DDOS Attack
 

Hello,
My server is under ddos attack.(with vBulletin 3.8.0)
What i do?

Talk to your host, there is nothing much (effective) that you can do.

I can root access.

There really isn't a whole lot you can do. The host needs to stop this at the router, if possible, otherwise you kinda have to wait it out. There are some scripts out there to help ip ban some of these users/computers, but that only helps so much. When we were under ddos attack, I used a script and it basically just allowed the users to painfully surf the site versus not being able to get on at all. In my case, they left four days later as abruptly as they came.

you can pass protect your forum, but that will block search engines

I reccomend install mod_defalte it helps to ban some of the incoming IP. To stop a DDoS attacker you have to know how to be a DDoS Attacker. I reccomend paying the extra 50 dollars a month to get a hardware firewall.

Lets start out by asking who are you hosted with.

I say the host because as long as the traffic is battering your box, you are effectively powerless. The traffic needs to be stopped from reaching your box. And this is something only your host/the datacentre can do.

Block all search engines? with robots.txt ? etc:google , yahoo and ... . ?

That will pop up a login box everytime someone tries to access your site.
Example: https://vborg.vbsupport.ru/admincp