Date: Tue, 20 May 2008 15:10:05 GMT From: Andre Oppermann <andre@freebsd.org> To: freebsd-net@FreeBSD.org Subject: Re: amd64/123603: tcp_do_segment and Received duplicate SYN Message-ID: <200805201510.m4KFA5TK086435@freefall.freebsd.org>
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The following reply was made to PR kern/123603; it has been noted by GNATS.
From: Andre Oppermann <andre@freebsd.org>
To: yes298 yes298 <yes298@gmail.com>
Cc: John Baldwin <jhb@freebsd.org>, freebsd-gnats-submit@freebsd.org
Subject: Re: amd64/123603: tcp_do_segment and Received duplicate SYN
Date: Tue, 20 May 2008 16:40:08 +0200
Victor,
Please try two things:
1. Make sure that you don't have a problem with MTU sizes. Some ADSL
customers with PPPoE have slightly smaller MTU sizes than normal
ethernet. Make sure that ICMP unreach packets are not firewalled
or filtered on your side.
2. There was a bug in the TCP options in FreeBSD 7.0-RELEASE that was
giving problems with a smaller number of CPE devices for ADSL and
Cablemodem customers. The problem is fixed in 7-STABLE. Only upgrading
the kernel is sufficient.
I hope this helps. If not, please provide some tcpdumps so we can see
the packets that are exchanged.
--
Andre
yes298 yes298 wrote:
> Dear Sir,
>
> Thank you so much for your reply.
>
> My FreeBSD 7.0(x64) Lighttpd web server connects to a 100M broadband line,
> after testing many times, I found that, when first time to view my website,
> it needed to take almost 5~8 seconds to completely open the homepage which
> is only a static HTML file with content "coming soon", and there are some
> error log about TCP connection found on our web server, it seems that my
> FreeBSD 7.0 web server has problem to establish TCP connection. Before the
> web server idle time (30s), there are no any delay to re-view the homepage
> (Press F5), but after 30 seconds, it needed to take another 5~8 seconds to
> re-view, and the log messages will be repeated.
>
> May 15 15:18:21 mail kernel: TCP: [203.186.95.8]:12728 to [58.177.222.113]:80
> tcpflags 0x2<SYN>; syncache_add: Received duplicate SYN, resetting timer and
> retransmitting SYN|ACK
> May 15 15:19:03 mail kernel: TCP: [221.127.88.188]:5128 to [58.177.222.113]:80
> tcpflags 0x2<SYN>; syncache_add: Received duplicate SYN, resetting timer and
> retransmitting SYN|ACK
>
> I know how to disable these log messages, but I would like to know that the
> delay is because
> of receiving duplicate SYN? is it normal message? Please help me to solve
> the problem, thanks !!!!
> Thank you so much!
>
> Best regards,
> Victor
>
> 2008/5/19 John Baldwin <jhb@freebsd.org>:
>
>> On Monday 12 May 2008 03:45:16 am John wrote:
>>>> Number: 123603
>>>> Category: amd64
>>>> Synopsis: tcp_do_segment and Received duplicate SYN
>>>> Confidential: no
>>>> Severity: critical
>>>> Priority: high
>>>> Responsible: freebsd-amd64
>>>> State: open
>>>> Quarter:
>>>> Keywords:
>>>> Date-Required:
>>>> Class: sw-bug
>>>> Submitter-Id: current-users
>>>> Arrival-Date: Mon May 12 07:50:01 UTC 2008
>>>> Closed-Date:
>>>> Last-Modified:
>>>> Originator: John
>>>> Release: FB7.0 (x64)
>>>> Organization:
>>> NULL
>>>
>>>> Environment:
>>> FreeBSD mail.mydomain.com 7.0-RELEASE FreeBSD 7.0-RELEASE #0: Thu Mar 6
>>> 12:04:57 HKT 2008 root@mydomain.com:
>> /usr/src/sys/amd64/compile/FB7NEW
>>> amd64
>>>
>>>> Description:
>>> A FreeBSD 7.0 (x64) Lighttpd Web Server with most-updated ports and
>> patchs.
>>> when a client connect and view a static HTML file, At the first time
>>> (before web server idle time), it needs to wait a long time to establish
>> a
>>> connection, OR when this server try to download file from Internet, there
>>> are lots of logs messages just like below:
>>>
>>> May 12 11:57:54 mail kernel: TCP: [55.66.77.88]:41792 to [11.22.33.44
>> ]:80
>>> tcpflags 0x2<SYN>; syncache_add: Received duplicate SYN, resetting timer
>>> and retransmitting SYN|ACK
>>> May 12 15:17:53 mail kernel: TCP: [193.166.3.2]:45979 to
>>> [11.22.33.44]:63372 tcpflags 0x10<ACK>; tcp_do_segment: FIN_WAIT_1:
>>> Received 1448 bytes of data after socket was closed, sending RST and
>>> removing tcpcb May 12 15:17:53 mail kernel: TCP: [193.166.3.2]:21 to
>>> [11.22.33.44]:55007 tcpflags 0x18<PUSH,ACK>; tcp_do_segment: FIN_WAIT_2:
>>> Received 13 bytes of data after socket was closed, sending RST and
>> removing
>>> tcpcb
>>>
>>>> How-To-Repeat:
>>> any type of connection will generate above log messages.
>> You can either comment out all the log(LOG_DEBUG, ...) calls
>> in /sys/netinet/tcp*.c or change your /etc/syslog.conf to not send
>> kern.debug
>> messages to the console.
>>
>> I think these messages should probably be conditional on a kernel option
>> FWIW.
>>
>> --
>> John Baldwin
>>
>
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