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DOS attack

Posted on 2006-11-23
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What techniques are used to secure against DOS attacks, i.e. someone killing the signal over WI-FI?
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Question by:pma111
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rsivanandan earned 125 total points
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A stateful firewall which does proxy service would help you protect from the dos attacks.

In a denial of service attack, remote host(s) keep send the syn packet which basically is flooded a machine (usually a webserver kinda) and when its tcp/ip buffer runs over it breaks down.

So when you put in a firewall, what it does is it takes the hit on the firewall and saves the internal machines from doing it.

How it does?
1. An external host sends a syn packet.
2. Firewall responds with a syn+ack to the external host (at this point, the internal server doesn't even know that there is something going on like this).
3. If the external hosts sends an ack packet, then the firewall creates a new session by syn to ack to the internal server.
4. Then it connects them together so that the communication works.

So when somebody does the DOS attack by the syn, the firewall protects and it will let the connection go in only if the tcp/ip three way handshake is completed first with the external host.

Hope that explains.

Some products to look at www.juniper.com and www.cisco.com

Both have good firewalls and you can choose the product based on your requirements.

Cheers,
Rajesh
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