From: Videau Brice <brice.videau@imag.fr>
To: Eric Dumazet <dada1@cosmosbay.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Strange connect behavior
Date: Mon, 30 Oct 2006 12:24:07 +0100 [thread overview]
Message-ID: <4545E0D7.6010608@imag.fr> (raw)
In-Reply-To: <200610301132.57769.dada1@cosmosbay.com>
It all makes sense now!
Thank you very much.
Regards,
Brice
Eric Dumazet wrote:
> On Monday 30 October 2006 11:24, Videau Brice wrote:
>
>> Hello,
>>
>> While writing some client server application in c, we noticed a strange
>> behavior : if we try to connect endlessly to a given local port where
>> nobody is listening, and if the port is >= to 32768, after several
>> thousands tries ( Connection refused ) connect will return 0.
>> This behavior is not exhibited when port is < 32768.
>>
>>
>
> Hello Brice
>
> Yes, it's quite possible your attempts are hitting themselves.
>
> Hint :
>
> cat /proc/sys/net/ipv4/ip_local_port_range
>
> When you connect(), TCP stack automatically chose a source port and bind your
> outgoing socket. If the chosen port happens to be 35489 (your 'destination'
> port), then the connect succeeds (you're connected to yourself), as specified
> by TCP specs.
>
>
>
>> We confirmed this behavior in kernel 2.6.17-10, 2.6.18-1, 2.6.8, on x86
>> and 2.4.21-32 on ia64, on several hardware configurations.
>> Distribution is debian or ubuntu.
>>
>> Attached is a source file that demonstrate this behavior.
>> ./a.out port_number
>>
>> Sample execution :
>>
>> ./a.out 35489
>> Out port : 35489
>> connect try 1 failed : Connection refused
>> connect try 2 failed : Connection refused
>> connect try 3 failed : Connection refused
>> .....
>> connect try 6089 failed : Connection refused
>> connect try 6090 failed : Connection refused
>> Connection success : 6091 try
>> Connection closed
>> last error : Connection refused
>>
>>
>> Is this behavior to be expected?
>> Can it be disabled?
>>
>> Thanks in advance.
>>
>> Regards,
>>
>> Brice Videau
>>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
>
prev parent reply other threads:[~2006-10-30 11:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-30 10:24 Strange connect behavior Videau Brice
2006-10-30 10:32 ` Eric Dumazet
2006-10-30 11:24 ` Videau Brice [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4545E0D7.6010608@imag.fr \
--to=brice.videau@imag.fr \
--cc=dada1@cosmosbay.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox