Anycast DNS vs Unicast DNS
February 2, 2021

Anycast DNS vs Unicast DNS

By Ericsson

What DNS servers mainly translate domain names of websites into IP addresses. Servers communicate among them to identify data’s location of the domains we required to make them accessible. 

To know where your website is hosted, you definitely need a DNS server. Two popular DNS routing models are Unicast DNS and Anycast DNS.

What is Unicast DNS?

With Unicast, only one server stores the IP of the website. Its info is available where that DNS server is situated. No matter the place in the world, users request to visit the website, they have to get to this exact point.

DNS request will go to DNS name servers of users ISP, looking for an answer. If it doesn’t get an answer there, it will go from server to server, searching for one that can answer.

In the case of Unicast, we have just one that can answer. 

Suppose the server that has stored the website data is close to the requester, great! He will get a fast answer. But a user requesting the same website from far away will have to wait much more time to get the same answer from the same name server. 

Advantages of Unicast DNS

  • Unicast means one machine, one IP. So installing unicast is simpler because you have to be worried about the maintenance and proper performance of just one server.
  • Therefore, Unicast is cheaper than Anycast. There are different alternatives, but Unicast is still very used on the Internet for its price.
  • It is a choice for websites that target specific markets and not the whole world. If your business is directed just to Chinese users, you can choose Unicast, a DNS server in such a country, so your website will be easily reachable since it is close to your audience and your budget won’t be affected.

Disadvantages of Unicast DNS

  • If the DNS server that stores your website data gets attacked or crashes, accessibility to your website will be seriously affected.
  • If your business targets potentially people all around the world, Unicast DNS is not the best for you. As explained before, you can’t guarantee the best experience for users located far from your server’s location.

What is Anycast DNS?

Several servers located in different geographical points can provide the same IP through Anycast. DNS information from your domain name is copied on as many servers as you pay to have a better presence.

With Anycast, the closest DNS server will answer the user’s request. If one is down, offline due to maintenance or a different reason, the request will go to the second closest, available DNS server to get the answer, and so on. Then user’s request definitely will be answered faster, and the experience will be better in terms of waiting for a response, loading time, etc.

Advantages of Anycast DNS

  • Faster response time. The faster the servers’ response is, the shorter waiting time and fewer potential clients abandoning your site. 
  • Higher uptime and accessibility. A server can fail, but a whole group of servers rarely, at least not at the same time. Therefore, your site will have higher uptime, and access will be guaranteed for users at any time.
  • Better position on search engines. Positive user experience (short waiting response, fast loading, accessibility, etc.) is considered by search engines to rank better or worse your site.
  • Better security. If one server gets compromised, you will have others to rely on.

Disadvantage of Anycast DNS

  • Having more than one server is clearly more expensive. Depending on your budget, this could be a problem.
  • Configuring all servers takes a bit of extra effort but is worth it.

Conclusion

Anycast is clearly more robust than Unicast. What really defines which is more suitable, it’s your business size and needs.