When the inevitable 2AM call happens—”our network is under attack”—what do you do? After running through the OODA loop (1, 2, 3, 4), used communities to distribute the attack as much as possible, mitigated the attack where possible, and now you realist there little you can do locally. What now? You need to wander out on the ‘net and try to figure out how to stop this thing. You could try to use flowspec, but many providers do not like to support flowspec, because it directly impacts the forwarding performance of their edge boxes. Further, flowspec, used in this situation, doesn’t really work to walk the attack back to its source; the provider’s network is still impact by the DDoS attack.
This is where DOTS comes in. There are four components of DOTS, as shown below (taken directly from the relevant draft)—
The best place to start is with the attack target—that’s you, at 6AM, after trying to chase this thing down for a few hours, panicked because the office is about to open, and your network is still down. Within your network there would also be a DOTS client; this would be a small piece of software running on a virtual machine, or in a container, someplace, for instance. This might be commercially developed, provided by your provider, or perhaps an open source version available off of Git or some other place. The third component is the DOTS server, which resides in the provider’s network. The diagram only shows one DOTS server, but the reality any information about an ongoing DDoS attack would be relayed to other DOTS servers, pushing the mitigation effort as close to the originating host(s) as possible. The mitigator then takes any actions required to slow or eliminate the attack (including using mechanisms such as flowspec).
The DOTS specifications in the IETF are related primarily to the signaling between the client and the server; the remainder of the ecosystem around signaling and mitigation are outside the scope of the working group (at least currently). There are actually two channels in this signaling mechanism, as shown below (again, taken directly from the draft)—
The signal channel carries information about the DDoS attack in progress, requests to mitigate the attack, and other meta information. The information is marshaled into a set of YANG models, and binary encoded into CoAP for efficiency in representation and processing. The information encoded in these models includes the typical five tuple sets expanded to sets—a range of source and destination address, a range of source and destination ports, etc.
The data channel is designed to carry a sample of the DDoS flow(s), so the receiving server can perform further analytics, or even examine the flow to verify the information being transmitted over the signal channel.
How is this different from flowspec mitigation techniques?
First, the signaling runs to a server on the provider side, rather than directly to the edge router. This means the provider can use whatever means might make sense, rather than focusing on performance impacting filters applied directly by a customer. This also means some intelligence can be built into the server to prevent DOTS from becoming a channel for attacks (an attack surface), unlike flowspec.
Second, DOTS is designed with third party DDoS mitigation services in mind. This means that your upstream provider is not necessarily the provider you signal to using DOTS. You can purchase access from one provider, and DDoS mitigation services from another provider.
Third, DOTS is designed to help providers drive the DDoS traffic back to its source (or sources). This allows the provider to gain through the DDoS protection, rather than just the customer. DOTS-like systems have already been deployed by various providers; standardizing the interface between the client and the server will allow the ‘net as a whole to push DDoS back more effectively in coming years.
What can you do to help?
You can ask your upstream and DDoS providers to support DOTS in their services. You can also look for DOTS servers you can look at and test today, to get a better understanding of the technology, and how it might interact with your network. You can ask your vendors(or your favorite open source project) to support DOTS signaling in their software, or you can join with others in helping to develop open source DOTS clients.
You can also read the drafts—
Use cases for DDoS Open Threat Signaling
Distributed Denial of Service (DDoS) Open Threat Signaling Requirements
Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel
Each of these drafts can use readers and suggestions in specific areas, so you can join the DOTS mailing list and participate in the discussion. You can keep up with the DOTS WG page at the IETF to see when new drafts are published, and make suggestions on those, as well.
DOTS is a great idea; it is time for the Internet to have a standardized signaling channel for spotting and stopping DDoS attacks.