Learn About Anycast And Some Of Its Advantages And Disadvantages

The continuing rapid development of internet technology has led to the creation of methodologies which would have seemed unimaginable during the earliest days of online communication. One of those important methods is “Anycast,” which can greatly enhance the speed and reliability of data transmission.

• About Anycast
• Unicast/Anycast/Multicast
• Benefits of Anycast DNS
• Limitations of Anycast DNS
• Getting Started

What Is Anycast?

Anycast is a system utilizing network addresses and routing methods in order to send data to the closest available node within a group of receivers which are using the same IP address. Internet Protocol Version 4 (IPv4) addressing allows a host to determine which of several hosts should receive specific data packets, to facilitate the fastest delivery of information to an end user.

In practical terms, the use of Anycast reduces latency (thereby increasing delivery speed) and helps a provider to balance server loads, while providing “backup” in the event of server failure within the group sharing the IP address.

Unicast vs. Anycast vs. Multicast

The easiest way to understand Anycast is by comparing it to other common methodologies for internet addressing.

• Unicast: this is the most common routing system used on the internet, with every node assigned a unique IP address. Routers identify where data is headed, and determine the shortest path for data packets to take from their point of origin to their destination. The data is handed off between routers until it arrives at its final IP destination. For example, if the data originates from an IP in London and is destined for Los Angeles, the system figures out the best path for the packets and sends them along that path. The process only takes milliseconds but is still dependent on the health of each router in the path, as well as the health of the destination node. Because it simply involves sending data from origin to destination, it is considered a one-to-one association.
• Anycast: the primary logistical difference between unicast and Anycast is that with Anycast, a number of nodes share the same IP address. Rather than determining a single destination for data, the Anycast system first decides which of the nodes with the same IP is closest to the origination point, and then directs the data to that endpoint. Again consider data originating in London, but with nodes in Los Angeles, Hong Kong, and Paris all sharing the same destination IP. The Anycast system first determines that Paris is the closest node to London, and then routes the data there. This drastically reduces the time required for successful data transmission. Another benefit is that if the Paris node is down, the system can simply re-route the data to Hong Kong or London without an issue. Anycast is considered a one-to-nearest association.
• Multicast: this is a different way of routing traffic. Rather than being sent to a specific IP address, multicast traffic is sent to a group of different hosts, with different addresses, at the same time. Nodes which are subscribed to the multicast group are all able to receive the traffic. This protocol is not typically used by internet routers; it is commonly used, for example, within a corporate network in order to deliver traffic without using an enormous amount of bandwidth. Multicast is considered a one-to-unique many associations and is different than broadcast methodology, which allows all of the hosts on a network segment to receive the traffic and is considered a one-to-many association.

What Are The Benefits Of Anycast DNS?

• As mentioned earlier in this article, the three major benefits of using Anycast DNS routing are speed, load balancing, and redundancy. Two other benefits which are nearly as important are easy scalability and better response to DoS and DDoS attacks.
• The fact that Anycast allows connection to the closest DNS server with the requisite IP means that there is usually a significant saving in network latency, meaning a noticeable increase in data delivery speed. Additionally, since a number of different servers are utilized to respond to requests, individual server load is reduced allowing each server to respond faster.
• No client on a network is immune to downtime, and Anycast provides important redundancy for the network. If the closest DNS server is unable to respond to a request, a more distant server can easily pick up the slack meaning better uptime for the network as a whole. This geographical insurance is the most efficient means of operation. It is also easy to see how Anycast lends itself to upscaling a network since it’s simply a matter of adding another node sharing the same IP address; it has been shown to work with hundreds of servers located worldwide.
• Finally, Anycast is able to help a network respond to attacks. DoS or DDoS attacks can easily overwhelm a unicast server; when traffic is spread out across an Anycast network each server absorbs a portion of the attack lessening the possibility of the entire network going down. This is particularly true for most DoS attacks, which usually focus on the node closest to the zombies.

What Are The Drawbacks Of Anycast?

Anycast doesn’t come without flaws. The major concern is that the redundancy it provides isn’t always flawless; it’s possible for a server to partially fail while still showing as “available” on the network, meaning that the network becomes unavailable to those who are geographically closest to the problem. Proper Anycast “heartbeat” functionality, which monitors servers and removes them from the network at any sign of a problem, can mitigate this issue in most cases. Additionally, the investment required is greater than simply using unicast to send and receive data from a single node.

How Do You Get Started With Anycast?

Building an Anycast system is primarily a matter of configuring routers and servers properly, which can be done by specialists with the proper training or knowledge. However, it does also involve possessing or setting up a number of geographically separated nodes in order to send and receive data, and having an assigned IP prefix suitable for Anycast.

Companies wishing to use the Anycast method for their networks also have the option of contracting with a specialized hosting provider to run it on their behalf.