Re: syn flood attacks from NL-based netblocks

["Curtis, Bruce" <bruce.curtis () ndsu edu>]

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

Greetings,

I'm seeing slow-motion (a few per second, per IP/port pair) syn flood attacks ostensibly originating from 3 NL-based IP 
blocks: 88.208.0.0/18 , 5.11.80.0/21, and 78.140.128.0/18 ("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?

Jim

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 () ndsu edu<mailto:bruce.curtis () ndsu edu>
Certified NetAnalyst II                701-231-8527
North Dakota State University