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tcp: tolerate missing timestamps

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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.
This commit is contained in:
Michael Tuexen 2021-06-11 20:14:34 +02:00
parent 19c288b3a6
commit 870af3f4dc
2 changed files with 12 additions and 3 deletions
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6
share/man/man4/tcp.4
View File

@ -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

9
sys/netinet/tcp_subr.c
View File

@ -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");