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Anycast Routing and its Applications

Last Updated : 31 Oct, 2023
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Anycast routing is a way of sending data over the network to the destination. It has multiple possible locations. For example, suppose you want to access a website that has servers in different countries. Anycast routing can help you connect to the server that is closest and best for you. Instead of sending you to a fixed location, web browsing is faster and more reliable.



  • Anycast routing is different from other types of routing. Such as unicast, multicast, and broadcast.
  • Unicast routing is when data is sent from one source to one destination. Such as when you send an email to a friend.
  • Multicast routing is when data is sent from one source to many destinations. Such as when you watch a live stream online.
  • Broadcast routing is when data is sent from one source to all destinations. such as when you send a message to everyone on a network.
Unicast vs Anycast

Anycast Vs Unicast

Benefits of Anycast Routing

  • Improved performance: Anycast routing can reduce distance and delay between source and destination. So data transmission faster and smoother.
  • Load balancing: Anycast routing can distribute the traffic among multiple servers. So it prevents any single server from being congested.
  • Resilience: Anycast routing can increase availability and reliability of the service. It automatically switching to another server if one server fails and becomes unreachable.
  • Scalability: Anycast routing can easily add and remove servers from the network. It done without affecting the service.

Challenges of Anycast Routing

  • Routing consistency: Anycast routing can cause packets to take different paths. It depends on network conditions and routing protocols. But there can be issue. Such as TCP connections and video streaming.
  • Security: Anycast routing can expose the service to more potential attacks. It increases number of entry points and exit points for the data. This need encryption and authentication.
  • Management: Anycast routing can complicate monitoring and troubleshooting of the network. This needs tools and techniques.

Applications of Anycast routing

  • Content delivery networks (CDNs): CDNs use anycast routing to deliver web content faster and efficiently to users to world. It caches on multiple servers with same anycast address.
  • Domain name system (DNS): DNS uses anycast routing to resolve domain names faster and reliably. It distributes queries among multiple resolvers with the same anycast address.
  • Distributed denial-of-service (DDoS) mitigation: DDoS mitigation services use anycast routing to protect websites and networks from large-scale attacks. It diverts traffic to scrubbing centers with the same anycast address.

Basic Terms

These are important basic terms related to Anycast routing:

1. Anycast Address

This is IP address. It is not unique to one device. It is shared by multiple devices in different locations. For example, suppose there are three web servers with same anycast address: in New Delhi, London, and Mumbai. When you send a request to this address, the routers will direct your packets to the nearest and best web server according to some criteria. These are number of hops, latency, and load. So you can access web content faster and more reliably.

2. Anycast Network

This is a network that supports anycast routing. These two types natively and tunneling techniques. Native anycast network is network that uses anycast routing protocol. It uses to advertise and forward anycast addresses. Whereas, Tunneling anycast network is network that uses unicast routing protocol. It creates tunnels between anycast nodes and then forward anycast addresses to tunnels. For example, suppose there are two DNS resolvers with same anycast address 2001:db8::53 in different continents. Native anycast network would use BGP. It uses to announce and route this address to nearest. Tunneling anycast network would use OSPF to create tunnels between resolvers and then route this address over these tunnels.

3. Anycast Service

This is service. It is provided by multiple nodes in anycast network. Such as web server and DNS resolver. This service improves performance, availability, and scalability. Because it distributes load and traffic among many nodes. It also improves security and resilience. It mitigates DDoS attacks and handling failures and changes in the network topology.

4. Anycast Routing Protocol

This is a protocol. It uses Border Gateway Protocol (BGP) and Open Shortest Path First (OSPF). It advertises and forwards anycast addresses in the network. Metrics such as hop count, bandwidth, and load to select the best path for each packet.

Steps of Anycast Routing


Assigning an anycast address to multiple nodes in a network. These can be statically and dynamically. Each node that provides the same service and function will have the same IP address. This can done manually and automatically assigned by a protocol such as DHCP.


Advertising the anycast address to other nodes in the network. It uses anycast routing protocol. Each node that has the anycast address will announce it to its neighbors. These can use protocol such as BGP2 and OSPF3. This will propagate the information throughout the network.


Forwarding packets sent to the anycast address. It is sent to nearest and best node based on some criteria. These are hop count, latency, bandwidth, and load. When a packet is sent to the anycast address. Routers in the network will use their routing tables and algorithms to determine the best path. It reaches one of the nodes that has the anycast address. Then forward the packet accordingly.


Handling failures and changes in the network topology. It updates the anycast routing protocol. If a node that has the anycast address becomes unavailable and unreachable. Also if a new node joins/leaves the network. Then anycast routing protocol will detect and react to these events. Then update the routing tables and paths accordingly.

Frequently Asked Questions

Q.1: How does anycast routing impact TCP connections?


Anycast can disrupt TCP sessions by sending packets to different nodes.

Q.2: How does anycast routing affect security?


Anycast improves security by spreading traffic but introduces authentication and encryption challenges.

Q.3: How does anycast routing influence scalability?


Anycast enhances scalability by adding/removing nodes dynamically, but data synchronization can be tricky.

Q.4: How does anycast routing impact performance?


Anycast can boost performance by reducing latency but may cause packet issues.

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