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."

Comments

Couldnt pushback be a Dos tool in itslf?

[Anonymous Coward]

If pushback is subverted, couldnt it function like an inverse DOD tool?

Re:Manual RegEx?

[Bill Wong]

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...

Re:sure

[garcia]

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..

[Anonymous Coward]

Not all DDoS attacks are bandwidth based, they could be application level and targeted at all sorts of other resources.

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 .. it would be nice if these actions could be initiated in other situations also.

Never the less, this is a promising initiative.

--Iain

Re:sure

[Anonymous Coward]

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.

Re:sure

[Doug Neal]

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.

This is worse

[greenrom]

What the paper suggests is that if a router is getting way too many packets to a specific destination address, it will tell the routers upstream to throttle packets to that destination address (drop a certain percentage of them).

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.

blocking packets with forged return addresses

[wfmcwalter]

Perhaps someone more network-literate than I can answer this DDoS question, which has bothered me for some time.

I believe most DDoS attacks have the following in common:

1. 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.
2. 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?

Re:blocking packets with forged return addresses

[swb]

"Good" networks prevent forged packets by doing what you suggest, dropping packets with bogus source addresses at the edge of the network or at appropriate ingress points.

I think the argument that is made for not doing this at a lot of ISPs is that with most Cisco routers its expensive as a lot of their routers can't fast switch with ACLs applied, they process switch, turning an adequate router into an inadequate packet-dropper.

It can also be a PITA to maintain -- if you put it at the very edge, like on an ISPs peering router with their upstream, it doesn't prevent in-block spoofing (eg, spoofing packets within the ISPs block). If you try to beat that on all the aggregation routers, you have a lot of ACLs to maintain; customer churn could put address blocks all over the place.

I'd argue that ISPs should make it a term of service that *their* customers ACL their edge routers; we-catch-spoofing-we-cut-you-off language.

Re:Old Idea

[Cato]

A BGP feed will only help if you want to drop ALL traffic to a given IP prefix - the ACC proposal actually lets you limit traffic by port number as well.

Also, a BGP-only solution would only let you drop traffic, so it's not very useful for flash crowds, where the traffic is legitimate but excessive. It's also not useful where the port / prefix etc can't precisely identify only DDoS traffic - rate limiting allows some good traffic to get through while also limiting the DDoS. Blackholing != limiting (did you read the paper at all?)

I agree that this can be prototyped using existing technology (see my post elsewhere), but if this approach proves useful, a dedicated protocol would be helpful - though this could perhaps be piggybacked onto BGP using additional attributes to carry the filter and rate limit information.