Krebs on Security booted off Akamai network after DDoS attack proves pricey
hugo at slabnet.com
Fri Sep 23 21:39:54 UTC 2016
On Fri 2016-Sep-23 17:29:59 -0400, Jared Mauch <jared at puck.nether.net> wrote:
>> On Sep 23, 2016, at 5:24 PM, Hugo Slabbert <hugo at slabnet.com> wrote:
>> Please tell me why I can't spoof source IPs on a stateless protocol like GRE. If he specifically meant you can't spoof a source, hit a reflector, and gain amplification, sure, but I see zero reason why GRE can't have spoofed source IPs. It bothered me sufficiently that I wrote up some spit-balling ideas about reflecting GRE using double encapsulation. Very rough and untested, but apparently I got a bee in my bonnet...
>my guess is the GRE traffic was harder to filter because many providers use GRE to deliver ‘clean’ traffic back to origin sites.
But those tunnels generally wouldn't terminate on addresses within the
protected block. If I'm protecting 126.96.36.199/24 for you, things would get
confused if my GRE tunnel dest is somewhere in 188.8.131.52/24 because I
would have a route for 184.108.40.206/24 across the GRE tunnel (either static
or more conventionally learned via BGP). I'd bank it on either a provider
touchdown or another unprotected block, otherwise I'd have a recursive
routing issue where the tunnel destination would get routed through the GRE
tunnel. I've been there with bouncy-bouncy tunnels on service turn-up when
that was flubbed.
Alternatively, I could pin /32s for the tunnel destinations and still learn
the shorter protected block, but even so I should then know which source
(my) and dest (customer's) IPs to exclude explicitly from the GRE
If the attackers were hitting the GRE tunnel destination and spoofing the
tunnel source that would make things harder, but that's starting to get
into rather intimate knowledge of the scrubber's and customer's setup. I
could still probably filter on e.g. TTLs or drop GRE further up to the
northern edge on input rather than output, but agreed that is starting to
Hugo Slabbert | email, xmpp/jabber: hugo at slabnet.com
pgp key: B178313E | also on Signal
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