linux-kernel - [PATCH] Documentation/networking/ip-sysctl.txt tcp_tw_recycle & tcp_tw

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Date:	Mon,  4 Oct 2010 19:32:04 +0200
From:	Sami Kerola <kerolasa@....fi>
To:	linux-doc@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, davem@...emloft.net,
	Sami Kerola <kerolasa@....fi>
Subject: [PATCH] Documentation/networking/ip-sysctl.txt tcp_tw_recycle & tcp_tw_reuse

From: Sami Kerola <kerolasa@....fi>

Instead of saying 'consult your technical export' the
documentation needs to assist an export to decide whether to keep
these settings off or set them on.

Signed-off-by: Sami Kerola <kerolasa@....fi>
---
 Documentation/networking/ip-sysctl.txt |   20 +++++++++++++-------
 1 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index f350c69..01e2948 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -444,15 +444,21 @@ 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
-	experts.
+	Enable fast recycling TIME-WAIT sockets. See also caution
+	wrote to tcp_tw_reuse. Default value is 0.
 
 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
-	experts.
+	Allow to reuse TIME-WAIT sockets for new connections when it is safe
+	from protocol viewpoint. One should enable also tcp_timestamps when
+	this is enabled. Default value is 0.
+
+	Caution. Both tcp_tw_recycle and tcp_tw_reuse can cause problems. You
+	should not enable either without being sure about network topology in
+	between node(s) which are using, or used by, the node(s) where the
+	parameter is enabled. Connections that go via TCP state aware nodes,
+	such as firewalls, NAT devices or load balancers may start drop frames
+	because of the setting. The more there are connections the greater is
+	the likelyhood you will see this issue.
 
 tcp_window_scaling - BOOLEAN
 	Enable window scaling as defined in RFC1323.
-- 
1.7.3.1

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