[PATCH man] tcp.7: improve paragraphs on tcp_ecn and add tcp_ecn_fallback bullet

[PATCH man] tcp.7: improve paragraphs on tcp_ecn and add tcp_ecn_fallback bullet

[Daniel Borkmann]

Improve description around tcp_ecn, fix the RFC number and it's not a
boolean anymore since long time, and add a description for tcp_ecn_fallback.

See also kernel doc under Documentation/networking/ip-sysctl.txt on
tcp_ecn and tcp_ecn_fallback.

Signed-off-by: Daniel Borkmann <daniel-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org>
---
 man7/tcp.7 | 35 ++++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/man7/tcp.7 b/man7/tcp.7
index 2f290a2..0409a66 100644
--- a/man7/tcp.7
+++ b/man7/tcp.7
@@ -396,12 +396,37 @@ option.
 .\" Since 2.4.0-test7
 Enable RFC\ 2883 TCP Duplicate SACK support.
 .TP
-.IR tcp_ecn " (Boolean; default: disabled; since Linux 2.4)"
+.IR tcp_ecn " (Integer; default: 2; since Linux 2.4)"
 .\" Since 2.4.0-test7
-Enable RFC\ 2884 Explicit Congestion Notification.
-When enabled, connectivity to some
-destinations could be affected due to older, misbehaving
-routers along the path causing connections to be dropped.
+Enable RFC\ 3168 Explicit Congestion Notification.
+
+This file can have one of the following values:
+.RS
+.IP 0
+Disable ECN.
+Neither initiate nor accept ECN.
+.IP 1
+Enable ECN when requested by incoming connections and also
+request ECN on outgoing connection attempts.
+.IP 2
+Enable ECN when requested by incoming connections,
+but do not request ECN on outgoing connections.
+.RE
+.IP
+When enabled, connectivity to some destinations could be affected
+due to older, misbehaving middle boxes along the path, causing
+connections to be dropped.
+However, to facilitate and encourage deployment with option 1, and
+to work around such buggy equipment,
+.B tcp_ecn_fallback
+option has been introduced.
+.TP
+.IR tcp_ecn_fallback " (Boolean; default: enabled; since Linux 4.1)"
+.\" commit 492135557dc090a1abb2cfbe1a412757e3ed68ab
+Enable RFC\ 3168, Section 6.1.1.1. fallback.
+When enabled, outgoing ECN-setup SYNs that time out within the
+normal SYN retransmission timeout will be resent with CWR and
+ECE cleared.
 .TP
 .IR tcp_fack " (Boolean; default: enabled; since Linux 2.2)"
 .\" Since 2.1.92
-- 
1.9.3

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Re: [PATCH man] tcp.7: improve paragraphs on tcp_ecn and add tcp_ecn_fallback bullet

[Michael Kerrisk (man-pages)]

Hi Daniel,

On 08/26/2015 02:02 PM, Daniel Borkmann wrote:
> Improve description around tcp_ecn, fix the RFC number and it's not a
> boolean anymore since long time, and add a description for tcp_ecn_fallback.
> 
> See also kernel doc under Documentation/networking/ip-sysctl.txt on
> tcp_ecn and tcp_ecn_fallback.

Thanks for this.

> Signed-off-by: Daniel Borkmann <daniel-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org>
> ---
>  man7/tcp.7 | 35 ++++++++++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 5 deletions(-)
> 
> diff --git a/man7/tcp.7 b/man7/tcp.7
> index 2f290a2..0409a66 100644
> --- a/man7/tcp.7
> +++ b/man7/tcp.7
> @@ -396,12 +396,37 @@ option.
>  .\" Since 2.4.0-test7
>  Enable RFC\ 2883 TCP Duplicate SACK support.
>  .TP
> -.IR tcp_ecn " (Boolean; default: disabled; since Linux 2.4)"
> +.IR tcp_ecn " (Integer; default: 2; since Linux 2.4)"
>  .\" Since 2.4.0-test7
> -Enable RFC\ 2884 Explicit Congestion Notification.
> -When enabled, connectivity to some
> -destinations could be affected due to older, misbehaving
> -routers along the path causing connections to be dropped.
> +Enable RFC\ 3168 Explicit Congestion Notification.
> +
> +This file can have one of the following values:
> +.RS
> +.IP 0
> +Disable ECN.
> +Neither initiate nor accept ECN.
> +.IP 1
> +Enable ECN when requested by incoming connections and also
> +request ECN on outgoing connection attempts.
> +.IP 2
> +Enable ECN when requested by incoming connections,
> +but do not request ECN on outgoing connections.

I also added a note here that option 2 first appeared in Linux 2.6.31.

> +.RE

> +.IP
> +When enabled, connectivity to some destinations could be affected
> +due to older, misbehaving middle boxes along the path, causing
> +connections to be dropped.
> +However, to facilitate and encourage deployment with option 1, and
> +to work around such buggy equipment,
> +.B tcp_ecn_fallback
> +option has been introduced.
> +.TP
> +.IR tcp_ecn_fallback " (Boolean; default: enabled; since Linux 4.1)"
> +.\" commit 492135557dc090a1abb2cfbe1a412757e3ed68ab

(Thanks for including the commit ID.)

> +Enable RFC\ 3168, Section 6.1.1.1. fallback.
> +When enabled, outgoing ECN-setup SYNs that time out within the
> +normal SYN retransmission timeout will be resent with CWR and
> +ECE cleared.
>  .TP
>  .IR tcp_fack " (Boolean; default: enabled; since Linux 2.2)"
>  .\" Since 2.1.92

Thanks. Applied. Sorry for the delay.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: [PATCH man] tcp.7: improve paragraphs on tcp_ecn and add tcp_ecn_fallback bullet

[Daniel Borkmann]

On 09/11/2015 11:16 AM, Michael Kerrisk (man-pages) wrote:
...
>> +.IP 2
>> +Enable ECN when requested by incoming connections,
>> +but do not request ECN on outgoing connections.
>
> I also added a note here that option 2 first appeared in Linux 2.6.31.

Great, thanks a lot!
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