Re: Reflection DDoS last week (was: syn flood attacks from NL-based netblocks)

[Amir Herzberg <amir.lists () gmail com>]

Töma, thanks for this interesting update. The best defense against this
type of DDoS attacks seems idd to be relaying to
sufficiently-large-bandwidth cloud/CDN, and filtering TCP traffic (received
not from the relay). Such relaying should be done well - smart attacks may
still be possible for `naive' relaying.
-- 
Amir



On Wed, Aug 21, 2019 at 3:46 PM Töma Gavrichenkov <ximaera () gmail com> wrote:

> Peace,
>
> Here's to confirm that the pattern reported before in NANOG was indeed a
> reflection DDoS attack. On Sunday, it also hit our customer, here's the
> report:
>
>
> https://www.prnewswire.com/news-releases/root-cause-analysis-and-incident-report-on-the-august-ddos-attack-300905405.html
>
> tl;dr: basically that was a rather massive reflected SYN/ACK carpet
> bombing against several datacenter prefixes (no particular target was
> identified).
>
> --
> Töma
>
> On Sat, Aug 17, 2019, 1:06 AM Jim Shankland <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