From 22efabd40c4ad415dbdf68a105a3fa654ac35f7f Mon Sep 17 00:00:00 2001
From: Andre Oppermann <andre@FreeBSD.org>
Date: Sun, 28 Oct 2012 17:16:09 +0000
Subject: [PATCH] Adjust the initial default CWND upon connection establishment
 to the new and increased values specified by RFC5681 Section 3.1.

The even larger initial CWND per RFC3390, if enabled, is not affected.

MFC after:	2 weeks
---
 sys/netinet/tcp_input.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index 1d56dfd9b4e..62819cfd6d1 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -351,8 +351,15 @@ cc_conn_init(struct tcpcb *tp)
 	if (V_tcp_do_rfc3390)
 		tp->snd_cwnd = min(4 * tp->t_maxseg,
 		    max(2 * tp->t_maxseg, 4380));
-	else
-		tp->snd_cwnd = tp->t_maxseg;
+	else {
+		/* Per RFC5681 Section 3.1 */
+		if (tp->t_maxseg > 2190)
+			tp->snd_cwnd = 2 * tp->t_maxseg;
+		else if (tp->t_maxseg > 1095)
+			tp->snd_cwnd = 3 * tp->t_maxseg;
+		else
+			tp->snd_cwnd = 4 * tp->t_maxseg;
+	}
 
 	if (CC_ALGO(tp)->conn_init != NULL)
 		CC_ALGO(tp)->conn_init(tp->ccv);