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One of my servers is being flooded with udp packets on random ports.

12:11:54.190442 IP 182.48.38.227.60173 > localhost.51523: UDP, length 1
12:11:54.190447 IP 182.48.38.227.60173 > localhost.23769: UDP, length 1
12:11:54.190560 IP 182.48.38.227.60173 > localhost.4655: UDP, length 1
12:11:54.190564 IP 182.48.38.227.60173 > localhost.13002: UDP, length 1
12:11:54.190685 IP 182.48.38.227.60173 > localhost.52670: UDP, length 1
12:11:54.190690 IP 182.48.38.227.60173 > localhost.21266: UDP, length 1
12:11:54.190696 IP 182.48.38.227.60173 > localhost.7940: UDP, length 1
12:11:54.190810 IP 182.48.38.227.60173 > localhost.35950: UDP, length 1
12:11:54.190818 IP 182.48.38.227.60173 > localhost.62370: UDP, length 1
12:11:54.190828 IP 182.48.38.227.60173 > localhost.28225: UDP, length 1
12:11:54.190935 IP 182.48.38.227.60173 > localhost.56093: UDP, length 1
12:11:54.190939 IP 182.48.38.227.60173 > localhost.54250: UDP, length 1
12:11:54.190941 IP 182.48.38.227.60173 > localhost.15275: UDP, length 1
12:11:54.190948 IP 182.48.38.227.60173 > localhost.28750: UDP, length 1

I've got a lots of these. I know that if system gets an udp packet, it will check if any application want to handle it, if not, it will send a packet back. To prevent this I turned blackholing for udp on.

net.inet.udp.blackhole=1

I must add that I block every attacker with my pf (packet filter) and it seems to help, but he seems to have access to some botnet and changes source IP addresses like I change my socks OR he is just spoofing source ip of packets.

Anyway the attacker is still able to flood my server and I don't know how to defend from it.

I'd appreciate any help.

PS. I can't afford a hardware firewall ;)

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1 Answer 1

up vote 2 down vote accepted

The crucial data is this here:

length 1

meaning that someone probably is trying to keep its upstream load low to provoke larger answer packets from your host. The IP source address (182.48.38.227) is probably forged and thus itself an attack victim.

If you are experiencing network congestion due to the UDP load, your only chance of mitigating the impact is to ask your upstream provider to set up a filter rule to stop these UDP packets from being forwarded to your network.

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