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 November 7, 2022
+.Dd November 9, 2022
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -510,11 +510,28 @@
 .It 3
 Negotiate on incoming connection for Accurate ECN, ECN, or no ECN.
 Outgoing connections will request Accurate ECN and fall back to
-ECN depending on the capabilities of the server.
+ECN depending on the capabilities of the remote host.
 .It 4
 Negotiate on incoming connection for Accurate ECN, ECN, or no ECN.
 Outgoing connections will not request ECN.
 .El
+.It Va ecn.generalized
+Enable sending all segments as ECN capable transport,
+including SYN, SYN/ACK, and retransmissions.
+This may only be enabled when ECN support itself is also active.
+Disabling ECN support will disable this feature automatically.
+Settings:
+.Bl -tag -compact
+.It 0
+Regular RFC3168 operation.
+Send only new data segments as ECN capable transport.
+(default)
+.It 1
+Support generalized ECN (ECN++), and send all segments of an ECN-enabled
+session as ECN capable transport.
+Also control packets to non-established and non-listening ports are
+identically marked, if outgoing sessions would request ECN.
+.El
 .It Va ecn.maxretries
 Number of retries (SYN or SYN/ACK retransmits) before disabling ECN on a
 specific connection.
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
@@ -44,12 +44,11 @@
 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, int);
-uint16_t tcp_ecn_output_syn_sent(struct tcpcb *);
+int	 tcp_ecn_output_syn_sent(struct tcpcb *, uint16_t *);
 int	 tcp_ecn_output_established(struct tcpcb *, uint16_t *, int, bool);
 void	 tcp_ecn_syncache_socket(struct tcpcb *, struct syncache *);
 int	 tcp_ecn_syncache_add(uint16_t, int);
-uint16_t tcp_ecn_syncache_respond(uint16_t, struct syncache *);
-int	 tcp_ecn_get_ace(uint16_t);
+int	 tcp_ecn_syncache_respond(uint16_t *, struct syncache *);
 
 #endif /* _KERNEL */
 
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
@@ -106,8 +106,10 @@
     "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,
+static int sysctl_net_inet_tcp_ecn_enable_check(SYSCTL_HANDLER_ARGS);
+SYSCTL_PROC(_net_inet_tcp_ecn, OID_AUTO, enable,
+    CTLFLAG_VNET | CTLFLAG_RW | CTLTYPE_UINT | CTLFLAG_NEEDGIANT,
+    &VNET_NAME(tcp_do_ecn), 0, &sysctl_net_inet_tcp_ecn_enable_check, "IU",
     "TCP ECN support");
 
 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
@@ -115,13 +117,22 @@
     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_ecn_maxretries), 0,
     "Max retries before giving up on ECN");
 
+VNET_DEFINE(int, tcp_ecn_generalized) = 0;
+static int sysctl_net_inet_tcp_ecn_generalized_check(SYSCTL_HANDLER_ARGS);
+SYSCTL_PROC(_net_inet_tcp_ecn, OID_AUTO, generalized,
+    CTLFLAG_VNET | CTLFLAG_RW | CTLTYPE_UINT | CTLFLAG_NEEDGIANT,
+    &VNET_NAME(tcp_ecn_generalized), 0, &sysctl_net_inet_tcp_ecn_generalized_check, "IU",
+    "Send all packets as ECT");
+
+static inline int
+tcp_ecn_get_ace(uint16_t);
+
 /*
  * 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) ||
@@ -214,6 +225,10 @@
 			break;
 		}
 	}
+	if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
+		if (V_tcp_ecn_generalized)
+			tp->t_flags2 |= TF2_ECN_PLUSPLUS;
+	}
 }
 
 /*
@@ -278,6 +293,10 @@
 			break;
 		}
 	}
+	if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
+		if (V_tcp_ecn_generalized)
+			tp->t_flags2 |= TF2_ECN_PLUSPLUS;
+	}
 }
 
 /*
@@ -363,31 +382,45 @@
 /*
  * Send ECN setup <SYN> packet header flags
  */
-uint16_t
-tcp_ecn_output_syn_sent(struct tcpcb *tp)
+int
+tcp_ecn_output_syn_sent(struct tcpcb *tp, uint16_t *thflags)
 {
-	uint16_t thflags = 0;
-
-	if (V_tcp_do_ecn == 0)
-		return thflags;
-	if (V_tcp_do_ecn == 1) {
-		/* Send a RFC3168 ECN setup <SYN> packet */
+	switch(V_tcp_do_ecn) {
+	case 0: /* No ECN */
+	case 2: /* passive RFC3168 */
+	case 4: /* passice AccECN */
+	default:
+		return IPTOS_ECN_NOTECT;
+		break;
+	case 1: /* Send a RFC3168 ECN setup <SYN> packet */
 		if (tp->t_rxtshift >= 1) {
 			if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
-				thflags = TH_ECE|TH_CWR;
+				*thflags |= TH_ECE|TH_CWR;
+			else
+				return IPTOS_ECN_NOTECT;
 		} else
-			thflags = TH_ECE|TH_CWR;
-	} else
-	if (V_tcp_do_ecn == 3) {
-		/* Send an Accurate ECN setup <SYN> packet */
+			*thflags |= TH_ECE|TH_CWR;
+		break;
+	case 3: /* Send an Accurate ECN setup <SYN> packet */
 		if (tp->t_rxtshift >= 1) {
 			if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
-				thflags = TH_ECE|TH_CWR|TH_AE;
+				*thflags |= TH_ECE|TH_CWR|TH_AE;
+			else
+				return IPTOS_ECN_NOTECT;
 		} else
-			thflags = TH_ECE|TH_CWR|TH_AE;
+			*thflags |= TH_ECE|TH_CWR|TH_AE;
+		break;
 	}
-
-	return thflags;
+	if (V_tcp_ecn_generalized) {
+		if (tp->t_flags2 & TF2_ECN_USE_ECT1) {
+			ipecn = IPTOS_ECN_ECT1;
+			TCPSTAT_INC(tcps_ecn_ect1);
+		} else {
+			ipecn = IPTOS_ECN_ECT0;
+			TCPSTAT_INC(tcps_ecn_ect0);
+		}
+	}
+	return IPTOS_ECN_NOTECT;
 }
 
 /*
@@ -409,8 +442,15 @@
 	newdata = (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
 		    !rxmit &&
 		    !((tp->t_flags & TF_FORCEDATA) && len == 1));
-	/* RFC3168 ECN marking, only new data segments */
-	if (newdata) {
+	/*
+	 * RFC3168 ECN marking for new data segments, or
+	 * for all segments as ECN-capable transport
+	 * when ecn.generalized is set.
+	 */
+	if (newdata ||
+	    tp->t_flags2 & TF2_ECN_PLUSPLUS ||
+	    (tp->t_state == TCPS_SYN_SENT &&
+	     V_tcp_ecn_generalized)) {
 		if (tp->t_flags2 & TF2_ECN_USE_ECT1) {
 			ipecn = IPTOS_ECN_ECT1;
 			TCPSTAT_INC(tcps_ecn_ect1);
@@ -486,6 +526,10 @@
 			break;
 		}
 	}
+	if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
+		if (V_tcp_ecn_generalized)
+			tp->t_flags2 |= TF2_ECN_PLUSPLUS;
+	}
 }
 
 /*
@@ -554,45 +598,62 @@
  * Set up the ECN information for the <SYN,ACK> from
  * syncache information.
  */
-uint16_t
-tcp_ecn_syncache_respond(uint16_t thflags, struct syncache *sc)
+int
+tcp_ecn_syncache_respond(uint16_t *thflags, struct syncache *sc)
 {
-	if ((thflags & TH_SYN) &&
+	int ipecn = IPTOS_ECN_NOTECT;
+
+	if ((*thflags & TH_SYN) &&
 	    (sc->sc_flags & SCF_ECN_MASK)) {
 		switch (sc->sc_flags & SCF_ECN_MASK) {
 		case SCF_ECN:
-			thflags |= (0 | 0 | TH_ECE);
+			*thflags |= (0 | 0 | TH_ECE);
 			TCPSTAT_INC(tcps_ecn_shs);
+			if ((V_tcp_ecn_generalized &&
+				(*thflags & TH_ACK)))
+				ipecn = IPTOS_ECN_ECT0;
 			break;
 		case SCF_ACE_N:
-			thflags |= (0 | TH_CWR | 0);
+			*thflags |= (0 | TH_CWR | 0);
 			TCPSTAT_INC(tcps_ecn_shs);
 			TCPSTAT_INC(tcps_ace_nect);
+			if ((V_tcp_ecn_generalized &&
+				(*thflags & TH_ACK)))
+				ipecn = IPTOS_ECN_ECT0;
 			break;
 		case SCF_ACE_0:
-			thflags |= (TH_AE | 0 | 0);
+			*thflags |= (TH_AE | 0 | 0);
 			TCPSTAT_INC(tcps_ecn_shs);
 			TCPSTAT_INC(tcps_ace_ect0);
+			if ((V_tcp_ecn_generalized &&
+				(*thflags & TH_ACK)))
+				ipecn = IPTOS_ECN_ECT0;
 			break;
 		case SCF_ACE_1:
-			thflags |= (0 | TH_ECE | TH_CWR);
+			*thflags |= (0 | TH_ECE | TH_CWR);
 			TCPSTAT_INC(tcps_ecn_shs);
 			TCPSTAT_INC(tcps_ace_ect1);
+			if ((V_tcp_ecn_generalized &&
+				(*thflags & TH_ACK)))
+				ipecn = IPTOS_ECN_ECT0;
 			break;
 		case SCF_ACE_CE:
-			thflags |= (TH_AE | TH_CWR | 0);
+			*thflags |= (TH_AE | TH_CWR | 0);
 			TCPSTAT_INC(tcps_ecn_shs);
 			TCPSTAT_INC(tcps_ace_ce);
+			if ((V_tcp_ecn_generalized &&
+				(*thflags & TH_ACK)))
+				ipecn = IPTOS_ECN_ECT0;
 			break;
 		/* undefined SCF codepoint */
 		default:
 			break;
 		}
 	}
-	return thflags;
+	return ipecn;
 }
 
-int
+static inline int
 tcp_ecn_get_ace(uint16_t thflags)
 {
 	int ace = 0;
@@ -605,3 +666,45 @@
 		ace += 4;
 	return ace;
 }
+
+static int
+sysctl_net_inet_tcp_ecn_enable_check(SYSCTL_HANDLER_ARGS)
+{
+	uint32_t new;
+	int error;
+
+	new = V_tcp_do_ecn;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 && req->newptr != NULL) {
+		if (new > 4)
+			error = EINVAL;
+		else {
+			V_tcp_do_ecn = new;
+			if (new == 0)
+				V_tcp_ecn_generalized = new;
+		}
+	}
+
+	return (error);
+}
+
+static int
+sysctl_net_inet_tcp_ecn_generalized_check(SYSCTL_HANDLER_ARGS)
+{
+	uint32_t new;
+	int error;
+
+	new = V_tcp_ecn_generalized;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 &&  req->newptr != NULL) {
+		if (new > 1)
+			error = EINVAL;
+		else
+			if (!V_tcp_do_ecn && new == 1)
+				error = EINVAL;
+			else
+				V_tcp_ecn_generalized = new;
+	}
+
+	return (error);
+}
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
@@ -4105,3 +4105,4 @@
 			return (4 * maxseg);
 	}
 }
+
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
@@ -201,6 +201,7 @@
 	int32_t len;
 	uint32_t recwin, sendwin;
 	uint16_t flags;
+	int ect = 0;
 	int off, error = 0;	/* Keep compiler happy */
 	u_int if_hw_tsomaxsegcount = 0;
 	u_int if_hw_tsomaxsegsize = 0;
@@ -1205,26 +1206,27 @@
 	 * RFC 3168.
 	 */
 	if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
-		flags |= tcp_ecn_output_syn_sent(tp);
+		ect = tcp_ecn_output_syn_sent(tp, &flags);
 	}
 	/* Also handle parallel SYN for ECN */
-	if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
-	    (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
-		int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
+	if ((tp->t_flags2 & TF2_ECN_PLUSPLUS) ||
+	    (TCPS_HAVERCVDSYN(tp->t_state) &&
+	    (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)))) {
+		ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
 		if ((tp->t_state == TCPS_SYN_RECEIVED) &&
 		    (tp->t_flags2 & TF2_ECN_SND_ECE))
 			tp->t_flags2 &= ~TF2_ECN_SND_ECE;
+	}
 #ifdef INET6
-		if (isipv6) {
-			ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << 20);
-			ip6->ip6_flow |= htonl(ect << 20);
-		}
-		else
+	if (isipv6) {
+		ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << 20);
+		ip6->ip6_flow |= htonl(ect << 20);
+	}
+	else
 #endif
-		{
-			ip->ip_tos &= ~IPTOS_ECN_MASK;
-			ip->ip_tos |= ect;
-		}
+	{
+		ip->ip_tos &= ~IPTOS_ECN_MASK;
+		ip->ip_tos |= ect;
 	}
 
 	/*
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
@@ -16675,6 +16675,7 @@
 	struct socket *so;
 	uint32_t recwin;
 	uint32_t sb_offset, s_moff = 0;
+	uint8_t ect = 0;
 	int32_t len, error = 0;
 	uint16_t flags;
 	struct mbuf *m, *s_mb = NULL;
@@ -18511,26 +18512,27 @@
 	 * as per RFC 3168.
 	 */
 	if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
-		flags |= tcp_ecn_output_syn_sent(tp);
+		ect |= tcp_ecn_output_syn_sent(tp, &flags);
 	}
 	/* Also handle parallel SYN for ECN */
-	if (TCPS_HAVERCVDSYN(tp->t_state) &&
-	    (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
-		int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
+	if ((tp->t_flags2 & TF2_ECN_PLUSPLUS) ||
+	    (TCPS_HAVERCVDSYN(tp->t_state) &&
+	    (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)))) {
+		ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
 		if ((tp->t_state == TCPS_SYN_RECEIVED) &&
 		    (tp->t_flags2 & TF2_ECN_SND_ECE))
 			tp->t_flags2 &= ~TF2_ECN_SND_ECE;
+	}
 #ifdef INET6
-		if (isipv6) {
-			ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << 20);
-			ip6->ip6_flow |= htonl(ect << 20);
-		}
-		else
+	if (isipv6) {
+		ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << 20);
+		ip6->ip6_flow |= htonl(ect << 20);
+	}
+	else
 #endif
-		{
-			ip->ip_tos &= ~IPTOS_ECN_MASK;
-			ip->ip_tos |= ect;
-		}
+	{
+		ip->ip_tos &= ~IPTOS_ECN_MASK;
+		ip->ip_tos |= ect;
 	}
 	/*
 	 * If we are doing retransmissions, then snd_nxt will not reflect
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
@@ -1991,6 +1991,23 @@
 			optp = (u_char *) (nth + 1);
 			optm = m;
 		}
+	} else {
+		/*
+		 * Send out control packets with same IP ECN header
+		 */
+		if (V_tcp_ecn_generalized &&
+		    ((V_tcp_do_ecn == 1) ||
+		    (V_tcp_do_ecn == 3) ||
+		    ((tp != NULL) &&
+		    (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))))) {
+			if ((tp != NULL) && (tp->t_flags2 & TF2_ECN_USE_ECT1)) {
+				ipecn = IPTOS_ECN_ECT1;
+				TCPSTAT_INC(tcps_ecn_ect1);
+			} else {
+				ipecn = IPTOS_ECN_ECT0;
+				TCPSTAT_INC(tcps_ecn_ect0);
+			}
+		}
 	}
 	if (incl_opts) {
 		/* Timestamps. */
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
@@ -129,7 +129,7 @@
 static void	 syncache_drop(struct syncache *, struct syncache_head *);
 static void	 syncache_free(struct syncache *);
 static void	 syncache_insert(struct syncache *, struct syncache_head *);
-static int	 syncache_respond(struct syncache *, const struct mbuf *, int);
+static int	 syncache_respond(struct syncache *, const struct mbuf *, uint16_t);
 static struct	 socket *syncache_socket(struct syncache *, struct socket *,
 		    struct mbuf *m);
 static void	 syncache_timeout(struct syncache *sc, struct syncache_head *sch,
@@ -1805,14 +1805,15 @@
  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
  */
 static int
-syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags)
+syncache_respond(struct syncache *sc, const struct mbuf *m0, uint16_t flags)
 {
 	struct ip *ip = NULL;
 	struct mbuf *m;
 	struct tcphdr *th = NULL;
 	struct udphdr *udp = NULL;
 	int optlen, error = 0;	/* Make compiler happy */
-	u_int16_t hlen, tlen, mssopt, ulen;
+	uint16_t hlen, tlen, mssopt, ulen;
+	int ect;
 	struct tcpopt to;
 #ifdef INET6
 	struct ip6_hdr *ip6 = NULL;
@@ -1929,7 +1930,17 @@
 	th->th_win = htons(sc->sc_wnd);
 	th->th_urp = 0;
 
-	flags = tcp_ecn_syncache_respond(flags, sc);
+	ect = tcp_ecn_syncache_respond(&flags, sc);
+#ifdef INET6
+	if (sc->sc_inc.inc_flags & INC_ISIPV6)
+		ip6->ip6_flow |= htonl(ect << 20);
+#endif
+#if defined(INET6) && defined(INET)
+	else
+#endif
+#ifdef INET
+		ip->ip_tos |= ect;
+#endif
 	tcp_set_flags(th, flags);
 
 	/* Tack on the TCP options. */
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
@@ -3036,6 +3036,10 @@
 		db_printf("%sTF2_ACE_PERMIT", comma ? ", " : "");
 		comma = 1;
 	}
+	if (t_flags2 & TF2_ECN_PLUSPLUS) {
+		db_printf("%sTF2_ECN_PLUSPLUS", comma ? ", " : "");
+		comma = 1;
+	}
 	if (t_flags2 & TF2_FBYTES_COMPLETE) {
 		db_printf("%sTF2_FBYTES_COMPLETE", comma ? ", " : "");
 		comma = 1;
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
@@ -586,6 +586,7 @@
 #define	TF2_ACE_PERMIT		0x00000100 /* Accurate ECN mode */
 #define	TF2_FBYTES_COMPLETE	0x00000400 /* We have first bytes in and out */
 #define	TF2_ECN_USE_ECT1	0x00000800 /* Use ECT(1) marking on session */
+#define	TF2_ECN_PLUSPLUS	0x00001000 /* ECN++ session */
 
 /*
  * Structure to hold TCP options that are only used during segment
@@ -1002,6 +1003,7 @@
 VNET_DECLARE(int, tcp_do_sack);
 VNET_DECLARE(int, tcp_do_tso);
 VNET_DECLARE(int, tcp_ecn_maxretries);
+VNET_DECLARE(int, tcp_ecn_generalized);
 VNET_DECLARE(int, tcp_initcwnd_segments);
 VNET_DECLARE(int, tcp_insecure_rst);
 VNET_DECLARE(int, tcp_insecure_syn);
@@ -1048,6 +1050,7 @@
 #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_generalized		VNET(tcp_ecn_generalized)
 #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)