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-rw-r--r--Documentation/networking/ip-sysctl.txt11
-rw-r--r--net/ipv4/tcp_input.c2
-rw-r--r--net/ipv4/tcp_output.c2
3 files changed, 12 insertions, 3 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.
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c96a6bb25430..56dcf97a97fb 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -77,7 +77,7 @@ int sysctl_tcp_window_scaling __read_mostly = 1;
int sysctl_tcp_sack __read_mostly = 1;
int sysctl_tcp_fack __read_mostly = 1;
int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
-int sysctl_tcp_ecn __read_mostly;
+int sysctl_tcp_ecn __read_mostly = 2;
int sysctl_tcp_dsack __read_mostly = 1;
int sysctl_tcp_app_win __read_mostly = 31;
int sysctl_tcp_adv_win_scale __read_mostly = 2;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 59aec609cec6..79c39dc9b01c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -288,7 +288,7 @@ static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
struct tcp_sock *tp = tcp_sk(sk);
tp->ecn_flags = 0;
- if (sysctl_tcp_ecn) {
+ if (sysctl_tcp_ecn == 1) {
TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ECE | TCPCB_FLAG_CWR;
tp->ecn_flags = TCP_ECN_OK;
}