Messages in this thread | | | Date | Wed, 22 Aug 2012 09:44:10 -0700 | Subject | Re: [PATCH 1/1] tcp: Wrong timeout for SYN segments | From | "H.K. Jerry Chu" <> |
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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 > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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