Ask Slashdot: Experience Handling DDoS Attacks On a Mid-Tier Site?

New submitter caboosesw writes "A customer of mine recently was hit by a quick and massive DDoS attack. As we were in the middle of things, we learned that there are proxy services of varying maturity to deal with these kinds of outbreaks from the small and mysterious (DOSArrest, ServerOrigin, BlackLotus, DDOSProtection, CloudFlare, etc.) to the large and mature (Prolexic, Verisign, etc.) Have you guys used any of these services? Especially on the lower price point that a small e-commerce (not pr0n or gambling) company could afford? Is a DDoS service really mandatory as Gartner now puts this type of service in the same tier as SEIM, firewalls, IPS, etc?"

Comments

Post-mortem: Admin investigates attack

[microTodd]

Remember this really cool slashdot story about a sysadmin on the receiving end of a DDOS?

http://slashdot.org/story/01/05/31/1330202/post-mortem-of-a-dos-attack

The original writeup link is dead but I found it here (warning: PDF). This was a really cool story.

http://www.stanford.edu/class/msande91si/www-spr04/readings/week1/grcdos.pdf

Re:Load balancing and an experienced sysadmin

[SethJohnson]

watch the attack and start blacklisting IP ranges.

In most cases, your customers are going to exist in one or a few countries. It would be valuable ahead of time to add redirect rules to your iptables for entire ranges of IP addresses located in countries that don't host your customers. Redirect these IP ranges to a sacrificial server on a different pipe to the backbone. That way, when some of your customers are abroad and need access to your services, they can still get some amount of response.

Additionally, you can proactively parse your user accounts for IP addresses and build a whitelist ruleset for your iptables to implement in a defcon 0 situation. Don't use this as a normal operations mode, just when the shit has really hit the fan and you need to block everyone except your known-good account holders.

Seth

Ah, but you CAN do something

[Anonymous Coward]

Even if you knew with 100% certainty which packets were "bad" packets and which were "good" packets, if your uplink is saturated, dropping them on your edge router/firewall/whatever is 100% ineffective.

Your "best strategy" advice is very good, but it is not the "only strategy."

As others have said, you can also have multiple entry points all sharing the same back end. Each of these entry points can be on their own hosting provider. In principle, you can arrange for the front-end/back-end connection at your front-end provider to NOT share a physical wire with the "public" side of your front-end, so if it gets hit hard it crowd out traffic going to/from the back end.

Here's an example:

I run poormeddosvictim.com. I have servers at 3 sites around the country, 1.666.3.4 1.2.666.4, and 1.2.3.666.

For some reason, some mining company on Mars thinks I am evil so they keep DDOSing me.

Hosting provider A is widely connected. I advertise 1.666.3.4 so all but one of A's pipes see direct connections. I use A's remaining pipe to connect back to my back-end. I work with A so the traffic to the back-end never shares a wire or router with incoming traffic. Bang on A's incoming pipes all you want, I'll still be able to talk to my back end unless you crash me entirely.

I have similar arrangements with hosting providers B and C.

I put my back end at hosting provider D and, just for grins, have a backup back end on hosting provider E that syncs up regularly with the back-end on D.

Re:Misunderstanding

[Liquid-Gecka]

This is a bit of a naive explanation.

Let me explain how a DDoS mitigation strategy works for many of the companies listed in the summary. They setup datacenters in 10, 15, or more places all hosting a proxy. Some of these solutions use DNS to route traffic around problems (GSLB) while others like CloudFlare use Anycast which is awesome and super hard to get right. Each of these services are typically setup with tons of bandwidth capacity, well over 10Gb, but often times into the 100Gb range. They also often have deals with upstream providers that can filter traffic at the edges meaning it never makes it onto the internet in the first place.

Since you servers are not exposed to the internet, and the ones are are have far, far more horsepower to deal with this than a DDoS will even manage from the client side they can easily just churn through the attack, discarding connections and never letting them hit your limited servers. This is how they can easily survive Anonymous style DDoS attacks.

The other thing is to ensure you have turned of every "feature" your load balancer is giving you. SSL termination at the LB, full session management, etc. All of these cost load balancer CPU which is easy to take advantage of, even if there is a DDoS mitigation system in front of your site. You can't just add a few more servers either. Adding capacity to a load balancer is nearly impossible to do mid-attack.

Even more interesting is that you can often times trick the crappy ddos software by doing things like excessively slow responses (tarpitting) making its loop take ages to try again. This is pretty much using the tactics of a DDoS directly against the attackers.

Another common tactic is to add attackers to a view in your bind config that resolves your hostname to 127.0.0.1 just for them. This works if you do not have long TTLs and they are using hostnames. If they are using direct IPs then you simply move your traffic to a second IP and drop the one they are attacking. Best case is if you can do this via BGP announcements so the traffic simply will fail to route and everybody wins.

And yes, I do this professionally but not for any commercial product.