Re: How to prevent from simple DoS?

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On Nov 18, 2007 10:28 AM, Ben Macintosh <bmac.list@xxxxxxxxx> wrote:
> Hi
> I'm currently facing a problem which I can't find any help for.
> Every once in a while, my webserver doesn't respond to requests
> anymore, i.e. the browser simply keeps on loading but doesn't get any
> data.
>
> Using the status mod I found that in such a situation every possible
> "slot" is being used by requests staying in "..reading.." status.
> After restarting apache all the pending requests get processed but
> after a few seconds all the slots are being blocked by the
> "..reading.." status again.
>
> After some tests I could reproduce the situation with simply
> initiating multiple telnet session to the webserver without sending
> any data. Every such request blocks a slot for the default timeout of
> 300 seconds.
>
> Is this common behaviour? If so, how to prevent it?
> As I understand the issue it's a very simple DoS as it neither does
> require a lot of cpu nor bandwidth on the client side.

See:
http://httpd.apache.org/docs/trunk/misc/security_tips.html#dos

The standard solution is a simple firewall rule to control number of
connections per ip at some reasonable level.

Joshua.

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