Anycast: Internet Optimization and Resilience
27/11/2024
Anycast routing is a key networking technique that allows multiple physical locations to share the same IP address, which means that traffic can be directed to the server that is either geographically closest or offers the user the best possible route. This approach is particularly effective for applications that require high availability, low latency, and resilience, such as DNS servers and content distribution networks. Because it improves speed, redundancy, and reliability, Anycast is an essential option for services that prioritize connectivity quality and efficiency.
The benefits of Anycast routing. The recent LACNIC 42 LACNOG 2024 event included a presentation on the benefits of Anycast routing and how it can be applied to increase DNS resilience and scalability. Carlos Martínez explained that understanding this technique starts with understanding the two key pillars that support the Internet’s operation: routing, which uses the Border Gateway Protocol (BGP), and name resolution, managed by the Domain Name System (DNS).
What is the DNS? The DNS is often referred to as ‘the phone book of the Internet.’ It allows mapping domain names to IP addresses using a distributed data structure in the form of an inverted tree. DNS zones, the equivalent of the phone book’s ‘pages’, contain specific records for each domain. These records are organized in authoritative servers that hold precise information on every zone record, and recursive servers that look up names in this directory.
The role of BGP: the glue that binds the Internet together. Martínez compared BGP to the ‘glue’ that binds the Internet together, as it allows the interconnection of autonomous networks (ASNs) through communication sessions where routing information is exchanged. A critical feature of BGP is its ability to select the best path for traffic between different autonomous systems. This process is based on the analysis of twelve route attributes in a predefined order to ensure the best possible connectivity. The most common attributes include Local Preference, AS Path, and the MED (Multi-Exit Discriminator), which determine the route that will be installed in each router’s final routing table.
When combined with BGP and DNS capabilities, Anycast routing not only optimizes network infrastructure but also enhances the performance, scalability, and resilience of Internet services.
Challenges in DNS scaling and Anycast routing. When deployed on a large scale, DNS routing and other services present several critical challenges. For example, authoritative zone servers can become capacity bottlenecks, risking saturation and creating single points of failure. When servers are located far from users, latency increases and the infrastructure becomes vulnerable to denial-of-service attacks, particularly since DNS zones typically rely on a limited number of authoritative servers. This is where Anycast comes in as a highly effective routing strategy.
Anycast: optimization and redundancy in DNS routing. Anycast allows multiple servers or globally distributed network points to share the same IP address. Rather than a single authoritative server for each domain, multiple servers use the same IP address, and this allows BGP (Border Gateway Protocol) to direct traffic to the nearest or best-located server. This not only optimizes response times, but also provides redundancy and ensures a more balanced load distribution.
In this system, routers receiving BGP advertisements select the best path at any given moment, and IP packets flow without ‘knowing’ that there are several potential destinations behind the same IP address. Under normal conditions, Anycast allows users to connect automatically to the geographically closest server, thus reducing the load on each server.
In the event of failures or attacks, Anycast configuration offers an additional advantage: if a server becomes unavailable —whether due to operational issues or an attack— its BGP advertisement disappears and the traffic it previously handled is automatically redirected to other available servers. This automatic rerouting protects service continuity and strengthens network resilience against incidents.
Conclusion
Implementing Anycast routing not only optimizes network infrastructure, but also significantly improves the resilience, scalability, and performance of critical Internet services such as DNS. When combined with BGP and DNS capabilities, this technique achieves faster, more efficient, and more secure solutions to global connectivity needs.
Click here to watch a recording of the presentation.