Re: Need help please

Gordan Bobic
2003-03-20T12:42:30Z

On Thursday 20 Mar 2003 12:49, Webadmin wrote:

> We''ve been getting some DDOS attack recently, due to this I was
just
> wondering if we use some network traffic control techniques in order to
> reduce the risk of having the DDOS attack?? is this possible after all??
> can we use the traffic control techniques in order to redu reduce the DDOS
> attack???

I don''t think you can reduce the "risk" of being under
attack.

What sort of an attack are you under? Ping/ICMP flood? Or just a lot of robots
killing your web server with seemingly valid requests?

If you are having your bandwidth between your router and your ISPs all used up
by the attack, then you may be out of luck, as congestion and dropping will
most likely occur before any valid traffic gets through to you.

OTOH, if it is just your server load that is being affected, then yes, you
could potentially do something about it, provided you have some bandwidth to
spare. You could block or reduce the priority of the offending traffic. You
could also analyze logs what hosts are consuming a large amount of resources,
or analyze the headers they are sending, and try to separate valid traffic by
that. Then, just drop all traffic to/from the offending hosts completely, or
reduce their traffic to a minimum priority. You can do this using
ipchains/iptables and setting fwmarks on packets to/from relevant machines,
and then filtering on fwmarks.

Ideally, you might be able to ask your ISP to filter out the offending traffic
before it hits your local router, so it doesn''t consume your bandwidth,
but
that depends on what they are able/willing to do with their network setup to
help you out...

I think you will have to be a little more specific about the type of attack
you are under for any more specific suggestions...

Regards.

Gordan