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What is Round Robin DNS?

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  • Written By: David White
  • Edited By: Niki Foster
  • Last Modified Date: 02 November 2016
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Round Robin DNS (domain name server) is a creative way to lighten the server and bandwidth requirements of hosting websites by using a series of IP addresses. This technique is particularly useful to companies whose websites get a very large number of hits and/or a large number of bandwidth-consuming downloads.

Through a careful series of protocols, companies implement Round Robin DNS by assigning a set number of IP addresses to rotate the responsibility of allowing website users to access the company's website. Think of these IP addresses as A, B, C, and D. When the first user accesses the website, this type of DNS system takes the user to address A. The second user gets taken to address B, and so on. Once A is used, it goes to the back of the line; so the fifth user accesses address A.

The name of the protocol is just a clue as to what actually happens, however. Despite the sequential nature of the example, the IP addresses are not assigned in sequential order. Rather, they get assigned in random order. Like a round robin sports tournament, in which one team plays every other team, Round Robin DNS will, if allowed, assign to one user every IP address available. This does not happen every time, of course, but it is conceivable.

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The users don't see any of this, of course. Every single user who accesses that company's website sees exactly what they're supposed to see. The vast majority of websites display a domain name that is letters, not numbers. With Round Robin DNS, however, one particular IP address doesn't have to accept every single hit. This type of system is routinely used by companies that have multiple versions of the same web page residing on different servers, but individual website owners use the protocol as well for the very same reason.

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anon60098
Post 5

vivek080985,

You add the same RR as many times as you like, ie:

www.example.com. IN A 10.0.0.1

www.example.com. IN A 10.1.1.1

www.example.com. IN A 10.2.2.1

www.example.com. IN A 172.16.0.1

etc.

anon36190
Post 4

I felt really happy after reading this article. This was very easy to understand and very informative. Who ever wrote this you are a rockstar. Keep up such easy understanding articles, so that anyone who reads it can understand. --Varun

vivek080985
Post 3

What is the procedure of Mapping the Different IP addresses on a single DNS.

for example: i have four servers like:

74.53.222.78

74.52.239.39

84.233.215.89

How do I map all the different above IPs on a single DNS.

daisy67
Post 2

What if you turn round robin off? We have turned round robin of so that the second ip is only used if the primary has failed. performing an nslookup brings back the addresses in the desired order on both our DNS servers and those of our ISP. however if an nslookup is performed on a public DNS server or a home ISPs DNS server the results round robin. Why might this be the case and can anything be done?

mcptrainer
Post 1

In one of my books it is written that Round robin allows you to use DNS to help spread the load on a group of servers by allowing you to tie multiple IP hosts to a single resource record. In reading some examples, I have come across two different examples. In one example with several servers with same hostname with different Ip addresses and different A records, when a client queries the server to resolve the host's name, the client receives a list of A resource records in response to query. In another example, it is stated that the client receives the first IP address of list in stored zone. Then in second query, the client receives the second IP

address of list. So client does not receive list but only a single result. How can you explain both examples? Is a list returned or a single result returned? I know that a list applies in case of multihomed computers. When does the single result returned apply?

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