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Pushback against DDOS Attacks
Huusker writes "Steven Bellovin and others at ATT Research Labs and ICIR have come up with mechanism to stop DDOS attacks. The idea is called Pushback. When the routers get flooded they consult a Unix daemon (/etc/pushbackd) to determine if they are being DDOS'ed. The routers propagate the quench packets back to the sources. The policy and propagation are separate, allowing hardware vendors to concentrate on the quench protocol while the white hats invent ever more clever DDOS detection filters for /etc/pushbackd. The authors of the paper have an initial implementation
on FreeBSD."
If pushback is subverted, couldnt it function like an inverse DOD tool?
That's exactly what this would do. The DDOS'd routers tell their upstream routers to cut back the flow of traffic - basically cutting out the source of the traffic. This of course requires that the upstream routers agree to do this...
SIG: HUP
It would shut off the source of the flood, not the destination as the original poster implied...
SIG: HUP
Nice idea but regex's have waaaay to high an overhead to filter the amount of traffic even a small DDoS produces - you'd need some kind of omnipotent distributed uberBeowulf cluster (or a million monkeys watching a zillion blinkenlights)
DDoS is usually bandwitdh consumption...
Even if you drop 100% of the evil packets...
Your pipe is still filled...
And for the amount of traffic needed to actually DDoS a large-enough site like Yahoo (4 gbps last time around?), RegExs wouldn't be helpful
since, the sheer amount of cpu required to process *every*single*packet*that*passes*through* is wayy too much...
Sounds like a pretty v1.0 idea at this stage, but I'm psyched people are spending brain cycles working on DDoS and flash-flood solutions, since they're both problems that are only going to get worse.
;-)
(Gotta love the Slashdot effect getting named explicitly, eh? Nice to be part of the problem for a change... hehe.)
Seems to me the tricky part here is defining the aggregates. After reading the article, it isn't *really* a way to save your site from going down due to overload, more a way to prevent others sharing your pipe/routers from going down with you.
Which is a good goal in itself. It seems like a real tough thing to determine which of the millions of hits to www.yahoo.com (for ex.) are valid users, and which are DDoS bots. So both get restricted (net result: bots win), but the guy in the cage next to yahoo stays up.
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educate people who are getting infected? Come on. Your not serious...
These people think that when they install virus scan software they are safe. I recently re-installed Windows on my gf's computer. She had V-Shield on there from 1999. She had no idea that she would need to update it.
At least my roommate, my parents, and my gf know (from me) not to open attachments. But educate a WIDE group of people? That's just not going to happen and you know it.
Not all DDoS attacks are bandwidth based, they could be application level and targeted at all sorts of other resources.
.. it would be nice if these actions could be initiated in other situations also.
Some examples:
SYN floods can exhaust incoming connection queues.
DNS floods (asking a recursive nameserver a million questions, or even asking an authoritative nameserver a million questions).
Too many HTTP requests to processor intensive dynamic content pages could deny service well before you are serving at your bw limit.
The paper kept referring to the aggregate detection algorithm only coming into effect when the bandwidth limit is being exceeded
Never the less, this is a promising initiative.
--Iain
that has to be one of the least constructive, head in the sand arguments I've ever read. Did you read the article ?
The technique is about making the internet move the point of dropping the flood packets, BACK closer to the source. That is, remove the flood from the internet itself, and contain it into the localised areas.
Instead of expecting the impossible as you suggest, (which is joe-average running a secure system), finally someone is thinking about securing the internet in general from unsecured systems, which is a pragmatic approach which may well protect the internet in general from many unforeseen DDOS attacks, as well as the ones we know about.
How does it prevent a Server from being Slashdotted?
Not exactly...
If every network provider ran this type of a system on their edge routers. Have all the edge routers communicate to distributed servers. Then, when you are being attacked you simply announce the offending IPs involved in the attack. That announcement gets propogated around all the servers which tell the edge devices to filter the traffic. It isn't a reverse flood. It is a way of telling the router closest to the source to start dropping packets.
Forged source IP's should be dropped at the edge already.
What we need is a protocol for sending dynamic filters to cisco routers. I would like to have input/output lists put on an interface that I can later build dynamically. I do it now with my Linux firewalls but it would be nice if I could drop the packets on the far side of my expensive link.
Now I hope and pray that I will But today I am still, just a bill
How is this design proposing to saturate the Internet?
It involves sending a short message back to the routers that are routing the packets to you asking them to "quench" - i.e. filter out and don't route - the offending upstream sources.
The message could propagate as far back as the individual ISPs from which the packets are originating from so that each participant in the attack is cut off.
At least that's what I'm getting from the summary of the story, I could be completely wrong.
How does this really help a DOS attack? The idea behind a DOS attack is to flood a server with so many packets that the server can't keep up and ends up dropping most of the packets. This paper does not provide a solution to this problem. It simply shifts where the packets are being dropped... at a router upstream instead of at the server or router at the edge of the network. The only advantage here is that other servers hanging off the router that aren't being DOSed will be unaffected.
The suggested solution also opens up a potential security hole. If you gained access to a server, it might be possible to send a packet to routers upstream and tell them to throttle bandwidth. This could be a much more effecient way of doing a DOS attack. Now instead of multiple machines on fast connections, all you really need to DOS your favorite website is a 268 and a 300 baud modem.
Yes, but this would also stop most typical script kiddies. Those are the most malicious ones. Lack of maturity combined with lots of "god complex" tend to cause them to do far more damage than a typical hacker/ddos'er. So if you shut them down or reverse dos them, then they get a taste of their own medicine and you get to laugh while they're trying to figure out why their system just took a dive. :)
Back down to earth, it's mega-wicked when good ideas are developed in FreeBSD (or Linux). Developments like these come the closest to the original intents and purposes of open sourced OSes.
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There is a perfect, 100% sure way of stopping spoofed IP's. It is very easy, non-resource intensive and not being used by lazy network admins.
On every edge router you simply need to put an access-list to drop all packets not coming from your netblocks.
Edge routers going to customers you drop incoming packets not coming from your customer assigned IP. Amost EVERY edge device supports this, most support dynamic filters with RADIUS resquests. If you only allow your customers to send you data from their IP address it is impossible for them to be part of a spoofed attack.
Now I hope and pray that I will But today I am still, just a bill
I believe most DDoS attacks have the following in common:
- DDoS zombies generally send packets with forged return addresses, as
doing so greatly complicates attempts both to block packets and to track
down individual zombies.
-
Machines used for DDoS attacks are almost always either corporate PCs
or home PCs connected by DSL/cable. These nodes are single-homed, and
as such packets emanating from them have only one initial route to the
internet.
My question is this - why can't corporate IT people or their counterparts at ISPs reprogram their front-line routers (those that directly connect to individual end-user PCs) to block packets with forged return addresses? Forged addresses typically are either totally illegal or indicate a totally different net or subnet from the actual sender.I can't see any reason why this wouldn't be a good idea - there really isn't any reason for the type of machines mentioned to ever act as true IP routers (as opposed to NATs), and it doesn't seem like this would be either hard or burdensome for the first-line routers to do.
Employing this would mean that DDoSers would be confined to forging return addresses within the zombies' own subnet, which would make both blocking and back-tracking much easier.
It's plain that this isn't done, so there must be a good reason why people much more network savvy than I haven't implemented it - what is it?
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This idea has been hashed to death for years.
The basic implementation has already been done.
What is novel and new about this paper is the suggestion that upstream routers are going to allow any tom, dick and mary to tell them what packets to throttle.
Always ass-uming that the larger switches can actually do this on the scale that is hinted at in the paper.
While issue 1 is specificly a political issue between carriers and customers, one could always point to the ease of which BGP routes are exchanged as an example of how easy this would be to do. Unfortunatly, since we are now talking about something that could effectivly put a transit provider out of business, there is no way issue number 1 will be overcome, unless the router manufactures give me the same kind of filter and ruleset technology I have for BGP. This would allow me to ignore anything I want from anyone, and would have the net affect of the feature being disabled!
as for 2, I'm sure some router manufacture has been touting this type of 'feature' on thier new multi-gig-a-bit MPLS/IP-does-everything-at-once switch. Don't believe it until it's out of the lab, guys. As many times as carriers have been screwed over by these new startups and their 'awsume powerful technology', I'm supprised anyone believes thier line of crap anymore.
It's too bad DDOS attacks don't go on for weeks, then we could use something like RBL to deal with it. Since they are so transitory, blackholing on the fly, (which is basicly what this paper is advocating) would require a lot more thinking about than has been put into this work.
Perhaps, instead of trying to complicate our lives with Yet Another New Protocol, you could simply come up with and IDS concatonation system, that puts together 'lists' of known DDOS sources at the current moment, and put it into a BGP feed... What a concept! Taking 2 technolgies that are known to work, and available to ANYONE that does BGP on the internet, and making it work!
Thank You, Come Again.
While Pushback technology can help the servers to stay online, they literally push the network load off to another branch of the network where it can congest normal networkconnections. For important servers like the nameservers that have been attacked last week - where they (btw) used a similar technique of pushing requests e.g. network data off to another part of the network - this is a good method. But you run the risk of creating congestion somewhere else on the network. So people working upstream from the attacked server will probably suffer from poor accesibility. It's just a choice what you want to sacrifice, either the targetted servers or the people upstream. But i agree this technology is a step forward towards an appropriate security answer to DDOS attacks.
Yes, the typical arms race situation applies, but the defenders now have some good weapons at their disposal. If the methods that implement the quench feature is robust and hard to subvert, then it is just the server that needs to be updated. Many techniques could be used to identify the sources of the attacks, including some manual help from the system operators. Over time, the demon could get very good at recognizing attacks bases on heuristics, so changes to the flooding packets or patterns might not help get around the filtering.
Not all denial of service is saturation.
What happens when i spoof that you just DoSed your favorite website? You get cut off from it, and denied service.
Although as far as taking advantage of this sort of thing goes, I'd much rather be able to use an ICMP Redirect to make a DoSnet packet its owner.
Pain lasts, kid. Its how you know you're alive. Sometimes I think this growing up thing is just pain management-TheMaxx
Bellovin came out with this a while ago. It's an interesting concept, but has the following practical drawbacks:
1. All the various vendors would have to implement it.
2. False positives. A new form of DoS would be to generate enough spoofed traffic to trigger this sort of thing -aimed at someone else-. Imagine your outrage when your l33t IRC buddies spoof your IP address block whilst attacking www.slashdot.com - no more imbecilic, outdated "Gee, whiz!" types of posts for you to read.
3. Oftentimes, rate-limiting via CAR, traffic shaping, or other methods consumes more CPU cycles on the routers than simply blocking the offending traffic (assuming this is possible, which depends upon the attack methodology).
The best way to combat DoS attacks generally is use strong platforms which process ACLs and other features in hardware (ensuring that your config allows those features to be processed in hardware; logging ACLs like a 'deny ip any any log' just won't cut it, these days), ensure you have the ability to 'draw off the poison' by sinkholing traffic headed for the destination by advertising a null route for it on a sinkhole router (this isn't always possible, it depends upon the target of the attck; you may not want to sinkhole all requests to your Web server, for example), ensure you have as good a traffic sniffing/IDS-type capability as possible, make use of Netflow tools like CAIDA cflowd/OSU flow-tools/Flowscan/Panoptiis/FLAVIO/Arbor Networks' Peakflow DoS, and know how to get in touch with the folks at your ISP(s) who can help with identifying the (even spoofed, via Netflow tracing) sources and blocking the offending traffic upstream of you.
If you're a commercial site, strongly consider a distributed Web site, hosted at different locations and using some sort of Global Server Load Balancing technology (GSLB; Cisco's Distributed Director and 4480 are two examples of this) to send people to different sites depending up their location, network topology-wise.
in a press release by the Office of Homeland Defense, it was announced that an insidious plot by hacker terrorists had been thwarted. It seems that this subversive web site, www.slashdot.org, would trigger random DDOS attacks on targets identified on their web site. It has yet to be ascertained what their intent was, as no logical pattern has been detected. The investigation continues.
Welcome to the Twilight Zone.
I certainly hope the filters used to detect true DDOS attacks are effective enough to prevent this scenario.
An effective solution has to identify the source nodes causing the trouble and block them, not the target. This is hard, but not impossible. The big problem is doing it for fake source IP addresses.
It may be necessary to view routing the way we now have to view mail forwarding - open relays get blocked. If a router isn't sure of the IP addresses of its input, it shouldn't be forwarding those packets. Routers that continue to do so may find themselves blocked.
Yes, because no one is so unethical that they would specify your ip address as the source instead of theirs.
The only thing to slow this down is checking routes, but even that can be gotten around (they just have to be on your network, thats not hard for colo's, shells, and most other providers)
Pain lasts, kid. Its how you know you're alive. Sometimes I think this growing up thing is just pain management-TheMaxx
Most of the reasons why have been said before but to sum it up...
Sending quench packets back to the routers feeding you DDoS packets, and eventually back to the host in question, is a good idea in theory. Kinda like communism. But in practice it won't work. First of all, there are the CPU strain resources on the routers and hosts. With DDoS, you have thousands if not more hosts all banging on your router, and your router is going to get a cardio workout going through its tables and deciding what gets throttled. Secondly, the return addresses on DDoS zombie packets are forged a good 80% of the time, meaning that you'll probably only hit 2 or 3 routers upstream with your quench packets.
A better solution? Null routes come to mind, but there are the CPU issues again. I'd like to see some "technology" similar to this where a customer of a commercial ISP could modify firewall rules on the _ISP's_ router to control traffic coming into their netblock. Perhaps a few routers upstream too. This really appears to be the only logical "quick fix" at the network level for DDoS.
A better fix would be to keep those zombies from ever coming into play by nuking everyone's NT/XP boxes, but that'll have to wait until penguins or daemons rule the planet.
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