It was a scorching Monday on July 22 as temperatures soared above 37°C (99°F) in Austin, TX, the live music capital of the world. Only hours earlier, the last crowds dispersed from the historic East 6th Street entertainment district. A few blocks away, Cloudflarians were starting to make their way to the office. Little did those early arrivers know that they would soon be unknowingly participating in a Cloudflare time honored tradition of dogfooding new services before releasing them to the wild.
6th East Street, Austin Texas
Dogfooding is when an organization uses its own products. In this case, we dogfed our newest cloud service, Magic Transit, which both protects and accelerates our customers’ entire network infrastructure—not just their web properties or TCP/UDP applications. With Magic Transit, Cloudflare announces your IP prefixes via BGP, attracts (routes) your traffic to our global network edge, blocks bad packets, and delivers good packets to your data centers via Anycast GRE.
We decided to use Austin’s network because we wanted to test the new service on a live network with real traffic from real people and apps. With the target identified, we began onboarding the Austin office in an always-on routing topology.
In an always-on routing mode, Cloudflare data centers constantly advertise Austin’s prefix, resulting in faster, almost immediate mitigation. As opposed to traditional on-demand scrubbing center solutions with limited networks, Cloudflare operates within 100 milliseconds of 99% of the Internet-connected population in the developed world. For our customers, this means that always-on DDoS mitigation doesn’t sacrifice performance due to suboptimal routing. On the contrary, Magic Transit can actually improve your performance due to our network’s reach.
Cloudflare’s Global Network
Now that we’ve completed onboarding Austin to Magic Transit, all we needed was a motivated attacker to launch a DDoS attack. Luckily, we found more than a few willing volunteers on our Site Reliability Engineering (SRE) team to execute the attack. While the teams were still assembling in multiple locations around the world, our SRE volunteer started firing packets at our target from an undisclosed location.
Without Magic Transit, the Austin office would’ve been hit directly with the packet flood. Two things could have happened in this case (not mutually exclusive):
Austin’s on-premise equipment (routers, firewalls, servers, etc.) would have been overwhelmed and failed
Austin’s service providers would have dropped packets that exceeded its bandwidth allowance
Both cases would result in a very bad day for everyone.
Cloudflare DDoS Mitigation
Instead, when our SRE attacker launched the flood the packets were automatically routed via BGP to Cloudflare’s network. The packets reached the closest data center via Anycast and encountered multiple defenses in the form of XDP, eBPF and iptables. Those defenses are populated with pre-configured static firewall rules as well as dynamic rules generated by our DDoS mitigation systems.
Static rules can vary from straightforward IP blocking and rate-limiting to more sophisticated expressions that match against specific packet attributes. Dynamic rules, on the other hand, are generated automatically in real-time. To play fair with our attacker, we didn’t pre-configure any special rules against the attack. We wanted to give our attacker a fair opportunity to take Austin down. Although due to our multi-layered protection approach, the odds were never actually in their favor.
Generating Dynamic Rules
As part of our multi-layered protection approach, Dynamic Rules are generated on-the-fly by analyzing the packets that route through our network. While the packets are being routed, flow data is asynchronously sampled, collected, and analyzed by two main detection systems. The first is called Gatebot and runs across the entire Cloudflare network; the second is our newly deployed DoSD (denial of service daemon) which operates locally within each data center. DoSD is an exciting improvement that we’ve just recently rolled out and we look forward to writing more about its technical details here soon. DoSD samples at a much faster rate (1/100 packets) versus Gatebot which samples at a lower rate (~1/8000 packets), allowing it to detect even more attacks and block them faster.
The asynchronous attack detection lifecycle is represented as the dotted lines in the diagram below. Attacks are detected out of path to assure that we don’t add any latency, and mitigation rules are pushed in line and removed as needed.
Multiple packet attributes and correlations are taken into consideration during analysis and detection. Gatebot and DoSD search for both new network anomalies and already known attacks. Once an attack is detected, rules are automatically generated, propagated, and applied in the optimal location within 10 seconds or less. Just to give you an idea of the scale, we’re talking about hundreds of thousands of dynamic rules that are applied and removed every second across the entire Cloudflare network.
One of the beauties of Gatebot and DoSD is that they don’t require a traffic learning period. Once a customer is onboarded, they’re protected immediately. They don’t need to sample traffic for weeks before kicking in. While we can always apply specific firewall rules if requested by the customer, no manual configuration is required by the customer or our teams. It just works.
What this mitigation process looks like in practice
Let’s look at what happened in Austin when one of our SREs tried to DDoS Austin and failed. During one of the first attempts, before DoSD had rolled out globally, a degradation in audio and video quality was noticed for Austin employees on video calls for a few seconds before Gatebot kicked in. However, as soon as Gatebot kicked in, the quality was immediately restored. If we hadn’t had Magic Transit in-line, the degradation of service would’ve worsened until the point of full denial of service. Austin would have been offline and our Austin colleagues wouldn’t have had a very productive day.
On a subsequent attack attempt which took place after DoSD was deployed, our SRE launched a SYN flood on Austin. The attack targeted multiple IP addresses in Austin’s prefix and peaked just above 250,000 packets per second. DoSD detected the attack and blocked it in approximately 3 seconds. DoSD’s quick response resulted in no degradation of service for the Austin team.
What We Learned
Dogfooding Magic Transit served as a valuable experiment for us with lots of lessons learned both from the engineering and procedural aspects. From the engineering aspect, we fine-tuned our mitigations and optimized routings. From the procedural aspects, we drilled members of multiple teams including the Security Operations Center and Solution Engineering teams to help refine our run-books. By doing so, we reduced the onboarding duration to hours instead of days in order to assure a quick and smooth onboarding experience for our customers.
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Today we’re excited to announce Cloudflare Magic Transit. Magic Transit provides secure, performant, and reliable IP connectivity to the Internet. Out-of-the-box, Magic Transit deployed in front of your on-premise network protects it from DDoS attack and enables provisioning of a full suite of virtual network functions, including advanced packet filtering, load balancing, and traffic management tools.
Magic Transit is built on the standards and networking primitives you are familiar with, but delivered from Cloudflare’s global edge network as a service. Traffic is ingested by the Cloudflare Network with anycast and BGP, announcing your company’s IP address space and extending your network presence globally. Today, our anycast edge network spans 193 cities in more than 90 countries around the world.
Once packets hit our network, traffic is inspected for attacks, filtered, steered, accelerated, and sent onward to the origin. Magic Transit will connect back to your origin infrastructure over Generic Routing Encapsulation (GRE) tunnels, private network interconnects (PNI), or other forms of peering.
Enterprises are often forced to pick between performance and security when deploying IP network services. Magic Transit is designed from the ground up to minimize these trade-offs: performance and security are better together. Magic Transit deploys IP security services across our entire global network. This means no more diverting traffic to small numbers of distant “scrubbing centers” or relying on on-premise hardware to mitigate attacks on your infrastructure.
We’ve been laying the groundwork for Magic Transit for as long as Cloudflare has been in existence, since 2010. Scaling and securing the IP network Cloudflare is built on has required tooling that would have been impossible or exorbitantly expensive to buy. So we built the tools ourselves! We grew up in the age of software-defined networking and network function virtualization, and the principles behind these modern concepts run through everything we do.
When we talk to our customers managing on-premise networks, we consistently hear a few things: building and managing their networks is expensive and painful, and those on-premise networks aren’t going away anytime soon.
Traditionally, CIOs trying to connect their IP networks to the Internet do this in two steps:
Source connectivity to the Internet from transit providers (ISPs).
Purchase, operate, and maintain network function specific hardware appliances. Think hardware load balancers, firewalls, DDoS mitigation equipment, WAN optimization, and more.
Each of these boxes costs time and money to maintain, not to mention the skilled, expensive people required to properly run them. Each additional link in the chain makes a network harder to manage.
This all sounded familiar to us. We had an aha! moment: we had the same issues managing our datacenter networks that power all of our products, and we had spent significant time and effort building solutions to those problems. Now, nine years later, we had a robust set of tools we could turn into products for our own customers.
Magic Transit aims to bring the traditional datacenter hardware model into the cloud, packaging transit with all the network “hardware” you might need to keep your network fast, reliable, and secure. Once deployed, Magic Transit allows seamless provisioning of virtualized network functions, including routing, DDoS mitigation, firewalling, load balancing, and traffic acceleration services.
Magic Transit is your network’s on-ramp to the Internet
Magic Transit delivers its connectivity, security, and performance benefits by serving as the “front door” to your IP network. This means it accepts IP packets destined for your network, processes them, and then outputs them to your origin infrastructure.
Connecting to the Internet via Cloudflare offers numerous benefits. Starting with the most basic, Cloudflare is one of the most extensively connected networks on the Internet. We work with carriers, Internet exchanges, and peering partners around the world to ensure that a bit placed on our network will reach its destination quickly and reliably, no matter the destination.
An example deployment: Acme Corp
Let’s walk through how a customer might deploy Magic Transit. Customer Acme Corp. owns the IP prefix 203.0.113.0/24, which they use to address a rack of hardware they run in their own physical datacenter. Acme currently announces routes to the Internet from their customer-premise equipment (CPE, aka a router at the perimeter of their datacenter), telling the world 203.0.113.0/24 is reachable from their autonomous system number, AS64512. Acme has DDoS mitigation and firewall hardware appliances on-premise.
Acme wants to connect to the Cloudflare Network to improve the security and performance of their own network. Specifically, they’ve been the target of distributed denial of service attacks, and want to sleep soundly at night without relying on on-premise hardware. This is where Cloudflare comes in.
Deploying Magic Transit in front of their network is simple:
Cloudflare uses Border Gateway Protocol (BGP) to announce Acme’s 203.0.113.0/24 prefix from Cloudflare’s edge, with Acme’s permission.
Cloudflare begins ingesting packets destined for the Acme IP prefix.
Magic Transit applies DDoS mitigation and firewall rules to the network traffic. After it is ingested by the Cloudflare network, traffic that would benefit from HTTPS caching and WAF inspection can be “upgraded” to our Layer 7 HTTPS pipeline without incurring additional network hops.
Acme would like Cloudflare to use Generic Routing Encapsulation (GRE) to tunnel traffic back from the Cloudflare Network back to Acme’s datacenter. GRE tunnels are initiated from anycast endpoints back to Acme’s premise. Through the magic of anycast, the tunnels are constantly and simultaneously connected to hundreds of network locations, ensuring the tunnels are highly available and resilient to network failures that would bring down traditionally formed GRE tunnels.
Cloudflare egresses packets bound for Acme over these GRE tunnels.
Let’s dive deeper on how the DDoS mitigation included in Magic Transit works.
Magic Transit protects networks from DDoS attack
Customers deploying Cloudflare Magic Transit instantly get access to the same IP-layer DDoS protection system that has protected the Cloudflare Network for the past 9 years. This is the same mitigation system that stopped a 942Gbps attack dead in its tracks, in seconds. This is the same mitigation system that knew how to stop memcached amplification attacks days before a 1.3Tbps attack took down Github, which did not have Cloudflare watching its back. This is the same mitigation we trust every day to protect Cloudflare, and now it protects your network.
Cloudflare has historically protected Layer 7 HTTP and HTTPS applications from attacks at all layers of the OSI Layer model. The DDoS protection our customers have come to know and love relies on a blend of techniques, but can be broken into a few complementary defenses:
Anycast and a network presence in 193 cities around the world allows our network to get close to users and attackers, allowing us to soak up traffic close to the source without introducing significant latency.
30+Tbps of network capacity allows us to soak up a lot of traffic close to the source. Cloudflare’s network has more capacity to stop DDoS attacks than that of Akamai Prolexic, Imperva, Neustar, and Radware — combined.
Our HTTPS reverse proxy absorbs L3 (IP layer) and L4 (TCP layer) attacks by terminating connections and re-establishing them to the origin. This stops most spurious packet transmissions from ever getting close to a customer origin server.
Layer 7 mitigations and rate limiting stop floods at the HTTPS application layer.
Looking at the above description carefully, you might notice something: our reverse proxy servers protect our customers by terminating connections, but our network and servers still get slammed by the L3 and 4 attacks we stop on behalf of our customers. How do we protect our own infrastructure from these attacks?
Gatebot is a suite of software running on every one of our servers inside each of our datacenters in the 193 cities we operate, constantly analyzing and blocking attack traffic. Part of Gatebot’s beauty is its simple architecture; it sits silently, in wait, sampling packets as they pass from the network card into the kernel and onward into userspace. Gatebot does not have a learning or warm-up period. As soon as it detects an attack, it instructs the kernel of the machine it is running on to drop the packet, log its decision, and move on.
Historically, if you wanted to protect your network from a DDoS attack, you might have purchased a specialized piece of hardware to sit at the perimeter of your network. This hardware box (let’s call it “The DDoS Protection Box”) would have been fantastically expensive, pretty to look at (as pretty as a 2U hardware box could get), and required a ton of recurring effort and money to stay on its feet, keep its licence up to date, and keep its attack detection system accurate and trained.
For one thing, it would have to be carefully monitored to make sure it was stopping attacks but not stopping legitimate traffic. For another, if an attacker managed to generate enough traffic to saturate your datacenter’s transit links to the Internet, you were out of luck; no box sitting inside your datacenter can protect you from an attack generating enough traffic to congest the links running from the outside world to the datacenter itself.
Early on, Cloudflare considered buying The DDoS Protection Box(es) to protect our various network locations, but ruled them out quickly. Buying hardware would have incurred substantial cost and complexity. In addition, buying, racking, and managing specialized pieces of hardware makes a network hard to scale. There had to be a better way. We set out to solve this problem ourselves, starting from first principles and modern technology.
To make our modern approach to DDoS mitigation work, we had to invent a suite of tools and techniques to allow us to do ultra-high performance networking on a generic x86 server running Linux.
At the core of our network data plane is the eXpress Data Path (XDP) and the extended Berkeley Packet Filter (eBPF), a set of APIs that allow us to build ultra-high performance networking applications in the Linux kernel. My colleagues have written extensively about how we use XDP and eBPF to stop DDoS attacks:
At the end of the day, we ended up with a DDoS mitigation system that:
Is delivered by our entire network, spread across 193 cities around the world. To put this another way, our network doesn’t have the concept of “scrubbing centers” — every single one of our network locations is always mitigating attacks, all the time. This means faster attack mitigation and minimal latency impact for your users.
Has exceptionally fast times to mitigate, with most attacks mitigated in 10s or less.
Was built in-house, giving us deep visibility into its behavior and the ability to rapidly develop new mitigations as we see new attack types.
Is deployed as a service, and is horizontally scalable. Adding x86 hardware running our DDoS mitigation software stack to a datacenter (or adding another network location) instantly brings more DDoS mitigation capacity online.
Gatebot is designed to protect Cloudflare infrastructure from attack. And today, as part of Magic Transit, customers operating their own IP networks and infrastructure can rely on Gatebot to protect their own network.
Magic Transit puts your network hardware in the cloud
We’ve covered how Cloudflare Magic Transit connects your network to the Internet, and how it protects you from DDoS attack. If you were running your network the old-fashioned way, this is where you’d stop to buy firewall hardware, and maybe another box to do load balancing.
With Magic Transit, you don’t need those boxes. We have a long track record of delivering common network functions (firewalls, load balancers, etc.) as services. Up until this point, customers deploying our services have relied on DNS to bring traffic to our edge, after which our Layer 3 (IP), Layer 4 (TCP & UDP), and Layer 7 (HTTP, HTTPS, and DNS) stacks take over and deliver performance and security to our customers.
Magic Transit is designed to handle your entire network, but does not enforce a one-size-fits-all approach to what services get applied to which portion of your traffic. To revisit Acme, our example customer from above, they have brought 203.0.113.0/24 to the Cloudflare Network. This represents 256 IPv4 addresses, some of which (eg 203.0.113.8/30) might front load balancers and HTTP servers, others mail servers, and others still custom UDP-based applications.
Each of these sub-ranges may have different security and traffic management requirements. Magic Transit allows you to configure specific IP addresses with their own suite of services, or apply the same configuration to large portions (or all) of your block.
Taking the above example, Acme may wish that the 203.0.113.8/30 block containing HTTP services fronted by a traditional hardware load balancer instead deploy the Cloudflare Load Balancer, and also wants HTTP traffic analyzed with Cloudflare’s WAF and content cached by our CDN. With Magic Transit, deploying these network functions is straight-forward — a few clicks in our dashboard or API calls will have your traffic handled at a higher layer of network abstraction, with all the attendant goodies applying application level load balancing, firewall, and caching logic bring.
This is just one example of a deployment customers might pursue. We’ve worked with several who just want pure IP passthrough, with DDoS mitigation applied to specific IP addresses. Want that? We got you!
Magic Transit runs on the entire Cloudflare Global Network. Or, no more scrubs!
When you connect your network to Cloudflare Magic Transit, you get access to the entire Cloudflare network. This means all of our network locations become your network locations. Our network capacity becomes your network capacity, at your disposal to power your experiences, deliver your content, and mitigate attacks on your infrastructure.
How expansive is the Cloudflare Network? We’re in 193 cities worldwide, with more than 30Tbps of network capacity spread across them. Cloudflare operates within 100 milliseconds of 98% of the Internet-connected population in the developed world, and 93% of the Internet-connected population globally (for context, the blink of an eye is 300-400 milliseconds).
Just as we built our own products in house, we also built our network in house. Every product runs in every datacenter, meaning our entire network delivers all of our services. This might not have been the case if we had assembled our product portfolio piecemeal through acquisition, or not had completeness of vision when we set out to build our current suite of services.
The end result for customers of Magic Transit: a network presence around the globe as soon you come on board. Full access to a diverse set of services worldwide. All delivered with latency and performance in mind.
We’ll be sharing a lot more technical detail on how we deliver Magic Transit in the coming weeks and months.
Magic Transit lowers total cost of ownership
Traditional network services don’t come cheap; they require high capital outlays up front, investment in staff to operate, and ongoing maintenance contracts to stay functional. Just as our product aims to be disruptive technically, we want to disrupt traditional network cost-structures as well.
Magic Transit is delivered and billed as a service. You pay for what you use, and can add services at any time. Your team will thank you for its ease of management; your management will thank you for its ease of accounting. That sounds pretty good to us!
Magic Transit is available today
We’ve worked hard over the past nine years to get our network, management tools, and network functions as a service into the state they’re in today. We’re excited to get the tools we use every day in customers’ hands.
So that brings us to naming. When we showed this to customers the most common word they used was ‘whoa.’ When we pressed what they meant by that they almost all said: ‘It’s so much better than any solution we’ve seen before. It’s, like, magic!’ So it seems only natural, if a bit cheesy, that we call this product what it is: Magic Transit.
Today we announced Cloudflare Magic Transit, which makes Cloudflare’s network available to any IP traffic on the Internet. Up until now, Cloudflare has primarily operated proxy services: our servers terminate HTTP, TCP, and UDP sessions with Internet users and pass that data through new sessions they create with origin servers. With Magic Transit, we are now also operating at the IP layer: in addition to terminating sessions, our servers are applying a suite of network functions (DoS mitigation, firewalling, routing, and so on) on a packet-by-packet basis.
Over the past nine years, we’ve built a robust, scalable global network that currently spans 193 cities in over 90 countries and is ever growing. All Cloudflare customers benefit from this scale thanks to two important techniques. The first is anycast networking. Cloudflare was an early adopter of anycast, using this routing technique to distribute Internet traffic across our data centers. It means that any data center can handle any customer’s traffic, and we can spin up new data centers without needing to acquire and provision new IP addresses. The second technique is homogeneous server architecture. Every server in each of our edge data centers is capable of running every task. We build our servers on commodity hardware, making it easy to quickly increase our processing capacity by adding new servers to existing data centers. Having no specialty hardware to depend on has also led us to develop an expertise in pushing the limits of what’s possible in networking using modern Linux kernel techniques.
Magic Transit is built on the same network using the same techniques, meaning our customers can now run their network functions at Cloudflare scale. Our fast, secure, reliable global edge becomes our customers’ edge. To explore how this works, let’s follow the journey of a packet from a user on the Internet to a Magic Transit customer’s network.
Putting our DoS mitigation to work… for you!
In the announcement blog post we describe an example deployment for Acme Corp. Let’s continue with this example here. When Acme brings their IP prefix 203.0.113.0/24 to Cloudflare, we start announcing that prefix to our transit providers, peers, and to Internet exchanges in each of our data centers around the globe. Additionally, Acme stops announcing the prefix to their own ISPs. This means that any IP packet on the Internet with a destination address within Acme’s prefix is delivered to a nearby Cloudflare data center, not to Acme’s router.
Let’s say I want to access Acme’s FTP server on 203.0.113.100 from my computer in Cloudflare’s office in Champaign, IL. My computer generates a TCP SYN packet with destination address 203.0.113.100 and sends it out to the Internet. Thanks to anycast, that packet ends up at Cloudflare’s data center in Chicago, which is the closest data center (in terms of Internet routing distance) to Champaign. The packet arrives on the data center’s router, which uses ECMP (Equal Cost Multi-Path) routing to select which server should handle the packet and dispatches the packet to the selected server.
Once at the server, the packet flows through our XDP- and iptables-based DoS detection and mitigation functions. If this TCP SYN packet were determined to be part of an attack, it would be dropped and that would be the end of it. Fortunately for me, the packet is permitted to pass.
So far, this looks exactly like any other traffic on Cloudflare’s network. Because of our expertise in running a global anycast network we’re able to attract Magic Transit customer traffic to every data center and apply the same DoS mitigation solution that has been protecting Cloudflare for years. Our DoS solution has handled some of the largest attacks ever recorded, including a 942Gbps SYN flood in 2018. Below is a screenshot of a recent SYN flood of 300M packets per second. Our architecture lets us scale to stop the largest attacks.
Network namespaces for isolation and control
The above looked identical to how all other Cloudflare traffic is processed, but this is where the similarities end. For our other services, the TCP SYN packet would now be dispatched to a local proxy process (e.g. our nginx-based HTTP/S stack). For Magic Transit, we instead want to dynamically provision and apply customer-defined network functions like firewalls and routing. We needed a way to quickly spin up and configure these network functions while also providing inter-network isolation. For that, we turned to network namespaces.
Namespaces are a collection of Linux kernel features for creating lightweight virtual instances of system resources that can be shared among a group of processes. Namespaces are a fundamental building block for containerization in Linux. Notably, Docker is built on Linux namespaces. A network namespace is an isolated instance of the Linux network stack, including its own network interfaces (with their own eBPF hooks), routing tables, netfilter configuration, and so on. Network namespaces give us a low-cost mechanism to rapidly apply customer-defined network configurations in isolation, all with built-in Linux kernel features so there’s no performance hit from userspace packet forwarding or proxying.
When a new customer starts using Magic Transit, we create a brand new network namespace for that customer on every server across our edge network (did I mention that every server can run every task?). We built a daemon that runs on our servers and is responsible for managing these network namespaces and their configurations. This daemon is constantly reading configuration updates from Quicksilver, our globally distributed key-value store, and applying customer-defined configurations for firewalls, routing, etc, inside the customer’s namespace. For example, if Acme wants to provision a firewall rule to allow FTP traffic (TCP ports 20 and 21) to 203.0.113.100, that configuration is propagated globally through Quicksilver and the Magic Transit daemon applies the firewall rule by adding an nftables rule to the Acme customer namespace:
Getting the customer’s traffic to their network namespace requires a little routing configuration in the default network namespace. When a network namespace is created, a pair of virtual ethernet (veth) interfaces is also created: one in the default namespace and one in the newly created namespace. This interface pair creates a “virtual wire” for delivering network traffic into and out of the new network namespace. In the default network namespace, we maintain a routing table that forwards Magic Transit customer IP prefixes to the veths corresponding to those customers’ namespaces. We use iptables to mark the packets that are destined for Magic Transit customer prefixes, and we have a routing rule that specifies that these specially marked packets should use the Magic Transit routing table.
(Why go to the trouble of marking packets in iptables and maintaining a separate routing table? Isolation. By keeping Magic Transit routing configurations separate we reduce the risk of accidentally modifying the default routing table in a way that affects how non-Magic Transit traffic flows through our edge.)
Network namespaces provide a lightweight environment where a Magic Transit customer can run and manage network functions in isolation, letting us put full control in the customer’s hands.
GRE + anycast = magic
After passing through the edge network functions, the TCP SYN packet is finally ready to be delivered back to the customer’s network infrastructure. Because Acme Corp. does not have a network footprint in a colocation facility with Cloudflare, we need to deliver their network traffic over the public Internet.
This poses a problem. The destination address of the TCP SYN packet is 203.0.113.100, but the only network announcing the IP prefix 203.0.113.0/24 on the Internet is Cloudflare. This means that we can’t simply forward this packet out to the Internet—it will boomerang right back to us! In order to deliver this packet to Acme we need to use a technique called tunneling.
Tunneling is a method of carrying traffic from one network over another network. In our case, it involves encapsulating Acme’s IP packets inside of IP packets that can be delivered to Acme’s router over the Internet. There are a number of common tunneling protocols, but Generic Routing Encapsulation (GRE) is often used for its simplicity and widespread vendor support.
GRE tunnel endpoints are configured both on Cloudflare’s servers (inside of Acme’s network namespace) and on Acme’s router. Cloudflare servers then encapsulate IP packets destined for 203.0.113.0/24 inside of IP packets destined for a publicly-routable IP address for Acme’s router, which decapsulates the packets and emits them into Acme’s internal network.
Now, I’ve omitted an important detail in the diagram above: the IP address of Cloudflare’s side of the GRE tunnel. Configuring a GRE tunnel requires specifying an IP address for each side, and the outer IP header for packets sent over the tunnel must use these specific addresses. But Cloudflare has thousands of servers, each of which may need to deliver packets to the customer through a tunnel. So how many Cloudflare IP addresses (and GRE tunnels) does the customer need to talk to? The answer: just one, thanks to the magic of anycast.
Cloudflare uses anycast IP addresses for our GRE tunnel endpoints, meaning that any server in any data center is capable of encapsulating and decapsulating packets for the same GRE tunnel. How is this possible? Isn’t a tunnel a point-to-point link? The GRE protocol itself is stateless—each packet is processed independently and without requiring any negotiation or coordination between tunnel endpoints. While the tunnel is technically bound to an IP address it need not be bound to a specific device. Any device that can strip off the outer headers and then route the inner packet can handle any GRE packet sent over the tunnel. Actually, in the context of anycast the term “tunnel” is misleading since it implies a link between two fixed points. With Cloudflare’s Anycast GRE, a single “tunnel” gives you a conduit to every server in every data center on Cloudflare’s global edge.
One very powerful consequence of Anycast GRE is that it eliminates single points of failure. Traditionally, GRE-over-Internet can be problematic because an Internet outage between the two GRE endpoints fully breaks the “tunnel”. This means reliable data delivery requires going through the headache of setting up and maintaining redundant GRE tunnels terminating at different physical sites and rerouting traffic when one of the tunnels breaks. But because Cloudflare is encapsulating and delivering customer traffic from every server in every data center, there is no single “tunnel” to break. This means Magic Transit customers can enjoy the redundancy and reliability of terminating tunnels at multiple physical sites while only setting up and maintaining a single GRE endpoint, making their jobs simpler.
Our scale is now your scale
Magic Transit is a powerful new way to deploy network functions at scale. We’re not just giving you a virtual instance, we’re giving you a global virtual edge. Magic Transit takes the hardware appliances you would typically rack in your on-prem network and distributes them across every server in every data center in Cloudflare’s network. This gives you access to our global anycast network, our fleet of servers capable of running your tasks, and our engineering expertise building fast, reliable, secure networks. Our scale is now your scale.
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