full-disclosure - DDos counter measures

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Message-ID: <5.2.1.1.2.20030814195711.01195280@belegost.cimternet.com>
From: llevier at argosnet.com (Laurent LEVIER)
Subject: DDos counter measures

All,

We found a simple solution to protect our IntraNet against the DDoS.

Since the msblast.exe will SYN flood windowsupdate.com (or 
windowsupdate.microsoft.com) with 50 packets per second (according to our 
tests).

Since our IntraNet solves all its DNS queries through internal caches 
(mandatory bottleneck), we created windowsupdate.com & 
windowsupdate.microsoft.com zones in this bottleneck DNS. These are 
resolving to 127.0.0.1 with DNS wildcards.

After the Microsoft DNS TTL has expired (15 minutes is the worst TTL), we 
got confirm all known windowsupdate domains hosts (www.windowsupdate.com, 
windowsupdate.microsoft.com, v3.windowsupdate.microsoft.com & 
v4.windowsupdate.microsoft.com) were resolved to localhost.

We expect now the worm to flood the box it is hosted on and so preserving 
our IntraNet.

Hope this can help others.

Brgrds

Laurent LEVIER
Equant Information Technology & Systems - Equant Security Organization - 
Internal Network (WAN IntraNet) - Systems & Networks Security Expert
Tel. CVN : 7223-1912, ext. (+33) 4 92 38 19 12