Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -2436,7 +2436,9 @@
 		hhook_run_tcp_est_in(tp, th, &to);
 
 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
-			if (tlen == 0 && tiwin == tp->snd_wnd) {
+			if ((tlen == 0 && tiwin == tp->snd_wnd) ||
+			    ((tp->t_flags & TF_SACK_PERMIT) &&
+			    tp->sackhint.change_in_sacked_bytes)) {
 				/*
 				 * If this is the first time we've seen a
 				 * FIN from the remote, this is not a
@@ -2478,8 +2480,13 @@
 				 * When using TCP ECN, notify the peer that
 				 * we reduced the cwnd.
 				 */
-				if (!tcp_timer_active(tp, TT_REXMT) ||
-				    th->th_ack != tp->snd_una)
+				/*
+				 * Old acks should not be affecting t_dupacks
+				 * counting so ignore them.
+				 */
+				if (th->th_ack != tp->snd_una)
+					break;
+				else if (!tcp_timer_active(tp, TT_REXMT))
 					tp->t_dupacks = 0;
 				else if (++tp->t_dupacks > tcprexmtthresh ||
 				     IN_FASTRECOVERY(tp->t_flags)) {
@@ -2608,8 +2615,7 @@
 					tp->snd_cwnd = oldcwnd;
 					goto drop;
 				}
-			} else
-				tp->t_dupacks = 0;
+			}
 			break;
 		}
 
Index: sys/netinet/tcp_sack.c
===================================================================
--- sys/netinet/tcp_sack.c
+++ sys/netinet/tcp_sack.c
@@ -351,11 +351,12 @@
 {
 	struct sackhole *cur, *temp;
 	struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
-	int i, j, num_sack_blks;
+	int i, j, num_sack_blks, old_sacked_bytes;
 
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
 	num_sack_blks = 0;
+	old_sacked_bytes = 0;
 	/*
 	 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 	 * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
@@ -369,6 +370,7 @@
 	 * received new blocks from the other side.
 	 */
 	if (to->to_flags & TOF_SACK) {
+		old_sacked_bytes = tp->sackhint.sacked_bytes;
 		tp->sackhint.sacked_bytes = 0;	/* reset */
 		for (i = 0; i < to->to_nsacks; i++) {
 			bcopy((to->to_sacks + i * TCPOLEN_SACK),
@@ -387,12 +389,19 @@
 			}
 		}
 	}
+
+	/* Find the change in sacked bytes */
+	tp->sackhint.change_in_sacked_bytes = tp->sackhint.sacked_bytes -
+						old_sacked_bytes;
 	/*
 	 * Return if SND.UNA is not advanced and no valid SACK block is
 	 * received.
 	 */
-	if (num_sack_blks == 0)
+	if (num_sack_blks == 0) {
+		/* XXXHP: Unsure if this is really needed */
+		tp->sackhint.change_in_sacked_bytes = 0;
 		return;
+	}
 
 	/*
 	 * Sort the SACK blocks so we can update the scoreboard with just one
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -78,6 +78,11 @@
 					 * Total sacked bytes reported by the
 					 * receiver via sack option
 					 */
+	int             change_in_sacked_bytes;
+					/*
+					 * (Signed) Difference of data in
+					 * scoreboard due to the current ACK
+					 */
 	uint64_t	_pad[1];	/* TBD */
 };