransmit (tc);
+      n_segs_now = tcp_transmit_unsent (wrk, tc, burst_size);
+      if (n_segs_now && max_deq > n_segs_now * tc->snd_mss)
+	tcp_program_retransmit (tc);
       n_segs += n_segs_now;
     }
 
 done:
   tcp_fastrecovery_first_off (tc);
-  return n_segs;
-}
 
-/**
- * Do fast retransmit
- */
-int
-tcp_fast_retransmit (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-		     u32 burst_size)
-{
-  if (tcp_opts_sack_permitted (&tc->rcv_opts))
-    return tcp_fast_retransmit_sack (wrk, tc, burst_size);
-  else
-    return tcp_fast_retransmit_no_sack (wrk, tc, burst_size);
+  sent_bytes = clib_min (n_segs * tc->snd_mss, burst_bytes);
+  sent_bytes = cc_limited ? burst_bytes : sent_bytes;
+  transport_connection_tx_pacer_update_bytes (&tc->connection, sent_bytes);
+
+  return n_segs;
 }
 
 static int
@@ -1982,8 +2091,13 @@ tcp_send_acks (tcp_connection_t * tc, u32 max_burst_size)
 
   if (!tc->pending_dupacks)
     {
-      tcp_send_ack (tc);
-      return 1;
+      if (tcp_in_cong_recovery (tc) || !tcp_max_tx_deq (tc)
+	  || tc->state != TCP_STATE_ESTABLISHED)
+	{
+	  tcp_send_ack (tc);
+	  return 1;
+	}
+      return 0;
     }
 
   /* If we're supposed to send dupacks but have no ooo data
@@ -1991,6 +2105,7 @@ tcp_send_acks (tcp_connection_t * tc, u32 max_burst_size)
   if (!vec_len (tc->snd_sacks))
     {
       tcp_send_ack (tc);
+      tc->pending_dupacks = 0;
       return 1;
     }
 
@@ -2024,25 +2139,21 @@ tcp_send_acks (tcp_connection_t * tc, u32 max_burst_size)
 }
 
 static int
-tcp_do_fastretransmit (tcp_connection_t * tc, u32 max_burst_size)
+tcp_do_retransmit (tcp_connection_t * tc, u32 max_burst_size)
 {
-  u32 n_segs = 0, burst_size, sent_bytes, burst_bytes;
   tcp_worker_ctx_t *wrk;
+  u32 n_segs;
+
+  if (PREDICT_FALSE (tc->state == TCP_STATE_CLOSED))
+    return 0;
 
   wrk = tcp_get_worker (tc->c_thread_index);
-  burst_bytes = transport_connection_tx_pacer_burst (&tc->connection,
-						     wrk->vm->
-						     clib_time.last_cpu_time);
-  burst_size = clib_min (max_burst_size, burst_bytes / tc->snd_mss);
-  if (!burst_size)
-    {
-      tcp_program_fastretransmit (tc);
-      return 0;
-    }
 
-  n_segs = tcp_fast_retransmit (wrk, tc, burst_size);
-  sent_bytes = clib_min (n_segs * tc->snd_mss, burst_bytes);
-  transport_connection_tx_pacer_update_bytes (&tc->connection, sent_bytes);
+  if (tcp_opts_sack_permitted (&tc->rcv_opts))
+    n_segs = tcp_retransmit_sack (wrk, tc, max_burst_size);
+  else
+    n_segs = tcp_retransmit_no_sack (wrk, tc, max_burst_size);
+
   return n_segs;
 }
 
@@ -2052,10 +2163,10 @@ tcp_session_custom_tx (void *conn, u32 max_burst_size)
   tcp_connection_t *tc = (tcp_connection_t *) conn;
   u32 n_segs = 0;
 
-  if (tcp_in_fastrecovery (tc) && (tc->flags & TCP_CONN_FRXT_PENDING))
+  if (tcp_in_cong_recovery (tc) && (tc->flags & TCP_CONN_RXT_PENDING))
     {
-      tc->flags &= ~TCP_CONN_FRXT_PENDING;
-      n_segs = tcp_do_fastretransmit (tc, max_burst_size);
+      tc->flags &= ~TCP_CONN_RXT_PENDING;
+      n_segs = tcp_do_retransmit (tc, max_burst_size);
       max_burst_size -= n_segs;
     }
 
@@ -2116,16 +2227,17 @@ static void
 tcp46_output_trace_frame (vlib_main_t * vm, vlib_node_runtime_t * node,
 			  u32 * to_next, u32 n_bufs)
 {
-  u32 n_trace = vlib_get_trace_count (vm, node);
   tcp_connection_t *tc;
   tcp_tx_trace_t *t;
   vlib_buffer_t *b;
   tcp_header_t *th;
   int i;
 
-  for (i = 0; i < clib_min (n_trace, n_bufs); i++)
+  for (i = 0; i < n_bufs; i++)
     {
       b = vlib_get_buffer (vm, to_next[i]);
+      if (!(b->flags & VLIB_BUFFER_IS_TRACED))
+	continue;
       th = vlib_buffer_get_current (b);
       tc = tcp_connection_get (vnet_buffer (b)->tcp.connection_index,
 			       vm->thread_index);
@@ -2139,27 +2251,39 @@ always_inline void
 tcp_output_push_ip (vlib_main_t * vm, vlib_buffer_t * b0,
 		    tcp_connection_t * tc0, u8 is_ip4)
 {
-  tcp_header_t *th0 = 0;
+  TCP_EVT (TCP_EVT_OUTPUT, tc0,
+	   ((tcp_header_t *) vlib_buffer_get_current (b0))->flags,
+	   b0->current_length);
 
-  th0 = vlib_buffer_get_current (b0);
-  TCP_EVT_DBG (TCP_EVT_OUTPUT, tc0, th0->flags, b0->current_length);
   if (is_ip4)
-    {
-      vlib_buffer_push_ip4 (vm, b0, &tc0->c_lcl_ip4, &tc0->c_rmt_ip4,
-			    IP_PROTOCOL_TCP, 1);
-      b0->flags |= VNET_BUFFER_F_OFFLOAD_TCP_CKSUM;
-      vnet_buffer (b0)->l4_hdr_offset = (u8 *) th0 - b0->data;
-      th0->checksum = 0;
-    }
+    vlib_buffer_push_ip4 (vm, b0, &tc0->c_lcl_ip4, &tc0->c_rmt_ip4,
+			  IP_PROTOCOL_TCP, tcp_csum_offload (tc0));
+  else
+    vlib_buffer_push_ip6_custom (vm, b0, &tc0->c_lcl_ip6, &tc0->c_rmt_ip6,
+				 IP_PROTOCOL_TCP, tc0->ipv6_flow_label);
+}
+
+always_inline void
+tcp_check_if_gso (tcp_connection_t * tc, vlib_buffer_t * b)
+{
+  if (PREDICT_TRUE (!(tc->cfg_flags & TCP_CFG_F_TSO)))
+    return;
+
+  u16 data_len = b->current_length - sizeof (tcp_header_t) - tc->snd_opts_len;
+
+  if (PREDICT_FALSE (b->flags & VLIB_BUFFER_TOTAL_LENGTH_VALID))
+    data_len += b->total_length_not_including_first_buffer;
+
+  if (PREDICT_TRUE (data_len <= tc->snd_mss))
+    return;
   else
     {
-      ip6_header_t *ih0;
-      ih0 = vlib_buffer_push_ip6 (vm, b0, &tc0->c_lcl_ip6,
-				  &tc0->c_rmt_ip6, IP_PROTOCOL_TCP);
-      b0->flags |= VNET_BUFFER_F_OFFLOAD_TCP_CKSUM;
-      vnet_buffer (b0)->l3_hdr_offset = (u8 *) ih0 - b0->data;
-      vnet_buffer (b0)->l4_hdr_offset = (u8 *) th0 - b0->data;
-      th0->checksum = 0;
+      ASSERT ((b->flags & VNET_BUFFER_F_L3_HDR_OFFSET_VALID) != 0);
+      ASSERT ((b->flags & VNET_BUFFER_F_L4_HDR_OFFSET_VALID) != 0);
+      b->flags |= VNET_BUFFER_F_GSO;
+      vnet_buffer2 (b)->gso_l4_hdr_sz =
+	sizeof (tcp_header_t) + tc->snd_opts_len;
+      vnet_buffer2 (b)->gso_size = tc->snd_mss;
     }
 }
 
@@ -2174,6 +2298,10 @@ tcp_output_handle_packet (tcp_connection_t * tc0, vlib_buffer_t * b0,
       *next0 = tc0->next_node_index;
       vnet_buffer (b0)->tcp.next_node_opaque = tc0->next_node_opaque;
     }
+  else
+    {
+      *next0 = TCP_OUTPUT_NEXT_IP_LOOKUP;
+    }
 
   vnet_buffer (b0)->sw_if_index[VLIB_TX] = tc0->c_fib_index;
   vnet_buffer (b0)->sw_if_index[VLIB_RX] = 0;
@@ -2232,18 +2360,49 @@ tcp46_output_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 	CLIB_PREFETCH (b[3]->data, 2 * CLIB_CACHE_LINE_BYTES, STORE);
       }
 
-      next[0] = next[1] = TCP_OUTPUT_NEXT_IP_LOOKUP;
-
       tc0 = tcp_connection_get (vnet_buffer (b[0])->tcp.connection_index,
 				thread_index);
       tc1 = tcp_connection_get (vnet_buffer (b[1])->tcp.connection_index,
 				thread_index);
 
-      tcp_output_push_ip (vm, b[0], tc0, is_ip4);
-      tcp_output_push_ip (vm, b[1], tc1, is_ip4);
+      if (PREDICT_TRUE (!tc0 + !tc1 == 0))
+	{
+	  tcp_output_push_ip (vm, b[0], tc0, is_ip4);
+	  tcp_output_push_ip (vm, b[1], tc1, is_ip4);
 
-      tcp_output_handle_packet (tc0, b[0], error_node, &next[0], is_ip4);
-      tcp_output_handle_packet (tc1, b[1], error_node, &next[1], is_ip4);
+	  tcp_check_if_gso (tc0, b[0]);
+	  tcp_check_if_gso (tc1, b[1]);
+
+	  tcp_output_handle_packet (tc0, b[0], error_node, &next[0], is_ip4);
+	  tcp_output_handle_packet (tc1, b[1], error_node, &next[1], is_ip4);
+	}
+      else
+	{
+	  if (tc0 != 0)
+	    {
+	      tcp_output_push_ip (vm, b[0], tc0, is_ip4);
+	      tcp_check_if_gso (tc0, b[0]);
+	      tcp_output_handle_packet (tc0, b[0], error_node, &next[0],
+					is_ip4);
+	    }
+	  else
+	    {
+	      b[0]->error = error_node->errors[TCP_ERROR_INVALID_CONNECTION];
+	      next[0] = TCP_OUTPUT_NEXT_DROP;
+	    }
+	  if (tc1 != 0)
+	    {
+	      tcp_output_push_ip (vm, b[1], tc1, is_ip4);
+	      tcp_check_if_gso (tc1, b[1]);
+	      tcp_output_handle_packet (tc1, b[1], error_node, &next[1],
+					is_ip4);
+	    }
+	  else
+	    {
+	      b[1]->error = error_node->errors[TCP_ERROR_INVALID_CONNECTION];
+	      next[1] = TCP_OUTPUT_NEXT_DROP;
+	    }
+	}
 
       b += 2;
       next += 2;
@@ -2259,12 +2418,20 @@ tcp46_output_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 	  CLIB_PREFETCH (b[1]->data, 2 * CLIB_CACHE_LINE_BYTES, STORE);
 	}
 
-      next[0] = TCP_OUTPUT_NEXT_IP_LOOKUP;
       tc0 = tcp_connection_get (vnet_buffer (b[0])->tcp.connection_index,
 				thread_index);
 
-      tcp_output_push_ip (vm, b[0], tc0, is_ip4);
-      tcp_output_handle_packet (tc0, b[0], error_node, &next[0], is_ip4);
+      if (PREDICT_TRUE (tc0 != 0))
+	{
+	  tcp_output_push_ip (vm, b[0], tc0, is_ip4);
+	  tcp_check_if_gso (tc0, b[0]);
+	  tcp_output_handle_packet (tc0, b[0], error_node, &next[0], is_ip4);
+	}
+      else
+	{
+	  b[0]->error = error_node->errors[TCP_ERROR_INVALID_CONNECTION];
+	  next[0] = TCP_OUTPUT_NEXT_DROP;
+	}
 
       b += 1;
       next += 1;