D30740.id.diff
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	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 April 24, 2021
	+.Dd June 27, 2021
	.Dt TCP 4
	.Os
	.Sh NAME
	@@ -382,7 +382,9 @@
	connections for which support of
	.Tn TCP
	timestamps has been negotiated.
	-(default is 0, i.e., the missing of timestamps is not tolerated).
	+As of June 2021, several TCP stacks are known to violate RFC 7323, including
	+modern widely deployed ones.
	+Therefore the default is 1, i.e., the missing of timestamps is tolerated.
	.It Dv TCPCTL_MSSDFLT
	.Pq Va mssdflt
	The default value used for the maximum segment size
	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
	@@ -268,7 +268,14 @@
	&VNET_NAME(tcp_do_rfc1323), 0,
	"Enable rfc1323 (high performance TCP) extensions");

	-VNET_DEFINE(int, tcp_tolerate_missing_ts) = 0;
	+/*
	+ * As of June 2021, several TCP stacks violate RFC 7323 from September 2014.
	+ * Some stacks negotiate TS, but never send them after connection setup. Some
	+ * stacks negotiate TS, but don't send them when sending keep-alive segments.
	+ * These include modern widely deployed TCP stacks.
	+ * Therefore tolerating violations for now...
	+ */
	+VNET_DEFINE(int, tcp_tolerate_missing_ts) = 1;
	SYSCTL_INT(_net_inet_tcp, OID_AUTO, tolerate_missing_ts, CTLFLAG_VNET \| CTLFLAG_RW,
	&VNET_NAME(tcp_tolerate_missing_ts), 0,
	"Tolerate missing TCP timestamps");