diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -34,7 +34,7 @@
 .\"     From: @(#)tcp.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd October 7, 2022
+.Dd October 11, 2022
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -520,6 +520,9 @@
 specific connection.
 This is needed to help with connection establishment
 when a broken firewall is in the network path.
+.It Va ecn.option
+Reflect back the number of received bytes with a particular ECN marking
+by using the Accurate ECN TCP option on each outgoing packet.
 .It Va fast_finwait2_recycle
 Recycle
 .Tn TCP
diff --git a/sys/netinet/tcp.h b/sys/netinet/tcp.h
--- a/sys/netinet/tcp.h
+++ b/sys/netinet/tcp.h
@@ -104,6 +104,10 @@
 #define	   TCPOLEN_SIGNATURE		18
 #define	TCPOPT_FAST_OPEN	34
 #define	   TCPOLEN_FAST_OPEN_EMPTY	2
+#define	TCPOPT_ACCECN0		0xAC
+#define	TCPOPT_ACCECN1		0XAE
+#define	   TCPOLEN_ACCECN_EMPTY		2
+#define	   TCPOLEN_ACCECN_COUNTER	3
 
 #define	MAX_TCPOPTLEN		40	/* Absolute maximum TCP options len */
 
diff --git a/sys/netinet/tcp_ecn.h b/sys/netinet/tcp_ecn.h
--- a/sys/netinet/tcp_ecn.h
+++ b/sys/netinet/tcp_ecn.h
@@ -43,7 +43,7 @@
 
 void	 tcp_ecn_input_syn_sent(struct tcpcb *, uint16_t, int);
 void	 tcp_ecn_input_parallel_syn(struct tcpcb *, uint16_t, int);
-int	 tcp_ecn_input_segment(struct tcpcb *, uint16_t, int);
+int	 tcp_ecn_input_segment(struct tcpcb *, uint16_t, int, int);
 uint16_t tcp_ecn_output_syn_sent(struct tcpcb *);
 int	 tcp_ecn_output_established(struct tcpcb *, uint16_t *, int, bool);
 void	 tcp_ecn_syncache_socket(struct tcpcb *, struct syncache *);
diff --git a/sys/netinet/tcp_ecn.c b/sys/netinet/tcp_ecn.c
--- a/sys/netinet/tcp_ecn.c
+++ b/sys/netinet/tcp_ecn.c
@@ -101,6 +101,24 @@
 #include <netinet/tcpip.h>
 #include <netinet/tcp_ecn.h>
 
+static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn,
+    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
+    "TCP ECN");
+
+VNET_DEFINE(int, tcp_do_ecn) = 2;
+SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable,
+    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_do_ecn), 0,
+    "TCP ECN support");
+
+VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
+SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries,
+    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_ecn_maxretries), 0,
+    "Max retries before giving up on ECN");
+
+VNET_DEFINE(int, tcp_ecn_option) = 0;
+SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, option,
+    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_ecn_option), 0,
+    "Use AccECN TCP option");
 
 /*
  * Process incoming SYN,ACK packet
@@ -108,7 +126,7 @@
 void
 tcp_ecn_input_syn_sent(struct tcpcb *tp, uint16_t thflags, int iptos)
 {
-
+log(2, "%s:%d\t th:%03x ecn:%02x\n", __func__, __LINE__, thflags, iptos);
 	if (V_tcp_do_ecn == 0)
 		return;
 	if ((V_tcp_do_ecn == 1) ||
@@ -209,6 +227,7 @@
 void
 tcp_ecn_input_parallel_syn(struct tcpcb *tp, uint16_t thflags, int iptos)
 {
+log(2, "%s:%d\t th:%03x ecn:%02x\n", __func__, __LINE__, thflags, iptos);
 	if (thflags & TH_ACK)
 		return;
 	if (V_tcp_do_ecn == 0)
@@ -271,19 +290,26 @@
  * TCP ECN processing.
  */
 int
-tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int iptos)
+tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int tlen, int iptos)
 {
+log(2, "%s:%d\t th:%03x ecn:%02x\n", __func__, __LINE__, thflags, iptos);
 	int delta_ace = 0;
 
 	if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
 		switch (iptos & IPTOS_ECN_MASK) {
 		case IPTOS_ECN_CE:
+			tp->t_flags2 |= TF2_ACO_CE;
+			tp->t_rceb += tlen;
 			TCPSTAT_INC(tcps_ecn_ce);
 			break;
 		case IPTOS_ECN_ECT0:
+			tp->t_flags2 |= TF2_ACO_E0;
+			tp->t_re0b += tlen;
 			TCPSTAT_INC(tcps_ecn_ect0);
 			break;
 		case IPTOS_ECN_ECT1:
+			tp->t_flags2 |= TF2_ACO_E1;
+			tp->t_re1b += tlen;
 			TCPSTAT_INC(tcps_ecn_ect1);
 			break;
 		}
@@ -348,6 +374,7 @@
 uint16_t
 tcp_ecn_output_syn_sent(struct tcpcb *tp)
 {
+log(2, "%s:%d\t\n", __func__, __LINE__);
 	uint16_t thflags = 0;
 
 	if (V_tcp_do_ecn == 0)
@@ -379,6 +406,8 @@
 int
 tcp_ecn_output_established(struct tcpcb *tp, uint16_t *thflags, int len, bool rxmit)
 {
+log(2, "%s:%d\t th:%03x\n", __func__, __LINE__, *thflags);
+
 	int ipecn = IPTOS_ECN_NOTECT;
 	bool newdata;
 
@@ -400,6 +429,11 @@
 	 * Reply with proper ECN notifications.
 	 */
 	if (tp->t_flags2 & TF2_ACE_PERMIT) {
+	        log(2, "%s:%d\t ace:%d ecn:%d rcep:%d\n",
+	    	    __func__, __LINE__, 
+	    	    (tp->t_flags2 & TF2_ACE_PERMIT) ? 1 : 0, 
+	    	    (tp->t_flags2 & TF2_ECN_PERMIT) ? 1:0, 
+	    	    tp->t_rcep);
 		*thflags &= ~(TH_AE|TH_CWR|TH_ECE);
 		if (tp->t_rcep & 0x01)
 			*thflags |= TH_ECE;
@@ -439,6 +473,8 @@
 void
 tcp_ecn_syncache_socket(struct tcpcb *tp, struct syncache *sc)
 {
+log(2, "%s:%d\t tf2:%03x sc:%02x\n", __func__, __LINE__, tp->t_flags2, sc->sc_flags);
+
 	if (sc->sc_flags & SCF_ECN_MASK) {
 		switch (sc->sc_flags & SCF_ECN_MASK) {
 		case SCF_ECN:
@@ -472,6 +508,8 @@
 int
 tcp_ecn_syncache_add(uint16_t thflags, int iptos)
 {
+log(2, "%s:%d\t th:%03x ecn:%02x\n", __func__, __LINE__, thflags, iptos);
+
 	int scflags = 0;
 
 	switch (thflags & (TH_AE|TH_CWR|TH_ECE)) {
@@ -534,6 +572,7 @@
 uint16_t
 tcp_ecn_syncache_respond(uint16_t thflags, struct syncache *sc)
 {
+log(2, "%s:%d\t th:%03x sc:%02x\n", __func__, __LINE__, thflags, sc->sc_flags);
 	if ((thflags & TH_SYN) &&
 	    (sc->sc_flags & SCF_ECN_MASK)) {
 		switch (sc->sc_flags & SCF_ECN_MASK) {
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -204,20 +204,6 @@
     &VNET_NAME(tcp_abc_l_var), 2,
     "Cap the max cwnd increment during slow-start to this number of segments");
 
-static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn,
-    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
-    "TCP ECN");
-
-VNET_DEFINE(int, tcp_do_ecn) = 2;
-SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(tcp_do_ecn), 0,
-    "TCP ECN support");
-
-VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
-SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(tcp_ecn_maxretries), 0,
-    "Max retries before giving up on ECN");
-
 VNET_DEFINE(int, tcp_insecure_syn) = 0;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_insecure_syn), 0,
@@ -1634,7 +1620,7 @@
 	/*
 	 * TCP ECN processing.
 	 */
-	if (tcp_ecn_input_segment(tp, thflags, iptos))
+	if (tcp_ecn_input_segment(tp, thflags, tlen, iptos))
 		cc_cong_signal(tp, th, CC_ECN);
 
 	/*
@@ -2235,6 +2221,7 @@
 	 */
 	if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
 	    tp->t_state != TCPS_SYN_RECEIVED) {
+		log(2, "%s:%d\n", __func__, __LINE__);
 		TCPSTAT_INC(tcps_badsyn);
 		if (V_tcp_insecure_syn &&
 		    SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -888,9 +888,37 @@
 		if (tp->t_flags & TF_SIGNATURE)
 			to.to_flags |= TOF_SIGNATURE;
 #endif /* TCP_SIGNATURE */
-
+		/*
+		 * AccECN option
+		 * Don't send on <SYN>, only on <SYN,ACK> or
+		 * when doing an AccECN session
+		 */
+		if (V_tcp_ecn_option &&
+		    ((V_tcp_do_ecn == 3) || (V_tcp_do_ecn == 4)) &&
+		    ((tp->t_flags2 & TF2_ACE_PERMIT) ||
+		    ((flags & TH_SYN) && (flags & TH_ACK)))) {
+			to.to_flags |= TOF_ACCECNOPT;
+			to.to_ee0b = tp->t_re0b;
+			to.to_ee1b = tp->t_re1b;
+			to.to_eceb = tp->t_rceb;
+			to.to_flags |= ((tp->t_flags2 & TF2_ACO_E0) ? TOF_ACCE_E0 : 0) |
+					  ((tp->t_flags2 & TF2_ACO_E1) ? TOF_ACCE_E1 : 0) |
+					  ((tp->t_flags2 & TF2_ACO_CE) ? TOF_ACCE_CE : 0);
+			if (flags & TH_SYN)
+				to.to_flags |= TOF_ACCE_SYN;
+			if (tp->t_flags & TF_ACKNOW)
+				to.to_flags |= TOF_ACCE_ACKNOW;
+		}
 		/* Processing the options. */
 		hdrlen += optlen = tcp_addoptions(&to, opt);
+		if (to.to_flags & TOF_ACCECNOPT) {
+			if ((to.to_flags & TOF_ACCE_E0) == 0)
+				tp->t_flags2 &= ~TF2_ACO_E0;
+			if ((to.to_flags & TOF_ACCE_E1) == 0)
+				tp->t_flags2 &= ~TF2_ACO_E1;
+			if ((to.to_flags & TOF_ACCE_CE) == 0)
+				tp->t_flags2 &= ~TF2_ACO_CE;
+		}
 		/*
 		 * If we wanted a TFO option to be added, but it was unable
 		 * to fit, ensure no data is sent.
@@ -1776,6 +1804,8 @@
 	int tt;
 	int maxunacktime;
 
+	log(2, "%s:%d\n", __func__, __LINE__);
+
 	tp->t_flags &= ~TF_PREVVALID;
 	if (tcp_timer_active(tp, TT_REXMT))
 		panic("tcp_setpersist: retransmit pending");
@@ -1953,6 +1983,128 @@
 			optlen += total_len;
 			break;
 			}
+		case TOF_ACCECNOPT:
+			{
+			int max_len = TCP_MAXOLEN - optlen;
+			if (max_len < TCPOLEN_ACCECN_EMPTY) {
+				to->to_flags &= ~TOF_ACCECNOPT;
+				continue;
+			}
+			if (max_len < (TCPOLEN_ACCECN_EMPTY +
+					1 * TCPOLEN_ACCECN_COUNTER)) {
+				if (to->to_flags & TOF_ACCE_SYN) {
+					*optp++ = TCPOPT_ACCECN0;
+					optlen += TCPOLEN_ACCECN_EMPTY;
+					*optp++ = TCPOLEN_ACCECN_EMPTY;
+					continue;
+				} else {
+					to->to_flags &= ~TOF_ACCECNOPT;
+					continue;
+				}
+			}
+			if (max_len < (TCPOLEN_ACCECN_EMPTY +
+					2 * TCPOLEN_ACCECN_COUNTER)) {
+				if (to->to_flags & TOF_ACCE_E1) {
+					*optp++ = TCPOPT_ACCECN1;
+					*optp++ = TCPOLEN_ACCECN_EMPTY +
+						TCPOLEN_ACCECN_COUNTER;
+					optlen += TCPOLEN_ACCECN_EMPTY +
+						TCPOLEN_ACCECN_COUNTER;
+					*optp++ = (char)(to->to_ee1b >> 16);
+					*optp++ = (char)(to->to_ee1b >> 8);
+					*optp++ = (char)(to->to_ee1b);
+					to->to_flags &= ~TOF_ACCE_E1;
+					continue;
+				}
+				*optp++ = TCPOPT_ACCECN0;
+				*optp++ = TCPOLEN_ACCECN_EMPTY +
+					TCPOLEN_ACCECN_COUNTER;
+				optlen += TCPOLEN_ACCECN_EMPTY +
+					TCPOLEN_ACCECN_COUNTER;
+				*optp++ = (char)(to->to_ee0b >> 16);
+				*optp++ = (char)(to->to_ee0b >> 8);
+				*optp++ = (char)(to->to_ee0b);
+				to->to_flags &= ~TOF_ACCE_E0;
+				continue;
+			}
+			if (max_len < (TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER)) {
+				if (to->to_flags & TOF_ACCE_E1) {
+					*optp++ = TCPOPT_ACCECN1;
+					*optp++ = TCPOLEN_ACCECN_EMPTY +
+						2 * TCPOLEN_ACCECN_COUNTER;
+					optlen += TCPOLEN_ACCECN_EMPTY +
+						2 * TCPOLEN_ACCECN_COUNTER;
+					*optp++ = (char)(to->to_ee1b >> 16);
+					*optp++ = (char)(to->to_ee1b >> 8);
+					*optp++ = (char)(to->to_ee1b);
+					to->to_flags &= ~TOF_ACCE_E1;
+					*optp++ = (char)(to->to_eceb >> 16);
+					*optp++ = (char)(to->to_eceb >> 8);
+					*optp++ = (char)(to->to_eceb);
+					to->to_flags &= ~TOF_ACCE_CE;
+					continue;
+				}
+				*optp++ = TCPOPT_ACCECN0;
+				*optp++ = TCPOLEN_ACCECN_EMPTY +
+					2 * TCPOLEN_ACCECN_COUNTER;
+				optlen += TCPOLEN_ACCECN_EMPTY +
+					2 * TCPOLEN_ACCECN_COUNTER;
+				*optp++ = (char)(to->to_ee0b >> 16);
+				*optp++ = (char)(to->to_ee0b >> 8);
+				*optp++ = (char)(to->to_ee0b);
+				to->to_flags &= ~TOF_ACCE_E0;
+				*optp++ = (char)(to->to_eceb >> 16);
+				*optp++ = (char)(to->to_eceb >> 8);
+				*optp++ = (char)(to->to_eceb);
+				to->to_flags &= ~TOF_ACCE_CE;
+				continue;
+			}
+			/*
+			 * TCP option sufficient to hold full AccECN option
+			 * but only send changed counters normally,
+			 * full counters on ACKNOW
+			 */
+			if (to->to_flags & TOF_ACCE_E1) {
+				*optp++ = TCPOPT_ACCECN1;
+				*optp++ = TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER;
+				optlen += TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER;
+				*optp++ = (char)(to->to_ee1b >> 16);
+				*optp++ = (char)(to->to_ee1b >> 8);
+				*optp++ = (char)(to->to_ee1b);
+				to->to_flags &= ~TOF_ACCE_E1;
+				*optp++ = (char)(to->to_eceb >> 16);
+				*optp++ = (char)(to->to_eceb >> 8);
+				*optp++ = (char)(to->to_eceb);
+				to->to_flags &= ~TOF_ACCE_CE;
+				*optp++ = (char)(to->to_ee0b >> 16);
+				*optp++ = (char)(to->to_ee0b >> 8);
+				*optp++ = (char)(to->to_ee0b);
+				to->to_flags &= ~TOF_ACCE_E0;
+				continue;
+			} else {
+				*optp++ = TCPOPT_ACCECN0;
+				*optp++ = TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER;
+				optlen += TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER;
+				*optp++ = (char)(to->to_ee0b >> 16);
+				*optp++ = (char)(to->to_ee0b >> 8);
+				*optp++ = (char)(to->to_ee0b);
+				to->to_flags &= ~TOF_ACCE_E0;
+				*optp++ = (char)(to->to_eceb >> 16);
+				*optp++ = (char)(to->to_eceb >> 8);
+				*optp++ = (char)(to->to_eceb);
+				to->to_flags &= ~TOF_ACCE_CE;
+				*optp++ = (char)(to->to_ee1b >> 16);
+				*optp++ = (char)(to->to_ee1b >> 8);
+				*optp++ = (char)(to->to_ee1b);
+				to->to_flags &= ~TOF_ACCE_E1;
+				continue;
+			}
+			}
 		default:
 			panic("%s: unknown TCP option type", __func__);
 			break;
diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c
--- a/sys/netinet/tcp_stacks/rack.c
+++ b/sys/netinet/tcp_stacks/rack.c
@@ -13528,8 +13528,8 @@
 			rack_cc_after_idle(rack, tp);
 		}
 		tp->t_rcvtime = ticks;
-		/* Now what about ECN? */
-		if (tcp_ecn_input_segment(tp, ae->flags, ae->codepoint))
+		/* Now what about ECN of a chain of pure ACKs? */
+		if (tcp_ecn_input_segment(tp, ae->flags, 0, ae->codepoint))
 			rack_cong_signal(tp, CC_ECN, ae->ack, __LINE__);
 #ifdef TCP_ACCOUNTING
 		/* Count for the specific type of ack in */
@@ -14318,7 +14318,7 @@
 	 * TCP ECN processing. XXXJTL: If we ever use ECN, we need to move
 	 * this to occur after we've validated the segment.
 	 */
-	if (tcp_ecn_input_segment(tp, thflags, iptos))
+	if (tcp_ecn_input_segment(tp, thflags, tlen, iptos))
 		rack_cong_signal(tp, CC_ECN, th->th_ack, __LINE__);
 
 	/*
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -1801,6 +1801,7 @@
 #ifdef INVARIANTS
 	int thflags = tcp_get_flags(th);
 #endif
+	log(2, "%s:%d\n", __func__, __LINE__);
 
 	KASSERT(tp != NULL || m != NULL, ("tcp_respond: tp and m both NULL"));
 	NET_EPOCH_ASSERT();
@@ -2008,9 +2009,28 @@
 		if (tp->t_flags & TF_SIGNATURE)
 			to.to_flags |= TOF_SIGNATURE;
 #endif
+		/* AccECN option */
+		if (V_tcp_ecn_option &&
+		    ((V_tcp_do_ecn == 3) || (V_tcp_do_ecn == 4)) &&
+		    (tp->t_flags2 & TF2_ACE_PERMIT)) {
+			to.to_flags |= TOF_ACCECNOPT;
+			to.to_ee0b = tp->t_re0b;
+			to.to_ee1b = tp->t_re1b;
+			to.to_eceb = tp->t_rceb;
+			to.to_flags |= ((tp->t_flags2 & TF2_ACO_E0) ? TOF_ACCE_E0 : 0) |
+					((tp->t_flags2 & TF2_ACO_E1) ? TOF_ACCE_E1 : 0) |
+					((tp->t_flags2 & TF2_ACO_CE) ? TOF_ACCE_CE : 0);
+		}
 		/* Add the options. */
 		tlen += optlen = tcp_addoptions(&to, optp);
-
+		if (to.to_flags & TOF_ACCECNOPT) {
+			if ((to.to_flags & TOF_ACCE_E0) == 0)
+				tp->t_flags2 &= ~TF2_ACO_E0;
+			if ((to.to_flags & TOF_ACCE_E1) == 0)
+				tp->t_flags2 &= ~TF2_ACO_E1;
+			if ((to.to_flags & TOF_ACCE_CE) == 0)
+				tp->t_flags2 &= ~TF2_ACO_CE;
+		}
 		/* Update m_len in the correct mbuf. */
 		optm->m_len += optlen;
 	} else
@@ -2331,6 +2351,11 @@
 	tcp_log_tcpcbinit(tp);
 #endif
 	tp->t_pacing_rate = -1;
+	if (V_tcp_do_lrd)
+		tp->t_flags |= TF_LRD;
+	tp->t_re0b = 1;
+	tp->t_re1b = 1;
+	tp->t_rceb = 0;
 	if (tp->t_fb->tfb_tcp_fb_init) {
 		if ((*tp->t_fb->tfb_tcp_fb_init)(tp)) {
 			refcount_release(&tp->t_fb->tfb_refcnt);
@@ -2343,8 +2368,6 @@
 	if (V_tcp_perconn_stats_enable == 1)
 		tp->t_stats = stats_blob_alloc(V_tcp_perconn_stats_dflt_tpl, 0);
 #endif
-	if (V_tcp_do_lrd)
-		tp->t_flags |= TF_LRD;
 	return (tp);		/* XXX */
 }
 
diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -475,6 +475,8 @@
 	int tick = ticks;
 	char *s;
 	bool paused;
+	
+	log(2, "%s:%d\t\n", __func__, __LINE__);
 
 	CURVNET_SET(sch->sch_sc->vnet);
 
@@ -615,6 +617,7 @@
 	struct syncache *sc;
 	struct syncache_head *sch;
 	char *s = NULL;
+	log(2, "%s:%d\t\n", __func__, __LINE__);
 
 	if (syncache_cookiesonly())
 		return;
@@ -1412,6 +1415,8 @@
 	int tfo_cookie_valid = 0;
 	int tfo_response_cookie_valid = 0;
 	bool locked;
+	log(2, "%s:%d\t\n", __func__, __LINE__);
+
 
 	INP_RLOCK_ASSERT(inp);			/* listen socket */
 	KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
@@ -1817,6 +1822,7 @@
 #ifdef INET6
 	struct ip6_hdr *ip6 = NULL;
 #endif
+	log(2, "%s.%d\n", __func__, __LINE__);
 
 	NET_EPOCH_ASSERT();
 
@@ -1956,6 +1962,19 @@
 				/* don't send cookie again when retransmitting response */
 				sc->sc_tfo_cookie = NULL;
 			}
+			if (V_tcp_ecn_option)
+				to.to_flags |= TOF_ACCE_SYN;
+		}
+		if (V_tcp_ecn_option &&
+		    (sc->sc_flags & SCF_ECN_MASK) &&
+		    ((sc->sc_flags & SCF_ECN_MASK) != SCF_ECN)) {
+			to.to_flags |= TOF_ACCECNOPT;
+			to.to_flags |= TOF_ACCE_E0 |
+					TOF_ACCE_E1 |
+					TOF_ACCE_CE;
+			to.to_ee0b = 1;
+			to.to_ee1b = 1;
+			to.to_eceb = 0;
 		}
 		if (sc->sc_flags & SCF_TIMESTAMP) {
 			to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c
--- a/sys/netinet/tcp_timer.c
+++ b/sys/netinet/tcp_timer.c
@@ -321,6 +321,8 @@
 #ifdef TCPDEBUG
 	int ostate;
 
+	log(2, "%s:%d\n", __func__, __LINE__);
+
 	ostate = tp->t_state;
 #endif
 	inp = tp->t_inpcb;
@@ -396,6 +398,8 @@
 #ifdef TCPDEBUG
 	int ostate;
 
+	log(2, "%s:%d\n", __func__, __LINE__);
+
 	ostate = tp->t_state;
 #endif
 	inp = tp->t_inpcb;
@@ -540,6 +544,8 @@
 #ifdef TCPDEBUG
 	int ostate;
 
+	log(2, "%s:%d\n", __func__, __LINE__);
+
 	ostate = tp->t_state;
 #endif
 	inp = tp->t_inpcb;
@@ -624,6 +630,8 @@
 #ifdef TCPDEBUG
 	int ostate;
 
+	log(2, "%s:%d\n", __func__, __LINE__);
+
 	ostate = tp->t_state;
 #endif
 	inp = tp->t_inpcb;
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -251,6 +251,9 @@
 	int	t_loglimit;		/* Maximum number of log entries */
 	uint32_t t_rcep;		/* Number of received CE marked pkts */
 	uint32_t t_scep;		/* Synced number of delivered CE pkts */
+	uint32_t t_re0b;		/* Number of ECT0 marked data bytes */
+	uint32_t t_re1b;		/* Number of ECT1 marked data bytes */
+	uint32_t t_rceb;		/* Number of CE marked data bytes */
 	int64_t	t_pacing_rate;		/* bytes / sec, -1 => unlimited */
 	struct tcp_log_stailq t_logs;	/* Log buffer */
 	struct tcp_log_id_node *t_lin;
@@ -570,7 +573,10 @@
 #define	TF2_ECN_SND_CWR		0x00000040 /* ECN CWR in queue */
 #define	TF2_ECN_SND_ECE		0x00000080 /* ECN ECE in queue */
 #define	TF2_ACE_PERMIT		0x00000100 /* Accurate ECN mode */
-#define TF2_FBYTES_COMPLETE	0x00000400 /* We have first bytes in and out */
+#define	TF2_ACO_E0		0x00000200 /* EE0 counter changed */
+#define	TF2_ACO_E1		0x00000400 /* EE1 counter changed */
+#define	TF2_ACO_CE		0x00000800 /* ECE counter changed */
+#define	TF2_FBYTES_COMPLETE	0x00001000 /* We have first bytes in and out */
 /*
  * Structure to hold TCP options that are only used during segment
  * processing (in tcp_input), but not held in the tcpcb.
@@ -581,14 +587,21 @@
  */
 struct tcpopt {
 	u_int32_t	to_flags;	/* which options are present */
-#define	TOF_MSS		0x0001		/* maximum segment size */
-#define	TOF_SCALE	0x0002		/* window scaling */
-#define	TOF_SACKPERM	0x0004		/* SACK permitted */
-#define	TOF_TS		0x0010		/* timestamp */
-#define	TOF_SIGNATURE	0x0040		/* TCP-MD5 signature option (RFC2385) */
-#define	TOF_SACK	0x0080		/* Peer sent SACK option */
-#define	TOF_FASTOPEN	0x0100		/* TCP Fast Open (TFO) cookie */
-#define	TOF_MAXOPT	0x0200
+#define	TOF_MSS		0x00000001	/* maximum segment size */
+#define	TOF_SCALE	0x00000002	/* window scaling */
+#define	TOF_SACKPERM	0x00000004	/* SACK permitted */
+#define	TOF_TS		0x00000010	/* timestamp */
+#define	TOF_SIGNATURE	0x00000040	/* TCP-MD5 signature option (RFC2385) */
+#define	TOF_SACK	0x00000080	/* Peer sent SACK option */
+#define	TOF_FASTOPEN	0x00000100	/* TCP Fast Open (TFO) cookie */
+#define	TOF_ACCECNOPT	0x00000200	/* AccECN Option */
+#define	TOF_MAXOPT	0x00000400
+					/* Keep internal flags above TOF_MAXOPT */
+#define	TOF_ACCE_SYN	0x80000000	/* send empty option */
+#define	TOF_ACCE_CE	0x40000000	/* CE counter changed */
+#define	TOF_ACCE_E0	0x20000000	/* E0 counter changed */
+#define	TOF_ACCE_E1	0x10000000	/* E1 counter changed */
+#define	TOF_ACCE_ACKNOW	0x08000000	/* send full option */
 	u_int32_t	to_tsval;	/* new timestamp */
 	u_int32_t	to_tsecr;	/* reflected timestamp */
 	u_char		*to_sacks;	/* pointer to the first SACK blocks */
@@ -598,7 +611,10 @@
 	u_int8_t	to_wscale;	/* window scaling */
 	u_int8_t	to_nsacks;	/* number of SACK blocks */
 	u_int8_t	to_tfo_len;	/* TFO cookie length */
-	u_int32_t	to_spare;	/* UTO */
+	u_int32_t	to_ee0b;	/* AccECN E0 marked bytes */
+	u_int32_t	to_ee1b;	/* AccECN E1 marked bytes */
+	u_int32_t	to_eceb;	/* AccECN CE marked bytes */
+	u_int32_t       to_spare;       /* UTO */
 };
 
 /*
@@ -989,6 +1005,7 @@
 VNET_DECLARE(int, tcp_do_sack);
 VNET_DECLARE(int, tcp_do_tso);
 VNET_DECLARE(int, tcp_ecn_maxretries);
+VNET_DECLARE(int, tcp_ecn_option);
 VNET_DECLARE(int, tcp_initcwnd_segments);
 VNET_DECLARE(int, tcp_insecure_rst);
 VNET_DECLARE(int, tcp_insecure_syn);
@@ -1035,6 +1052,7 @@
 #define	V_tcp_do_sack			VNET(tcp_do_sack)
 #define	V_tcp_do_tso			VNET(tcp_do_tso)
 #define	V_tcp_ecn_maxretries		VNET(tcp_ecn_maxretries)
+#define	V_tcp_ecn_option		VNET(tcp_ecn_option)
 #define	V_tcp_initcwnd_segments		VNET(tcp_initcwnd_segments)
 #define	V_tcp_insecure_rst		VNET(tcp_insecure_rst)
 #define	V_tcp_insecure_syn		VNET(tcp_insecure_syn)