1 files changed, 10 insertions, 1 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index ec5de02f543f..7f98aa3962c6 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -168,7 +168,16 @@ tcp_dsack - BOOLEAN
         Allows TCP to send "duplicate" SACKs.
 
 tcp_ecn - BOOLEAN
-        Enable Explicit Congestion Notification in TCP.
+        Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
+        used when both ends of the TCP flow support it. It is useful to
+        avoid losses due to congestion (when the bottleneck router supports
+        ECN).
+        Possible values are:
+                0 disable ECN
+                1 ECN enabled
+                2 Only server-side ECN enabled. If the other end does
+                  not support ECN, behavior is like with ECN disabled.
+        Default: 2
 
 tcp_fack - BOOLEAN
         Enable FACK congestion avoidance and fast retransmission.