Basic Idea ::
The Attacker/Hacker will notify all the Computers on the Botnet to keep in touch with the Website/Server from time to time.This increases traffic on the Network that causes slowing down of the Website/Web server. If Sometimes the Traffic is Exceptionally High that can lead to the Complete Shutting Down of the Website or Server.
Tips to Prevent a DDOS Attack ::
In case you have computer System which are Connected directly to Web, then it is better to Configure your Router and Firewall Settings and Only allowing traffic to pass on few Chosen Ports like HTTP,SMTP via the Firewall.
2)Get More Bandwidth
It is one of the Easiest way but is Requires more Money.With Increasing your Bandwidth you will able to handle/tackle a lot of low scale DDOS Attacks.Well DDOS is just like a Capacity game ,How much capacity your Bandwidth has and How much Traffic it can Handle.
3)Get to a DDOS Mitigation Services
I personally recommend it is the Best Option because Wasting Money on buying more Bandwidth would not work at the High Level as Current DDOS attacks are getting Large which can exceed your Budget.Look for an ISP having the Largest DDOS Protection and Mitigation Network,Tools and Of course it would be having a Team of Talented DDOS technicians.
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