netdev - Re: why do we need printk on sending syn flood cookie?

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Date:	Mon, 2 Aug 2010 11:10:01 -0700
From:	Mitchell Erblich <erblichs@...thlink.net>
To:	Franchoze Eric <franchoze@...dex.ru>
Cc:	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: why do we need printk on sending syn flood cookie?

On Aug 2, 2010, at 9:11 AM, Franchoze Eric wrote:

> 
> 
> 02.08.10, 12:17, "Florian Westphal" <fw@...len.de>:
> 
>> Franchoze Eric  wrote:
>>> Just sirious why do we need printk each 1 second (60*HZ) about possible syn-flood? It really floods dmesg. Is there something dengerous? I have suggestion to turn off printk about sending tcp cookie each 1 second.
>> 
>> It is handled exactly like other printks in the networking path,
>> e.g. receipt of tcp wscale == 15.
>> 
>> Why does this need special treatment?
>> 
> 
> For now I see "possible SYN flooding on port %d. Sending cookies.\n" message each second on my server. I know that there are a lot of SYNs and I know that kernel sends cookie. Why do I need so mach printk?
> So I suggested add new value to /proc/sys/net/ipv4/tcp_syncookies, which will enable cookie but this printk will be turned off.

Once print per sec is a very good GENERIC informative msg to an admin that 
this system either has some  very small config'd or default values
(normally set up as a percentage of memory or set sock option and/or .. )
and/or that for some reason that a large number of SYNs are being rec'vd
and/or that a number of connections are being un/intentionally being
retried and/or dropped

Remember each printk may only be a small fraction of the number of SYNs
rcv'd and this fraction COULD depend on the Mb/Gb of the intf(s) or more
likely some type of  avg of summation of the number of network paths
involved.

Mitchell Erblich

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