Index: sys/netinet/cc/cc_cubic.c
===================================================================
--- sys/netinet/cc/cc_cubic.c
+++ sys/netinet/cc/cc_cubic.c
@@ -317,7 +317,7 @@
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_rfc6675_pipe)
+		if (V_tcp_do_rfc6675)
 			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 		else
 			pipe = CCV(ccv, snd_max) - ccv->curack;
Index: sys/netinet/cc/cc_htcp.c
===================================================================
--- sys/netinet/cc/cc_htcp.c
+++ sys/netinet/cc/cc_htcp.c
@@ -360,7 +360,7 @@
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_rfc6675_pipe)
+		if (V_tcp_do_rfc6675)
 			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 		else
 			pipe = CCV(ccv, snd_max) - ccv->curack;
Index: sys/netinet/cc/cc_newreno.c
===================================================================
--- sys/netinet/cc/cc_newreno.c
+++ sys/netinet/cc/cc_newreno.c
@@ -227,7 +227,7 @@
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_rfc6675_pipe)
+		if (V_tcp_do_rfc6675)
 			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 		else
 			pipe = CCV(ccv, snd_max) - ccv->curack;
Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -152,10 +152,10 @@
     &VNET_NAME(drop_synfin), 0,
     "Drop TCP packets with SYN+FIN set");
 
-VNET_DEFINE(int, tcp_do_rfc6675_pipe) = 0;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc6675_pipe, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(tcp_do_rfc6675_pipe), 0,
-    "Use calculated pipe/in-flight bytes per RFC 6675");
+VNET_DEFINE(int, tcp_do_rfc6675) = 0;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc6675, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(tcp_do_rfc6675), 0,
+    "Enable (partial) RFC 6675 support for pipe, cwnd and ssthresh calculations");
 
 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
 #define	V_tcp_do_rfc3042	VNET(tcp_do_rfc3042)
@@ -2582,7 +2582,7 @@
 						 * we have less than 1/2 the original window's
 						 * worth of data in flight.
 						 */
-						if (V_tcp_do_rfc6675_pipe)
+						if (V_tcp_do_rfc6675)
 							awnd = tcp_compute_pipe(tp);
 						else
 							awnd = (tp->snd_nxt - tp->snd_fack) +
@@ -2628,7 +2628,18 @@
 						TCPSTAT_INC(
 						    tcps_sack_recovery_episode);
 						tp->sack_newdata = tp->snd_nxt;
-						tp->snd_cwnd = maxseg;
+						/*
+						 * As per RFC6675,
+						 * ssthresh = cwnd = pipe / 2
+						 */
+						if (V_tcp_do_rfc6675) {
+							int pipe;
+							pipe = tcp_compute_pipe(tp);
+							tp->snd_ssthresh =
+							    tp->snd_cwnd = pipe / 2;
+						} else
+							tp->snd_cwnd = maxseg;
+
 						(void) tp->t_fb->tfb_tcp_output(tp);
 						goto drop;
 					}
Index: sys/netinet/tcp_stacks/fastpath.c
===================================================================
--- sys/netinet/tcp_stacks/fastpath.c
+++ sys/netinet/tcp_stacks/fastpath.c
@@ -1097,7 +1097,7 @@
 						 * we have less than 1/2 the original window's
 						 * worth of data in flight.
 						 */
-						if (V_tcp_do_rfc6675_pipe)
+						if (V_tcp_do_rfc6675)
 							awnd = tcp_compute_pipe(tp);
 						else
 							awnd = (tp->snd_nxt - tp->snd_fack) +
@@ -1143,7 +1143,17 @@
 						TCPSTAT_INC(
 						    tcps_sack_recovery_episode);
 						tp->sack_newdata = tp->snd_nxt;
-						tp->snd_cwnd = tp->t_maxseg;
+						/*
+						 * As per RFC6675,
+						 * ssthresh = cwnd = pipe / 2
+						 */
+						if (V_tcp_do_rfc6675) {
+							int pipe;
+							pipe = tcp_compute_pipe(tp);
+							tp->snd_ssthresh =
+							    tp->snd_cwnd = pipe / 2;
+						} else
+							tp->snd_cwnd = tp->t_maxseg;
 						(void) tp->t_fb->tfb_tcp_output(tp);
 						goto drop;
 					}
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -739,8 +739,8 @@
 VNET_DECLARE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST + 1]);
 #define	V_tcp_hhh		VNET(tcp_hhh)
 
-VNET_DECLARE(int, tcp_do_rfc6675_pipe);
-#define V_tcp_do_rfc6675_pipe	VNET(tcp_do_rfc6675_pipe)
+VNET_DECLARE(int, tcp_do_rfc6675);
+#define V_tcp_do_rfc6675	VNET(tcp_do_rfc6675)
 
 int	 tcp_addoptions(struct tcpopt *, u_char *);
 int	 tcp_ccalgounload(struct cc_algo *unload_algo);