syn flood attacks from NL-based netblocks

Curtis, Bruce bruce.curtis at
Fri Aug 16 22:18:28 UTC 2019

On Aug 16, 2019, at 5:04 PM, Jim Shankland <nanog at<mailto:nanog at>> wrote:


I'm seeing slow-motion (a few per second, per IP/port pair) syn flood attacks ostensibly originating from 3 NL-based IP blocks: ,, and ("ostensibly" because ... syn flood, and BCP 38 not yet fully adopted).

Why is this syn flood different from all other syn floods? Well ...

1. Rate seems too slow to do any actual damage (is anybody really bothered by a few bad SYN packets per second per service, at this point?); but

2. IPs/port combinations with actual open services are being targeted (I'm seeing ports 22, 443, and 53, just at a glance, to specific IPs with those services running), implying somebody checked for open services first;

3. I'm seeing this in at least 2 locations, to addresses in different, completely unrelated ASes, implying it may be pretty widespread.

Is anybody else seeing the same thing? Any thoughts on what's going on? Or should I just be ignoring this and getting on with the weekend?


We are seeing that here also.  Saw similar traffic ostensibly originating from NL at least as long ago as last Sunday August 17.

Bruce Curtis                         bruce.curtis at<mailto:bruce.curtis at>
Certified NetAnalyst II                701-231-8527
North Dakota State University

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