Subject: Re: Enable syn cookies by default

From: Eric Dumazet <[email-masked]>
Date: Wed, 21 Oct 2009 09:25:06 +0200

Olaf van der Spek a écrit :
> On Thu, Oct 15, 2009 at 10:59 AM, Olaf van der Spek
> <[email-masked]> wrote:
>> On Sat, Oct 10, 2009 at 3:01 PM, Olaf van der Spek <[email-masked]> wrote:
>>> Hi,
>>>
>>> I'm forwarding Debian feature request #520668.
>>>
>>> Could syn cookies be enabled by default?
>>>
>>> AFAIK syn cookies only get send when the half-open TCP connection
>>> queue is full. So stuff like window scaling should work fine in normal
>>> situations.
>>>
>>> Speaking of which:
>>> When the half-open TCP connection queue is full and syn cookies are
>>> enabled, you get a message like "kernel: possible SYN flooding on port
>>> 2710. Sending cookies."
>>> However when syn cookies are disabled, you don't get any message (in
>>> kern.log), although connections to your server are timing out.
>>> Could such a message be added?
>>> Maybe with a suggestion to increase the size of that queue or to
>>> enable syn cookies.
>>>
>>> Greetings,
>>>
>>> Olaf
>>>
>>> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=520668
>>> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=520667
>>> https://bugs.launchpad.net/ubuntu/+bug/57091
>>>
>> Somebody?
> 
> Anybody?

This is a user selectable setting. What's wrong with /etc/sysctl.conf ?