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 November 7, 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 */
 
@@ -392,12 +396,12 @@
 	/* Accurate ECN counters. */
 	u_int32_t	tcpi_delivered_ce;
 	u_int32_t	tcpi_received_ce;		/* # of CE marks received */
-	u_int32_t	__tcpi_delivered_e1_bytes;
-	u_int32_t	__tcpi_delivered_e0_bytes;
-	u_int32_t	__tcpi_delivered_ce_bytes;
-	u_int32_t	__tcpi_received_e1_bytes;
-	u_int32_t	__tcpi_received_e0_bytes;
-	u_int32_t	__tcpi_received_ce_bytes;
+	u_int32_t	tcpi_delivered_e1_bytes;
+	u_int32_t	tcpi_delivered_e0_bytes;
+	u_int32_t	tcpi_delivered_ce_bytes;
+	u_int32_t	tcpi_received_e1_bytes;
+	u_int32_t	tcpi_received_e0_bytes;
+	u_int32_t	tcpi_received_ce_bytes;
 
 	/* Padding to grow without breaking ABI. */
 	u_int32_t	__tcpi_pad[19];		/* Padding. */
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
@@ -115,13 +115,17 @@
     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
  */
 void
 tcp_ecn_input_syn_sent(struct tcpcb *tp, uint16_t thflags, int iptos)
 {
-
 	if (V_tcp_do_ecn == 0)
 		return;
 	if ((V_tcp_do_ecn == 1) ||
@@ -291,19 +295,24 @@
 	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_ae.rceb += tlen;
 			TCPSTAT_INC(tcps_ecn_ce);
+			tp->t_rcep++;
 			break;
 		case IPTOS_ECN_ECT0:
+			tp->t_flags2 |= TF2_ACO_E0;
+			tp->t_ae.re0b += tlen;
 			TCPSTAT_INC(tcps_ecn_ect0);
 			break;
 		case IPTOS_ECN_ECT1:
+			tp->t_flags2 |= TF2_ACO_E1;
+			tp->t_ae.re1b += tlen;
 			TCPSTAT_INC(tcps_ecn_ect1);
 			break;
 		}
 
 		if (tp->t_flags2 & TF2_ACE_PERMIT) {
-			if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE)
-				tp->t_rcep += 1;
 			if (tp->t_flags2 & TF2_ECN_PERMIT) {
 				delta_cep = (tcp_ecn_get_ace(thflags) + 8 -
 					    (tp->t_scep & 7)) & 7;
@@ -446,7 +455,6 @@
 		if (tp->t_flags2 & TF2_ECN_SND_ECE)
 			*thflags |= TH_ECE;
 	}
-
 	return ipecn;
 }
 
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
@@ -986,6 +986,8 @@
 	}
 
 	tp = intotcpcb(inp);
+	to.to_ae = &tp->t_ae;
+
 	switch (tp->t_state) {
 	case TCPS_TIME_WAIT:
 		/*
@@ -1550,6 +1552,7 @@
 	inc = &tp->t_inpcb->inp_inc;
 	tp->sackhint.last_sack_ack = 0;
 	sack_changed = 0;
+	to.to_ae = &tp->t_ae;
 	nsegs = max(1, m->m_pkthdr.lro_nsegs);
 
 	NET_EPOCH_ASSERT();
@@ -3556,6 +3559,64 @@
 			to->to_tfo_len = optlen - 2;
 			to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
 			break;
+		case TCPOPT_ACCECN0:
+			if (optlen >= (TCPOLEN_ACCECN_EMPTY +
+					1 * TCPOLEN_ACCECN_COUNTER)) {
+				opt = (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 0)) << 16;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 1)) << 8;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 2)) << 0;
+				opt -= (to->to_ae->se0b & 0xFFFFFF);
+				if (opt > 0)
+					to->to_ae->se0b += opt;
+			}
+			if (optlen >= (TCPOLEN_ACCECN_EMPTY +
+					2 * TCPOLEN_ACCECN_COUNTER)) {
+				opt = (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 3)) << 16;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 4)) << 8;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 5)) << 0;
+				opt -= (to->to_ae->sceb & 0xFFFFFF);
+				if (opt > 0)
+					to->to_ae->sceb += opt;
+			}
+			if (optlen >= (TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER)) {
+				opt = (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 6)) << 16;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 7)) << 8;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 8)) << 0;
+				opt -= (to->to_ae->se1b & 0xFFFFFF);
+				if (opt > 0)
+					to->to_ae->se1b += opt;
+			}
+			break;
+		case TCPOPT_ACCECN1:
+			if (optlen >= (TCPOLEN_ACCECN_EMPTY +
+					1 * TCPOLEN_ACCECN_COUNTER)) {
+				opt = (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 0)) << 16;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 1)) << 8;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 2)) << 0;
+				opt -= (to->to_ae->se1b & 0xFFFFFF);
+				if (opt > 0)
+					to->to_ae->se1b += opt;
+			}
+			if (optlen >= (TCPOLEN_ACCECN_EMPTY +
+					2 * TCPOLEN_ACCECN_COUNTER)) {
+				opt = (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 3)) << 16;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 4)) << 8;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 5)) << 0;
+				opt -= (to->to_ae->sceb & 0xFFFFFF);
+				if (opt > 0)
+					to->to_ae->sceb += opt;
+			}
+			if (optlen >= (TCPOLEN_ACCECN_EMPTY +
+					3 * TCPOLEN_ACCECN_COUNTER)) {
+				opt = (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 6)) << 16;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 7)) << 8;
+				opt |= (uint32_t)(*(uint8_t *)(cp + TCPOLEN_ACCECN_EMPTY + 8)) << 0;
+				opt -= (to->to_ae->se0b & 0xFFFFFF);
+				if (opt > 0)
+					to->to_ae->se0b += opt;
+			}
+			break;
 		default:
 			continue;
 		}
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 +888,35 @@
 		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_ae = &tp->t_ae;
+			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.
@@ -1953,6 +1979,128 @@
 			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_ae->re1b >> 16);
+					*optp++ = (char)(to->to_ae->re1b >> 8);
+					*optp++ = (char)(to->to_ae->re1b);
+					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_ae->re0b >> 16);
+				*optp++ = (char)(to->to_ae->re0b >> 8);
+				*optp++ = (char)(to->to_ae->re0b);
+				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_ae->re1b >> 16);
+					*optp++ = (char)(to->to_ae->re1b >> 8);
+					*optp++ = (char)(to->to_ae->re1b);
+					to->to_flags &= ~TOF_ACCE_E1;
+					*optp++ = (char)(to->to_ae->rceb >> 16);
+					*optp++ = (char)(to->to_ae->rceb >> 8);
+					*optp++ = (char)(to->to_ae->rceb);
+					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_ae->re0b >> 16);
+				*optp++ = (char)(to->to_ae->re0b >> 8);
+				*optp++ = (char)(to->to_ae->re0b);
+				to->to_flags &= ~TOF_ACCE_E0;
+				*optp++ = (char)(to->to_ae->rceb >> 16);
+				*optp++ = (char)(to->to_ae->rceb >> 8);
+				*optp++ = (char)(to->to_ae->rceb);
+				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_ae->re1b >> 16);
+				*optp++ = (char)(to->to_ae->re1b >> 8);
+				*optp++ = (char)(to->to_ae->re1b);
+				to->to_flags &= ~TOF_ACCE_E1;
+				*optp++ = (char)(to->to_ae->rceb >> 16);
+				*optp++ = (char)(to->to_ae->rceb >> 8);
+				*optp++ = (char)(to->to_ae->rceb);
+				to->to_flags &= ~TOF_ACCE_CE;
+				*optp++ = (char)(to->to_ae->re0b >> 16);
+				*optp++ = (char)(to->to_ae->re0b >> 8);
+				*optp++ = (char)(to->to_ae->re0b);
+				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_ae->re0b >> 16);
+				*optp++ = (char)(to->to_ae->re0b >> 8);
+				*optp++ = (char)(to->to_ae->re0b);
+				to->to_flags &= ~TOF_ACCE_E0;
+				*optp++ = (char)(to->to_ae->rceb >> 16);
+				*optp++ = (char)(to->to_ae->rceb >> 8);
+				*optp++ = (char)(to->to_ae->rceb);
+				to->to_flags &= ~TOF_ACCE_CE;
+				*optp++ = (char)(to->to_ae->re1b >> 16);
+				*optp++ = (char)(to->to_ae->re1b >> 8);
+				*optp++ = (char)(to->to_ae->re1b);
+				to->to_flags &= ~TOF_ACCE_E1;
+				continue;
+			}
+			}
 		default:
 			panic("%s: unknown TCP option type", __func__);
 			break;
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
@@ -1801,7 +1801,6 @@
 #ifdef INVARIANTS
 	int thflags = tcp_get_flags(th);
 #endif
-
 	KASSERT(tp != NULL || m != NULL, ("tcp_respond: tp and m both NULL"));
 	NET_EPOCH_ASSERT();
 
@@ -2008,9 +2007,26 @@
 		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_ae = &tp->t_ae;
+			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 +2347,14 @@
 	tcp_log_tcpcbinit(tp);
 #endif
 	tp->t_pacing_rate = -1;
+	if (V_tcp_do_lrd)
+		tp->t_flags |= TF_LRD;
+	tp->t_ae.re0b = 1;
+	tp->t_ae.re1b = 1;
+	tp->t_ae.rceb = 0;
+	tp->t_ae.se0b = 1;
+	tp->t_ae.se1b = 1;
+	tp->t_ae.sceb = 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);
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
@@ -1817,6 +1817,7 @@
 #ifdef INET6
 	struct ip6_hdr *ip6 = NULL;
 #endif
+	struct accecn ae;
 
 	NET_EPOCH_ASSERT();
 
@@ -1956,6 +1957,20 @@
 				/* 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;
+			ae.re0b = 1;
+			ae.re1b = 1;
+			ae.rceb = 0;
+			to.to_ae = &ae;
 		}
 		if (sc->sc_flags & SCF_TIMESTAMP) {
 			to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -1644,15 +1644,23 @@
 	 * AccECN related counters.
 	 */
 	if ((tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) ==
-	    (TF2_ECN_PERMIT | TF2_ACE_PERMIT))
+	    (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
 		/*
 		 * Internal counter starts at 5 for AccECN
 		 * but 0 for RFC3168 ECN.
 		 */
 		ti->tcpi_delivered_ce = tp->t_scep - 5;
-	else
+		ti->tcpi_received_ce = tp->t_rcep - 5;
+	} else {
 		ti->tcpi_delivered_ce = tp->t_scep;
-	ti->tcpi_received_ce = tp->t_rcep;
+		ti->tcpi_received_ce = tp->t_rcep;
+	}
+	ti->tcpi_received_e0_bytes = tp->t_ae.re0b - 1;
+	ti->tcpi_received_e1_bytes = tp->t_ae.re1b - 1;
+	ti->tcpi_received_ce_bytes = tp->t_ae.rceb;
+	ti->tcpi_delivered_e0_bytes = tp->t_ae.se0b - 1;
+	ti->tcpi_delivered_e1_bytes = tp->t_ae.se1b - 1;
+	ti->tcpi_delivered_ce_bytes = tp->t_ae.sceb;
 }
 
 /*
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
@@ -120,6 +120,15 @@
 	uint32_t	prr_out;	/* Bytes sent during IN_RECOVERY */
 };
 
+struct accecn {
+	uint32_t	re0b;		/* Number of ECT0 marked data bytes */
+	uint32_t	re1b;		/* Number of ECT1 marked data bytes */
+	uint32_t	rceb;		/* Number of CE marked data bytes */
+	uint32_t	se0b;		/* Synced number of delivered ECT0 bytes */
+	uint32_t	se1b;		/* Synced number of delivered ECT1 bytes */
+	uint32_t	sceb;		/* Synced number of delivered CE bytes */
+};
+
 #define SEGQ_EMPTY(tp) TAILQ_EMPTY(&(tp)->t_segq)
 
 STAILQ_HEAD(tcp_log_stailq, tcp_log_mem);
@@ -251,6 +260,7 @@
 	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 */
+	struct accecn	t_ae;		/* AccECN related byte counters */
 	int64_t	t_pacing_rate;		/* bytes / sec, -1 => unlimited */
 	struct tcp_log_stailq t_logs;	/* Log buffer */
 	struct tcp_log_id_node *t_lin;
@@ -577,7 +587,10 @@
 #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.
@@ -588,14 +601,21 @@
  */
 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 */
@@ -605,7 +625,8 @@
 	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 */
+	struct accecn	*to_ae;		/* pointer to AccECN byte counters */
+	u_int32_t       to_spare;       /* UTO */
 };
 
 /*
@@ -996,6 +1017,7 @@
 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);
@@ -1042,6 +1064,7 @@
 #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)