Re: syn DDoS attack solution

["Tony.Ho" <support@idccenter.cn>]

I have a thought about this.
I can use ipset and iptables on a bridge firewall.

ipt_recent module compares the SYN package and ACK package's TTL. If not 
match then drop.
ipt_hashlimit module stores the concurrent connections. When the 
connections exceed the threshold iptables would store the IP in ipset.
ipset's iptree modules can store the IP in a fixed time. When a IP which 
is in the iptree's list comes the firewall iptables would TARPIT its tcp 
connection.
Is this setting effective?


Ric Messier wrote:
> Bgs writes:
>   
> >   We recently got under a low traffic botnet DDoS attack. All attacker
> > nodes opened a single tcp session (just SYN part) and then did nothing.
> > This rules out rate limiting solutions and syncookie doesn't help
> > either. (Thousands of attacking nodes).
> >
> >     
> This is simply a SYN flood attack. It may or may not be a botnet (though
> saying botnet makes it sound sexier :-) ). A decent SYN flood attack tool
> would randomize the source address anyway. 
>
> You should try reading the following as a starting point:
>
> http://www.securityfocus.com/infocus/1729
>
> Your second suggestion has been implemented in the TCP/IP stack forever. The
> article above gives guidance on how to tune it in a Linux implementation.
>
> Ric
>
>
>
>