Index: head/sys/netinet/tcp_timer.c
===================================================================
--- head/sys/netinet/tcp_timer.c
+++ head/sys/netinet/tcp_timer.c
@@ -664,9 +664,15 @@
 		int isipv6;
 #endif
 
+		/*
+		 * Idea here is that at each stage of mtu probe (usually, 1448
+		 * -> 1188 -> 524) should be given 2 chances to recover before
+		 *  further clamping down. 'tp->t_rxtshift % 2 == 0' should
+		 *  take care of that.
+		 */
 		if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
 		    (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
-		    (tp->t_rxtshift <= 2)) {
+		    (tp->t_rxtshift >= 2 && tp->t_rxtshift % 2 == 0)) {
 			/*
 			 * Enter Path MTU Black-hole Detection mechanism:
 			 * - Disable Path MTU Discovery (IP "DF" bit).
@@ -734,9 +740,11 @@
 			 * with a lowered MTU, maybe this isn't a blackhole and
 			 * we restore the previous MSS and blackhole detection
 			 * flags.
+			 * The limit '6' is determined by giving each probe
+			 * stage (1448, 1188, 524) 2 chances to recover.
 			 */
 			if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
-			    (tp->t_rxtshift > 4)) {
+			    (tp->t_rxtshift > 6)) {
 				tp->t_flags2 |= TF2_PLPMTU_PMTUD;
 				tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
 				optlen = tp->t_maxopd - tp->t_maxseg;