What is Anycast?

Anycast represents a network addressing and routing technique that enables incoming requests to be directed to multiple diverse locations or “nodes.” Within a content delivery network (CDN), Anycast commonly directs incoming traffic to the closest data center equipped to handle the request effectively. By employing selective routing, an Anycast network demonstrates resilience against high traffic loads, network congestion, and DDoS attacks.

How does Anycast work?

Anycast network routing efficiently directs incoming connection requests to multiple data centers. When requests are sent to a single IP address linked to the Anycast network, the network distributes the data using a prioritization method. The selection process for determining the appropriate data center is usually optimized to minimize latency by choosing the data center closest to the requester. Anycast is known for its ability to establish a one-to-one association with multiple destinations and is considered one of the five primary network protocol methods employed in the Internet protocol.

Why use an Anycast network?

When multiple requests are made simultaneously to a single origin server, it can be overwhelmed by the high volume of traffic, leading to inefficient response times and potential service disruptions. However, by utilizing an Anycast network, the distribution of this load can be optimized. In an Anycast network, the traffic is not solely directed to one origin server but can be distributed across multiple data centers. Each of these data centers houses servers equipped to process and respond to incoming requests effectively. This routing approach ensures that the capacity of the origin server is not exceeded and minimizes service interruptions for clients accessing content from the origin server.

What is the difference between Anycast and Unicast?

The majority of the Internet operates through a routing method known as Unicast. In Unicast, each node on the network is assigned a unique IP address. Unicast is commonly used in home and office networks. However, if a computer connected to a wireless network receives a message indicating that the IP address is already in use, it means there is an IP address conflict occurring because another computer on the same Unicast network is already utilizing the same IP address. In most cases, this is not allowed.

When a Content Delivery Network (CDN) employs a Unicast address, traffic is directly routed to a specific node. This can create a vulnerability when the network experiences a significant surge in traffic, such as during a Distributed Denial of Service (DDoS) attack. Since the traffic is directed straight to a particular data center, it is possible for the location or its supporting infrastructure to become overwhelmed by the traffic, potentially resulting in denial-of-service for legitimate requests.

On the other hand, utilizing Anycast offers a highly resilient network. With Anycast, traffic is directed to the optimal path, allowing for automatic redirection of traffic to a nearby data center even if an entire data center goes offline. This enhances the network’s ability to withstand disruptions and maintain the flow of traffic effectively.

How does an Anycast network mitigate a DDoS attack?

Anycast is an effective tool for mitigating Distributed Denial-of-Service (DDoS) attacks. Once other DDoS mitigation tools have filtered out some of the attack traffic, Anycast comes into play by distributing the remaining attack traffic across multiple data centers. This distribution prevents any single location from being overwhelmed with requests. If the capacity of the Anycast network surpasses that of the attack traffic, the attack is effectively mitigated.

DDoS attacks often utilize compromised computers, known as “zombies” or “bots,” to form a botnet. These machines are spread across the internet and can generate an excessive amount of traffic, overwhelming a typical machine connected through Unicast.

A properly implemented Anycasted Content Delivery Network (CDN) enhances the network’s surface area, allowing each data center of the CDN to absorb unfiltered denial-of-service traffic from a distributed botnet. As the network expands in size and capacity, launching an effective DDoS attack against anyone using the CDN becomes increasingly challenging.

However, establishing a true Anycasted network is not a simple task. It requires a CDN provider to maintain their own network hardware, establish direct relationships with upstream carriers, and fine-tune networking routes to prevent traffic disruptions between multiple locations. Toffs, for example, utilizes Anycast to achieve load balancing without traditional load balancers. For a more detailed understanding, you can refer to Toffs’s blog post on their Anycast implementation.