netdev - [PATCH] tcp: more documentation for tcp_tw_reuse and tcp_tw

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Date:	Sun,  4 May 2014 11:41:39 +0200
From:	Vincent Bernat <vincent@...nat.im>
To:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, linux-doc@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Cc:	Vincent Bernat <vincent@...nat.im>
Subject: [PATCH] tcp: more documentation for tcp_tw_reuse and tcp_tw_recycle

The documentation is not very helpful about what those settings
affect. We find numerous tuning guides advising to set both these
settings to 1 to reduce the number of entries in the TIME-WAIT
state. However, enabling tcp_tw_recycle will cause massive problems when
working with NAT.

The documentation is completed a bit to explain quickly what kind of
connections both those settings will affect and to encourage the use of
tcp_tw_reuse instead of tcp_tw_recycle for outgoing connections.
---
 Documentation/networking/ip-sysctl.txt | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index ab42c95f9985..d771aa064af8 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -532,14 +532,18 @@ tcp_tso_win_divisor - INTEGER
 	Default: 3
 
 tcp_tw_recycle - BOOLEAN
-	Enable fast recycling TIME-WAIT sockets. Default value is 0.
-	It should not be changed without advice/request of technical
+	Enable fast recycling TIME-WAIT sockets. Default value is
+	0. Enabling this option will cause problems when incoming
+	connections originate from NAT devices. For outgoing
+	connections, prefer the use of tcp_tw_reuse which is safer. It
+	should not be changed without advice/request of technical
 	experts.
 
 tcp_tw_reuse - BOOLEAN
-	Allow to reuse TIME-WAIT sockets for new connections when it is
-	safe from protocol viewpoint. Default value is 0.
-	It should not be changed without advice/request of technical
+	Allow to reuse TIME-WAIT sockets for new outgoing connections
+	when it is safe from protocol viewpoint. Default value is
+	0. This parameter has no effect on incoming connections.  It
+	should not be changed without advice/request of technical
 	experts.
 
 tcp_window_scaling - BOOLEAN
-- 
2.0.0.rc0

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