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RE: Preventing DDOS Syn floods on HTTP servers
From: "Kathmann, Nicholas" <Nicholas.Kathmann () KaiserAl com>
Date: Thu, 11 Mar 2004 09:01:51 -0600

On windows:
   HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\SynAttachProtect
(REG_DWORD) - set to 2
 
HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\TcpMaxHalfOpenRetire
d(REG_DWORD) - Set to 80

This will provide some protection, but won't stop any big attack.  You
should try to block that type of traffic at your perimeter defenses (most
likely the firewall).

Nick

-----Original Message-----
From: Aditya, ALD [Aditya Lalit Deshmukh]
[mailto:aditya.deshmukh () online gateway technolabs net] 
Sent: Tuesday, March 09, 2004 11:18 PM
To: nabi1 () securology org; security-basics () securityfocus com
Subject: RE: Preveting DDOS Syn floods on HTTP servers

I was wondering if it was possible for a HTTP servers to prevent 
DDOS syn floods, attacks from different IP's, like a attack from 
a IRC network or something like that.

if you are using linux look into tcp_syncookies, a word of caution : it
requires a lot of physical memory and this allocated memory is non
swappable. increasing the value by a small bit would cause quite a bit of
increase in memory requirments

but your server would be able to handle syn floods more efficiently.


HTTP server cannot be hardened because syn scans are to be blocked by the os
: so harden your OS

-aditya


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