Subject: Re: Enable syn cookies by default

From: Jarek Poplawski <[email-masked]>
Date: Fri, 16 Oct 2009 08:55:41 +0000

On 15-10-2009 10:59, Olaf van der Spek 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?

Hi,

Alas, I can only give you a hint: while waiting for a better response,
you could try to 'google' for some archives of this list; AFAICR a few
(?) months ago David Miller explained this first question at least.
(In short: they aren't up-to-date enough.)

Regards,
Jarek P.

>>
>> 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?