Re: New Denial of Service Attack on Panix

[Rashid Karimov <rashid () rk ios com>]

                How exactly proxy is supposed to behave 
                when it "hangs onto" say 10.000 + unfinished
                TCP connections ? Will it deny new ones (because
                resources are always limited) ?
                Looks like it's the only thing it will be able
                to do and as soon as first packet is denied,
                hacker's won.

                As hard as it is to be implemented the only way
                to fight this is have every single ISP to filter
                outgoing packets.
                Assuming big players have enough desire they can do it
                quickly by making an offer smaller ISPs can't refuse, 
                the same kind Sprint made when it started filtering
                small CIDRs.

                It's certainly harder to catch those who don't comply
                though ...

                Interestingly enough, the source IP's could be valid,
                then it becomes even harder to see if the TCP connection
                request is valid or bogus. And once again, source filtering
                by ea and every AS looks like the only solution.



> On Mon, 16 Sep 1996, Craig A. Huegen wrote:
>
> > The SYN flood coming towards my host X looks like this, at approximately
> > 2,000 PPS:
> >
> > 182.58.239.2.1526     -> 172.30.15.5.80  TCP SYN
> > 19.23.212.4.10294     -> 172.30.15.5.80  TCP SYN       
> > 93.29.233.68.4355     -> 172.30.15.5.80  TCP SYN
> > [... on and on ...]
> >
> > Tell me how to filter this.
>
> The only thing that comes close to the concept of "filtering" is to build
> a SYN proxy that replies with SYN-ACK and hangs onto SYN packets until the
> ACK is received from the net before actually letting the packets through
> to your server. This may require sequence number munging on every packet
> but that's generally the kind of thing proxies do. 
- - - - - - - - - - - - - - - - -