git: 870af3f4dc57 - main - tcp: tolerate missing timestamps
Michael Tuexen
tuexen at FreeBSD.org
Sun Jun 27 14:05:06 UTC 2021
The branch main has been updated by tuexen:
URL: https://cgit.FreeBSD.org/src/commit/?id=870af3f4dc57a6bbfc03f6a49ca0d5b7ff1b975a
commit 870af3f4dc57a6bbfc03f6a49ca0d5b7ff1b975a
Author: Michael Tuexen <tuexen at FreeBSD.org>
AuthorDate: 2021-06-11 18:14:34 +0000
Commit: Michael Tuexen <tuexen at FreeBSD.org>
CommitDate: 2021-06-27 14:03:57 +0000
tcp: tolerate missing timestamps
Some TCP stacks negotiate TS support, but do not send TS at all
or not for keep-alive segments. Since this includes modern widely
deployed stacks, tolerate the violation of RFC 7323 per default.
Reviewed by: rgrimes, rrs, rscheff
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D30740
Sponsored by: Netflix, Inc.
---
share/man/man4/tcp.4 | 6 ++++--
sys/netinet/tcp_subr.c | 9 ++++++++-
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index 93d1e075e92d..1ff1ee28420f 100644
--- 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 @@ segments belonging to
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
index a1531ea8d2f3..fbd84e763c0f 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -268,7 +268,14 @@ SYSCTL_INT(_net_inet_tcp, TCPCTL_DO_RFC1323, rfc1323, CTLFLAG_VNET | CTLFLAG_RW,
&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");
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