Reduce effects of DDoS attack ...

Marc G. Fournier scrappy at
Thu Oct 7 08:19:29 PDT 2004

I've got 5 servers sitting on a 10/100 unmanaged switch right now ... last 
night, a DDoS attack against a network "beside us" cause 70+% packet loss 
on our network, and I'm trying to figure out if there is anything I can do 
from my side to "compensate" for this ...

I run ipaudit on all our servers, and a normal 30 minute period looks 

neptune# gzcat 2004-10-06-22:00.txt.gz | grep 200.046.204 | wc -l
neptune# gzcat 2004-10-06-22:00.txt.gz | grep -v 200.046.204 | wc -l
neptune# gzcat 2004-10-06-22:00.txt.gz | wc -l

where 200.046.204 is our C-class ...

Now, when the DDoS attack is running, those stats change to:

neptune# gzcat 2004-10-06-17:30.txt.gz | grep 200.046.204 | wc -l
neptune# gzcat 2004-10-06-17:30.txt.gz | grep -v 200.046.204 | wc -l
neptune# gzcat 2004-10-06-17:30.txt.gz | wc -l

We're getting *alot* of traffic on our network that just is not ours ...

Now, I can login to the servers, and load is negligible ... but packet 
loss is anywhere from 50->90%, so pretty much unusable ...

Now, the shared 'switch' between our networks is a Cisco Catalyst 2900xl 
... is there something that should be set on that so that I don't see that 
network traffic?  Basically, the only network traffic that I should/want 
to see is that for my network .. in this case, 200.46.204?

Baring that ... is there anything that I can do on the FreeBSD side of 
things to reduce the impact of the "extra packets"?  Some way of 
"absorbing them"?  For instance, if the packet is coming in, and it isn't 
for that server, then I imagine it has to 'bounce' it back out again, 
compounding the problem, no?

Also ... since the FreeBSD servers do seem to be handling the load, is it 
possible that the unmanaged switch that i have in place between the 
FreeBSD box and the Cisco switch is 'buckling under the load'?  Not able 
to handle the packets fast enough, and therefore just drop'ng them?

The unmanage switch is a 10/100 Linksys Switch ...

Thanks for any responses ...

Marc G. Fournier           Hub.Org Networking Services (
Email: scrappy at           Yahoo!: yscrappy              ICQ: 7615664

More information about the freebsd-questions mailing list