Index: sys/netinet/tcp_subr.c
===================================================================
--- sys/netinet/tcp_subr.c
+++ sys/netinet/tcp_subr.c
@@ -3438,6 +3438,13 @@
 		xt->t_sndzerowin = tp->t_sndzerowin;
 		xt->t_sndrexmitpack = tp->t_sndrexmitpack;
 		xt->t_rcvoopack = tp->t_rcvoopack;
+		xt->t_rcv_wnd = tp->rcv_wnd;
+		xt->t_snd_wnd = tp->snd_wnd;
+		xt->t_snd_cwnd = tp->snd_cwnd;
+		xt->t_snd_ssthresh = tp->snd_ssthresh;
+		xt->t_maxseg = tp->t_maxseg;
+		xt->xt_ecn = (tp->t_flags2 & TF2_ECN_PERMIT) ? 1 : 0 +
+			     (tp->t_flags2 & TF2_ACE_PERMIT) ? 2 : 0;
 
 		now = getsbinuptime();
 #define	COPYTIMER(ttt)	do {						\
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -768,7 +768,13 @@
 	int32_t		tt_2msl;		/* (s) */
 	int32_t		tt_delack;		/* (s) */
 	int32_t		t_logstate;		/* (3) */
-	int32_t		spare32[32];
+	uint32_t	t_snd_cwnd;		/* (s) */
+	uint32_t	t_snd_ssthresh;		/* (s) */
+	uint32_t	t_maxseg;		/* (s) */
+	uint32_t	t_rcv_wnd;		/* (s) */
+	uint32_t	t_snd_wnd;		/* (s) */
+	uint32_t	xt_ecn;			/* (s) */
+	int32_t		spare32[26];
 } __aligned(8);
 
 #ifdef _KERNEL
Index: usr.bin/netstat/inet.c
===================================================================
--- usr.bin/netstat/inet.c
+++ usr.bin/netstat/inet.c
@@ -341,9 +341,18 @@
 				xo_emit("  {T:/%8.8s} {T:/%5.5s}",
 				    "flowid", "ftype");
 			}
+			if (cflag) {
+				xo_emit(" {T:/%10.10s} {T:/%10.10s}"
+					" {T:/%5.5s} {T:/%3.3s}",
+					"Cong-win",
+					"ssthresh",
+					"MSS",
+					"ECN");
+			}
 			if (Cflag)
-				xo_emit(" {T:/%-*.*s}", TCP_CA_NAME_MAX,
-				    TCP_CA_NAME_MAX, "CC");
+				xo_emit(" {T:/%-*.*s} {T:/%-*.*s}", TCP_CA_NAME_MAX,
+				    TCP_CA_NAME_MAX, TCP_FUNCTION_NAME_LEN_MAX,
+				    TCP_FUNCTION_NAME_LEN_MAX, "CC", "Stack");
 			if (Pflag)
 				xo_emit(" {T:/%s}", "Log ID");
 			xo_emit("\n");
@@ -518,9 +527,24 @@
 			    inp->inp_flowtype);
 		}
 		if (istcp) {
+			if (cflag)
+				xo_emit(" {:snd-cwnd/%10lu}"
+					" {:snd-ssthresh/%10lu}"
+					" {:t-maxseg/%5u} {:ecn/%3s}",
+					tp->t_snd_cwnd, tp->t_snd_ssthresh,
+					tp->t_maxseg,
+					(tp->t_state >= TCPS_ESTABLISHED ?
+					    (tp->xt_ecn > 0 ?
+						(tp->xt_ecn == 1 ?
+						    "ecn" : "ace")
+						: "off")
+					    : "n/a"));
 			if (Cflag)
-				xo_emit(" {:cc/%-*.*s}", TCP_CA_NAME_MAX,
-				    TCP_CA_NAME_MAX, tp->xt_cc);
+				xo_emit(" {:cc/%-*.*s} {:stack/%-*.*s}",
+				    TCP_CA_NAME_MAX, TCP_CA_NAME_MAX, 
+				    TCP_FUNCTION_NAME_LEN_MAX,
+				    TCP_FUNCTION_NAME_LEN_MAX, 
+				    tp->xt_cc, tp->xt_stack);
 			if (Pflag)
 				xo_emit(" {:log-id/%s}",
 				    tp->xt_logid[0] == '\0' ?
Index: usr.bin/netstat/main.c
===================================================================
--- usr.bin/netstat/main.c
+++ usr.bin/netstat/main.c
@@ -205,7 +205,8 @@
 int	aflag;		/* show all sockets (including servers) */
 static int	Bflag;		/* show information about bpf consumers */
 int	bflag;		/* show i/f total bytes in/out */
-int	Cflag;		/* show congestion control */
+int	cflag;		/* show TCP congestion control info */
+int	Cflag;		/* show congestion control algo and TCP stack */
 int	dflag;		/* show i/f dropped packets */
 int	gflag;		/* show group (multicast) routing or stats */
 int	hflag;		/* show counters in human readable format */
@@ -250,7 +251,7 @@
 	if (argc < 0)
 		exit(EXIT_FAILURE);
 
-	while ((ch = getopt(argc, argv, "46AaBbCdF:f:ghI:iLlM:mN:noPp:Qq:RrSTsuWw:xz"))
+	while ((ch = getopt(argc, argv, "46AaBbCcdF:f:ghI:iLlM:mN:noPp:Qq:RrSTsuWw:xz"))
 	    != -1)
 		switch(ch) {
 		case '4':
@@ -279,6 +280,9 @@
 		case 'b':
 			bflag = 1;
 			break;
+		case 'c':
+			cflag = 1;
+			break;
 		case 'C':
 			Cflag = 1;
 			break;
@@ -874,7 +878,7 @@
 usage(void)
 {
 	(void)xo_error("%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
-"usage: netstat [-46AaLnRSTWx] [-f protocol_family | -p protocol]\n"
+"usage: netstat [-46AaCcLnRSTWx] [-f protocol_family | -p protocol]\n"
 "               [-M core] [-N system]",
 "       netstat -i | -I interface [-46abdhnW] [-f address_family]\n"
 "               [-M core] [-N system]",
Index: usr.bin/netstat/netstat.h
===================================================================
--- usr.bin/netstat/netstat.h
+++ usr.bin/netstat/netstat.h
@@ -41,7 +41,8 @@
 extern int	Aflag;	/* show addresses of protocol control block */
 extern int	aflag;	/* show all sockets (including servers) */
 extern int	bflag;	/* show i/f total bytes in/out */
-extern int	Cflag;	/* show congestion control */
+extern int	cflag;	/* show congestion control stats */
+extern int	Cflag;	/* show congestion control algo and stack */
 extern int	dflag;	/* show i/f dropped packets */
 extern int	gflag;	/* show group (multicast) routing or stats */
 extern int	hflag;	/* show counters in human readable format */
Index: usr.bin/netstat/netstat.1
===================================================================
--- usr.bin/netstat/netstat.1
+++ usr.bin/netstat/netstat.1
@@ -28,7 +28,7 @@
 .\"	@(#)netstat.1	8.8 (Berkeley) 4/18/94
 .\" $FreeBSD$
 .\"
-.Dd September 13, 2020
+.Dd September 21, 2020
 .Dt NETSTAT 1
 .Os
 .Sh NAME
@@ -172,8 +172,10 @@
 .It Fl a
 Show the state of all sockets;
 normally sockets used by server processes are not shown.
+.It Fl c
+Show diagnostic information of the TCP congestion control state.
 .It Fl C
-Show the congestion control of TCP sockets.
+Show the congestion control algorithm and TCP Stack used by a TCP socket.
 .It Fl L
 Show the size of the various listen queues.
 The first count shows the number of unaccepted connections,