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From "Ben Macintosh" <>
Subject [users@httpd] How to prevent from simple DoS?
Date Sun, 18 Nov 2007 15:28:36 GMT
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

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.

The only solutions I can see is lowering the timeout and increasing
MaxClients. Although a higher MaxClients probably won't help much,
because it's easy to start hundreds of sessions.
Regarding timeout - can I lower this drastically to about 5 secs
without creating new problems?

I'm using Apache 2.0.54 from Debian Sarge.
Here's a screenshot of the status page:

Any help appreciated

Thanks, Ben

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