Anycast is a routing scheme in which a single IP address is applied to several geographically distributed servers. Data packets sent to this IP address reach the nearest or most suitable server. The purpose of this routing scheme improves the efficiency and reliability of data transmission by reducing latency, distributing the load across multiple servers, and increasing resilience. Anycast is often used in services such as DNS, Content Delivery Networks (CDNs), and for DDoS protection.
A routing scheme is a systematic approach to determining the path that data packets take in a network to get from a sender to a receiver. It defines the rules and methods by which data packets are routed through the network to ensure the most efficient and reliable transmission. Routing schemes determine how routers and other network devices process and forward information.
Anycast works by using the same IP address for multiple locations on the network. Multiple servers (nodes) in different geographic locations are configured to share the same IP address. These servers are connected to each other via the Internet or another large network.
BGP (Border Gateway Protocol) is the most commonly used routing protocol for Anycast. Each server with the Anycast address announces this address to the surrounding routers via BGP, which are propagated through the Internet.
When a client sends a request to the Anycast address, the network uses the routing information to decide which route is most suitable. The “best” route is usually the one with the lowest cost or the shortest distance. The network sends the request to the server that is closest according to the routing tables.
The closest server receives the request and processes it. If this server fails or is overloaded, another route to the Anycast address is selected so that the request is processed by another server.
Anycast offers numerous advantages that make it an attractive option for many network services. Lower latency is one of the standout benefits, as requests are sent to the closest server geographically or network-wise, reducing response times and allowing users to get faster responses to their requests. Another benefit is load balancing, where traffic is distributed across multiple servers to reduce the load on individual servers and improve the scalability and performance.
The increased availability and reliability is also a decisive advantage. By distributing traffic across several servers, the failure of one server can be compensated for by other servers, which increases the overall availability of the service and reduces downtime. DDoS protection is another important aspect, as Anycast can help mitigate DDoS attacks by distributing attack traffic across multiple locations. This prevents a single server from being overwhelmed, thereby improving the security of the service.
Another plus point is the simple scaling. New servers can easily be added by adopting the Anycast address and announcing it via BGP, allowing flexible and easy scaling of the infrastructure. Optimized resource utilization is an additional benefit, as requests are sent to the closest server so network bandwidth can be used more efficiently, optimizing the overall network load.
In addition to Anycast, there are several other routing schemes that are used in IP networks.
Unicast
With Unicast, a single source is connected directly to a single receiver. This is the most common form of routing on the Internet. A typical example is communication between a client and a server, e.g., when retrieving a website. Unicast is particularly efficient for point-to-point communication.
Broadcast
Broadcast sends data packets to all devices within a network or subnet. It is used in local area networks (LANs) for tasks such as the Address Resolution Protocol (ARP), where the MAC address of a device is determined. Broadcast reaches all devices on the network and is useful for certain network protocols and services.
Multicast
Multicast sends data packets to a defined group of recipients simultaneously. It is often used for streaming media (audio, video), online games, and other real-time communication services. Multicast is efficient for simultaneous transmission to multiple recipients and saves bandwidth compared to Unicast.
Geocast
Geocast sends data packets to all devices within a specific geographic area. It is used in specialized applications such as geographic information systems (GIS), mobile ad hoc networks, and emergency communication systems to enable targeted communication based on geographic locations.
Anycast is used in various areas and applications to improve the efficiency, reliability and performance of networks. One important area of application is the Domain Name System (DNS), where Anycast is often used by DNS providers to forward queries to the nearest server. This significantly improves response times and increases the reliability of the DNS service.
Content Delivery Networks (CDNs) are another important area of application for Anycast. CDNs use Anycast to forward user requests to the nearest or most suitable server that can provide the requested content. This reduces latency and improves the loading times of websites and other online content.
Anycast also plays an important role in protecting against Distributed Denial of Service (DDoS) attacks. By distributing the attack traffic across several servers, the load on individual servers is reduced, which increases the effectiveness of the defensive measures.
In the area of load balancing, Anycast is used to distribute network traffic evenly across multiple servers. This leads to better resource utilization and ensures higher performance and availability of services. This is particularly important in large data centers that use global server load balancing.
Anycast is also used for IPv6 and transition mechanisms. It is used to increase the availability and efficiency of network connections, especially for IPv4-IPv6 transition mechanisms.
Another area of application for Anycast is the Network Time Protocol (NTP). Anycast is used here to distribute requests for time servers, which improves the accuracy and availability of time services. NTP pools are an example of the use of Anycast in this area.
Finally, Anycast is used in various routing and infrastructure services to improve reliability and performance. Examples of this are root DNS servers and Anycast addresses for routing services. By distributing traffic across multiple servers in different locations, Anycast helps to make these services faster, more robust, and more resistant to outages and attacks.
