Index: head/share/man/man4/tcp.4
===================================================================
--- head/share/man/man4/tcp.4
+++ head/share/man/man4/tcp.4
@@ -34,7 +34,7 @@
 .\"     From: @(#)tcp.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd August 6, 2018
+.Dd March 23, 2019
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -459,7 +459,7 @@
 the system-calculated automatic limit and the user-specified
 .Va reass.maxqueuelen
 limit.
-.It Va rexmit_min , rexmit_slop
+.It Va rexmit_initial , rexmit_min , rexmit_slop
 Adjust the retransmit timer calculation for
 .Tn TCP .
 The slop is
@@ -481,6 +481,7 @@
 For this reason, we use 200ms of slop and a near-0
 minimum, which gives us an effective minimum of 200ms (similar to
 .Tn Linux ) .
+The initial value is used before an RTT measurement has been performed.
 .It Va initcwnd_segments
 Enable the ability to specify initial congestion window in number of segments.
 The default value is 10 as suggested by RFC 6928.
Index: head/sys/netinet/tcp_subr.c
===================================================================
--- head/sys/netinet/tcp_subr.c
+++ head/sys/netinet/tcp_subr.c
@@ -1065,6 +1065,9 @@
 	tcp_keepintvl = TCPTV_KEEPINTVL;
 	tcp_maxpersistidle = TCPTV_KEEP_IDLE;
 	tcp_msl = TCPTV_MSL;
+	tcp_rexmit_initial = TCPTV_RTOBASE;
+	if (tcp_rexmit_initial < 1)
+		tcp_rexmit_initial = 1;
 	tcp_rexmit_min = TCPTV_MIN;
 	if (tcp_rexmit_min < 1)
 		tcp_rexmit_min = 1;
@@ -1645,9 +1648,9 @@
 	 * reasonable initial retransmit time.
 	 */
 	tp->t_srtt = TCPTV_SRTTBASE;
-	tp->t_rttvar = ((TCPTV_RTOBASE - TCPTV_SRTTBASE) << TCP_RTTVAR_SHIFT) / 4;
+	tp->t_rttvar = ((tcp_rexmit_initial - TCPTV_SRTTBASE) << TCP_RTTVAR_SHIFT) / 4;
 	tp->t_rttmin = tcp_rexmit_min;
-	tp->t_rxtcur = TCPTV_RTOBASE;
+	tp->t_rxtcur = tcp_rexmit_initial;
 	tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
 	tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
 	tp->t_rcvtime = ticks;
Index: head/sys/netinet/tcp_syncache.c
===================================================================
--- head/sys/netinet/tcp_syncache.c
+++ head/sys/netinet/tcp_syncache.c
@@ -155,10 +155,10 @@
 /*
  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  * 3 retransmits corresponds to a timeout with default values of
- * TCPTV_RTOBASE * (             1 +
- *                  tcp_backoff[1] +
- *                  tcp_backoff[2] +
- *                  tcp_backoff[3]) + 3 * tcp_rexmit_slop,
+ * tcp_rexmit_initial * (             1 +
+ *                       tcp_backoff[1] +
+ *                       tcp_backoff[2] +
+ *                       tcp_backoff[3]) + 3 * tcp_rexmit_slop,
  * 1000 ms * (1 + 2 + 4 + 8) +  3 * 200 ms = 15600 ms,
  * the odds are that the user has given up attempting to connect by then.
  */
@@ -424,9 +424,10 @@
 	int rexmt;
 
 	if (sc->sc_rxmits == 0)
-		rexmt = TCPTV_RTOBASE;
+		rexmt = tcp_rexmit_initial;
 	else
-		TCPT_RANGESET(rexmt, TCPTV_RTOBASE * tcp_backoff[sc->sc_rxmits],
+		TCPT_RANGESET(rexmt,
+		    tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits],
 		    tcp_rexmit_min, TCPTV_REXMTMAX);
 	sc->sc_rxttime = ticks + rexmt;
 	sc->sc_rxmits++;
Index: head/sys/netinet/tcp_timer.h
===================================================================
--- head/sys/netinet/tcp_timer.h
+++ head/sys/netinet/tcp_timer.h
@@ -194,6 +194,7 @@
 extern int tcp_keepcnt;			/* number of keepalives */
 extern int tcp_delacktime;		/* time before sending a delayed ACK */
 extern int tcp_maxpersistidle;
+extern int tcp_rexmit_initial;
 extern int tcp_rexmit_min;
 extern int tcp_rexmit_slop;
 extern int tcp_msl;
Index: head/sys/netinet/tcp_timer.c
===================================================================
--- head/sys/netinet/tcp_timer.c
+++ head/sys/netinet/tcp_timer.c
@@ -110,6 +110,11 @@
 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
 
+int	tcp_rexmit_initial;
+SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_initial, CTLTYPE_INT|CTLFLAG_RW,
+    &tcp_rexmit_initial, 0, sysctl_msec_to_ticks, "I",
+    "Initial Retransmission Timeout");
+
 int	tcp_rexmit_min;
 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
@@ -668,7 +673,7 @@
 	TCPSTAT_INC(tcps_rexmttimeo);
 	if ((tp->t_state == TCPS_SYN_SENT) ||
 	    (tp->t_state == TCPS_SYN_RECEIVED))
-		rexmt = TCPTV_RTOBASE * tcp_backoff[tp->t_rxtshift];
+		rexmt = tcp_rexmit_initial * tcp_backoff[tp->t_rxtshift];
 	else
 		rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 	TCPT_RANGESET(tp->t_rxtcur, rexmt,