From: "H.K. Jerry Chu" <hkjerry.chu@gmail.com>
To: Alex Bergmann <alex@linlab.net>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] tcp: Wrong timeout for SYN segments
Date: Wed, 22 Aug 2012 09:44:10 -0700 [thread overview]
Message-ID: <CAFbMe2NVbjGyEF9VRj9p_ejx3mGKTPT2urnguLtfRZEMShsO4g@mail.gmail.com> (raw)
In-Reply-To: <503419D3.1080700@linlab.net>
On Tue, Aug 21, 2012 at 4:29 PM, Alex Bergmann <alex@linlab.net> wrote:
> Hi David,
>
> I'm not 100% sure, but it looks like I found an RFC mismatch with the
> current default values of the TCP implementation.
>
> Alex
>
> From 8b854a525eb45f64ad29dfab16f9d9f681e84495 Mon Sep 17 00:00:00 2001
> From: Alexander Bergmann <alex@linlab.net>
> Date: Wed, 22 Aug 2012 00:29:08 +0200
> Subject: [PATCH 1/1] tcp: Wrong timeout for SYN segments
>
> Commit 9ad7c049 changed the initRTO from 3secs to 1sec in accordance to
> RFC6298 (former RFC2988bis). This introduced a gap with RFC1122 that
> defines a minimum retransmission window for SYN segments of at least
> 180secs.
>
> Prior to 9ad7c049 the timeout was defined with 189secs. Now we have only
> a timeout of 63secs.
>
> ((2 << 5) - 1) * 3 secs = 189 secs
> ((2 << 5) - 1) * 1 secs = 63 secs
>
> To fulfill the MUST constraint in RFC1122 section 4.2.3.5 about R2 for
> SYN segments, the values of TCP_SYN_RETRIES and TCP_SYNACK_RETRIES must
> be changed to 7 reties.
>
> ((2 << 7) - 1) * 1 secs = 255 secs
>
> This would result in an ETIMEDOUT of 4 minutes 15 seconds.
This issue occurred to me right after I submitted the patch for RFC6298.
I did not commit any more change because RFC compliance aside, 180secs
just seem like eternity in the Internet age.
(See my past post on this at
http://marc.info/?l=linux-netdev&m=130759078118866&w=2)
Jerry
>
> Signed-off-by: Alexander Bergmann <alex@linlab.net>
> ---
> include/net/tcp.h | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 1f000ff..7eaae19 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -98,10 +98,10 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
> * 15 is ~13-30min depending on RTO.
> */
>
> -#define TCP_SYN_RETRIES 5 /* number of times to retry active opening a
> +#define TCP_SYN_RETRIES 7 /* number of times to retry active opening a
> * connection: ~180sec is RFC minimum */
>
> -#define TCP_SYNACK_RETRIES 5 /* number of times to retry passive opening a
> +#define TCP_SYNACK_RETRIES 7 /* number of times to retry passive opening a
> * connection: ~180sec is RFC minimum */
>
> #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
> --
> 1.7.8.6
>
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
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next prev parent reply other threads:[~2012-08-22 16:44 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-21 23:29 [PATCH 1/1] tcp: Wrong timeout for SYN segments Alex Bergmann
2012-08-22 8:06 ` Eric Dumazet
2012-08-22 8:48 ` Alex Bergmann
2012-08-22 8:58 ` Eric Dumazet
2012-08-22 9:29 ` Alex Bergmann
2012-08-22 9:59 ` Eric Dumazet
2012-08-22 10:03 ` Eric Dumazet
2012-08-22 17:29 ` H.K. Jerry Chu
2012-08-22 16:44 ` H.K. Jerry Chu [this message]
[not found] ` <CAFbMe2M7ekc94bQk7vTS1LhScPd49VZ-zKOCUXhqwxXtL-nkuA@mail.gmail.com>
2012-08-23 11:58 ` Alex Bergmann
2012-08-23 12:15 ` Eric Dumazet
2012-08-23 12:35 ` David Laight
2012-08-23 12:51 ` Eric Dumazet
2012-08-23 12:37 ` Alex Bergmann
2012-08-23 12:49 ` Eric Dumazet
2012-08-24 12:17 ` Alex Bergmann
2012-08-24 17:42 ` David Miller
2012-08-25 8:48 ` Alexander Bergmann
2012-08-25 9:01 ` Eric Dumazet
2012-08-28 8:44 ` Carsten Wolff
[not found] ` <1346414260.2591.8.camel@edumazet-glaptop>
2012-08-31 12:48 ` Alexander Bergmann
2012-08-31 13:25 ` Eric Dumazet
2012-08-31 19:42 ` David Miller
2012-08-31 19:47 ` David Miller
2012-08-29 4:34 ` H.K. Jerry Chu
2012-08-29 8:51 ` Eric Dumazet
2012-08-29 17:25 ` H.K. Jerry Chu
2012-08-30 13:12 ` Eric Dumazet
2012-08-30 16:45 ` David Miller
2012-08-30 18:04 ` H.K. Jerry Chu
2012-08-30 17:59 ` H.K. Jerry Chu
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