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A computer network comprises a group of computers and various networking devices connected to share resources and information. An address, known as an IP address, is used to identify every computer and networking device in such a setup. 

An IP address has two parts; the host and network addresses. The network address shows the subnet where the computer or the networking device is located. 

Communication between different machines in an interconnected network happens through various paths. Routing is the process of determining the best communication path based on some preset rules. 

Routing allows data exchange between various devices in a computer network. A router receives a packet of data and determines the destination address. 

What is Anycast Routing?

Anycast is a technology that offers multiple routing paths to a set of endpoints that are each assigned the same IP address. This network addressing and routing method allows incoming requests routed to various nodes or locations.

Through the anycast network routing, all the incoming connection requests are routed across multiple data centers. Anycast network uses some prioritization methodology to distribute data whenever requests come to an IP address associated with the network. 

The choice of data centers is optimized to reduce latency. Anycast will choose a data center with the shortest distance from the requester. Anycast has a 1-to-1 of many associations. 

Uses of Anycast

#1. Content Delivery Network (CDN)

Content Delivery Networks are networks of servers distributed globally whose role is delivering web content to users. Examples of content delivered by such networks are images, videos, audio files, and texts. 

Anycast is used by CDN providers to route users to the closest available server edge. These edge servers offer reverse proxy, static content caching, and OTT for streaming media services.

Users are routed to the next closest location if one location goes offline due to maintenance, crashing, or upgrades. Such a setting improves the general user experience and reduces latency. 

#2. Domain Name System (DNS)

DNS is a process where the internet system converts human-readable domain names to IP addresses. DNS exists in two categories; Recursive DNS providers and Authoritative DNS servers. 

Recursive DNS providers program the IP addresses of the DNS servers directly into the users’ computers, smartphones, watches, and tablets. All the queries such users make using these devices to look up domains are sent to the provider’s servers. 

DNS providers can ensure increased performance and security by managing every end user’s lookup request. 

#3. Hybrid and Multi-Cloud infrastructure

Most modern businesses are built on hybrid cloud infrastructure. Some businesses rely on multiple cloud providers, such as Azure, Amazon, and Google. Anycast can ensure that the end users of businesses using hybrid cloud infrastructures never experience downtimes. 

Users are routed to a cloud location closest to them when Anycast is used in deployment. Such a setting ensures all users connect to the same IP address and also reduces latency. If the current server location fails, users are quickly routed to the closest next available server location. 

#4. Overlay Networks 

Many cloud service providers now offer cloud-based overlay network services to help organizations increase security and control access to the cloud infrastructure and their data centers. Such organizations avoid incurring the high cost associated with building a physically-connected network. 

Overlay networks should be characterized by low latency to serve companies looking for cloud solutions. Anycast routing offers a solution as it ensures a single IP address where remote users across the globe are connected to an overlay network entry point closest to them. 

#5. Network Load Balancing 

Anycast does network load balancing, where it distributes network traffic across multiple servers. Such a setting ensures that no single server will be overwhelmed with too much traffic, eventually improving scalability and reliability. Take a scenario where you have servers A and B.

If server A has downtimes due to damage or attack, the traffic will be routed to server B as they have the same IP address. 

Benefits of Anycast

  • Fast connectivity. Anycast does not use many internet hops and provides a more direct approach when reaching an intermediary node.
  • High availability. Multiple nodes advertise a single IP address, offering redundancy. Thus, a backup is always available when one node fails or becomes overloaded. 
  • Easy setup. One DNS server configuration is enough when you are dealing with Anycast. This server is then distributed to each node on your network. 
  • DDoS protection.

Downsides of Anycast

  • High maintenance costs. Setting up Anycast and managing route announcements can be costly. 
  • Technical to deploy. Setting up Anycast is somehow technical. You also need a certain skill level to manage it effectively. 

Anycast vs. Unicast

Anycast is not the only network addressing and routing option available. We also have Unicast.

In Unicast, individual IPs are assigned to a single node. Thus, static routes are used to connect senders and receivers. In this setting, irrespective of the origin, a single request is always routed along the same path. 

PurposeMost are used for network services that benefit from high availability. DNS and CDN are examples of such services. Suitable for traditional client-server communication. Each device in such a setup communicates with a specific / sends requests to a server. 
Address AssignmentDifferent devices in the Anycast network are assigned the same IP address. Requests are sent to the nearest device on the network. Every device on the network is assigned a unique IP address. All requests follow a specific path where a certain device can only send data to a specific server. 
ScalabilityAnycast distributes requests across different devices on the network. Such an approach makes it easy to scale the network, as no device will be overloaded. Every device on the network communicates only with a specific server. If one of the devices experiences an increase in traffic/ requests, there is no mechanism to make the network more efficient. 

What are DDoS attacks? 

Web servers are designed to handle a specified number of requests at any time. If the number of requests to a network resource or server exceeds these limits, the server will likely halt and prevent new requests from being serviced. 

Distributed Denial of Service (DDoS) attack is when attackers flood a target network with malicious traffic, making it unavailable for users. DDoS attackers use a ‘botnet’ to deliver huge traffic volumes.

The attacker basically creates a system of “zombie networks” after compromising remote devices via techniques such as social engineering

Once the system is infected, these “zombie networks” are instructed to launch an attack, overwhelming the server. 

There are various reasons why malicious people might launch DDoS attacks. In the past, attackers were mainly focusing on ruining the reputation of the target company or causing a disruption of services. However, modern attackers are profiteering from such attacks by requesting monetary compensation to stop the attacks. 

How Anycast reduce DDoS attacks?

Anycast is one of the solutions that can help reduce DDoS attacks. Anycast spreads all the incoming requests across various servers/ different locations. Thus, targeting a specific server and making it unavailable is impossible when the incoming traffic is distributed across different locations. 

During a DDoS attack, Anycast can use the following techniques;

  • Traffic shaping. This technique controls the network traffic flow to ensure it meets the quality of service requirements. Such an approach ensures that the critical applications receive the most bandwidth
  • Traffic redirects. Traffic from the attackers is redirected to different nodes, making it hard to overload one server and make it unavailable. 
  • Rate limiting. This technique limits the rate at which incoming traffic is processed over a server or a network. If a DDoS attack is identified, the rate can be increased to allow legitimate traffic to be processed while filtering out malicious traffic. 
  • Traffic filtering. Anycast can identify traffic patterns from specific regions and block them if there are suspicious activities. Such an approach ensures that malicious traffic never gets to the network. 

How to Make Anycast more Effective

Even though Anycast routing is powerful, you can ensure it works better through these tips;

  • Proper Network Design. The first step is to ensure that the nodes are located in the right places if you want to see the effectiveness of Anycast. Other design tips are ensuring that the network infrastructure is scalable and ensuring you pick the right routing protocols. 
  • Beef up security. Anycast is effective in preventing DDoS attacks. However, you can beef up the security of your network by ensuring you have the right security measures in place. Start by working on access control, encrypting data, and adding firewalls on your systems. 
  • Monitor. Monitoring the performance of your Anycast system makes it easy to detect unusual patterns and take action. The monitoring and reporting processes should be automated.
  • Geographical diversity. Placing your nodes in different regions is a perfect approach to make Anycast more effective. Users’ requests will always be directed to a node near them, resulting in fast processing. 


On top of the other use cases, Anycast is also one of the many approaches that can be used to reduce DDoS attacks. The effectiveness of the Anycast network diffusion approach will depend on factors such as the network size and attack size. 

An extensive network with many distributed servers is likely more effective in diffusing DDoS attacks than a smaller network. Anycast’s role is preventive as it sends network requests to different locations, reducing the impact of a DDoS attack. 

You may also explore top cloud-based DDoS protection for small to enterprise websites.

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  • Titus Kamunya
    Titus is a Software Engineer and Technical Writer. He develops web apps and writes on SaaS, React, HTML, CSS, JavaScript, Ruby and Ruby on Rails

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