Linked by Thom Holwerda on Thu 28th Mar 2013 00:36 UTC, submitted by MOS6510
Internet & Networking "The New York Times this morning published a story about the Spamhaus DDoS attack and how CloudFlare helped mitigate it and keep the site online. The Times calls the attack the largest known DDoS attack ever on the Internet. We wrote about the attack last week. At the time, it was a large attack, sending 85Gbps of traffic. Since then, the attack got much worse. Here are some of the technical details of what we've seen."
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Laurence
Member since:
2007-03-26


I'm no expert either, but your solution sounds more complicated (and, hence, more CPU intensive on the routers) than what they were proposing. It sounded like they were just proposing plain old source-interface checking so, when the attacker sends a spoofed packet to a DNS server, one of the border routers along the way drops it for arriving on the wrong interface.

We're talking about the same check. What I was describing was the process behind "plain old source-interface checking".

Also, I believe it was the CloudFlare commenter who pointed out that this isn't the first attack of this kind. Before spoofed UDP flooding via DNS, there was spoofed SYN flooding.

Totally. But AFAIK we've never seen the same degree of amplification (eg every bit being multiplied up to as much as 10bits) before, not even with SYN flooding. Which is where attacking open resolvers come into play.

I might be wrong on this though so welcome any corrections ;)

Reply Parent Score: 2

Alfman Member since:
2011-01-28

Laurence,

"We're talking about the same check. What I was describing was the process behind 'plain old source-interface checking'."

It doesn't seem like source interface filtering is a great solution to me because on the internet there's technically no requirement that packets come in from the same interface they'll return out of. In multi-homed setups this can even be explicit. Load balancers might do the same thing. But even in other less exotic cases internet routers can switch paths dynamically as they rerun the shortest path algorithms, I don't know just how frequently this happens, but it's the reason UDP packets can arrive out of order.

So do you agree that source interface filtering could negatively affect legitimate users?

It's a DNS problem, so I feel that a DNS fix should be used instead of modifying our routers. It's much easier to update dns software than a router. My understanding is that many commercial routers achieve their performance in hardware and become underpowered if too many packets get tossed around into the software stack.

Edited 2013-03-28 14:43 UTC

Reply Parent Score: 3

Laurence Member since:
2007-03-26

t doesn't seem like source interface filtering is a great solution to me because on the internet there's technically no requirement that packets come in from the same interface they'll return out of. In multi-homed setups this can even be explicit. Load balancers might do the same thing. But even in other less exotic cases internet routers can switch paths dynamically as they rerun the shortest path algorithms, I don't know just how frequently this happens, but it's the reason UDP packets can arrive out of order.

For core switches, you'd be right. But from what I've read, that method could work for routers on the edge of networks. But that's just what I've read, you might well be right ;)


So do you agree that source interface filtering could negatively affect legitimate users?

My guess is it would either work well or not at all. I'm by no means a networking expert though so I'll have to take the lead from someone else.


It's a DNS problem, so I feel that a DNS fix should be used instead of modifying our routers. It's much easier to update dns software than a router. My understanding is that many commercial routers achieve their performance in hardware and become underpowered if too many packets get tossed around into the software stack.

I'd argue it's more a problem with the UDP datagram than DNS specifically. DNS just exposes that weakness of UDP. So if we just fix DNS then I'm sure someone will find another UDP service that can be exploited in the same way (possibly games servers?)

Edited 2013-03-28 16:35 UTC

Reply Parent Score: 2

Soulbender Member since:
2005-08-18

It doesn't seem like source interface filtering is a great solution to me because on the internet there's technically no requirement that packets come in from the same interface they'll return out of


Source filtering makes sure that only packets with a valid source comes in on an interface. Valid source means it's an IP address that has a route via that interface. This is an incredibly simple yet effective way to reduce spoofing on customer-facing equipment and is, as I've said previously, already done by most ISP's.

It's a DNS problem, so I feel that a DNS fix should be used instead of modifying our routers.


While DNS has problems this is not one of them. This is simply a problem of misconfigured DNS servers and the only effective way to stop this from happening is by not screwing up the configuration.

My understanding is that many commercial routers achieve their performance in hardware and become underpowered if too many packets get tossed around into the software stack.


Thankfully not everyone uses underpowered Cisco gear ;)

Reply Parent Score: 2