Authoritative Name Servers are an important part of the domain name system (DNS); they provide the necessary resolution from a user friendly name like google.com to its IP address. Should a name server fail, this resolution cannot happen and visitors will not be able to visit your site. If you have more than one name server, the requester will try to contact your other name servers if one fails. Having at least two name servers is crucial.
The number of name servers you have for your domain name is important for various reasons that include redundancy, availability and also performance. The most popular value of two name servers is good enough for most small websites, but as our data shows, domain names with higher traffic tend to prefer more than two name servers. As your site grows older and starts receiving more traffic, two name servers will probably be not enough.
Some key findings of our study are as follows. The data consisted of several hundred thousand domain names from across the world.
- The mode (most common value) of the number of name servers is 2. More than 50% of domain names in our data have two name servers. This is expected as most shared hosting companies provide two name servers.
- The median (mid value) of the number of name servers is also 2.
- The mean (average) number of name servers is 2.37.
- A small percentage (0.4%) of domain names have only 1 name server.
- As the traffic increases, domain names tend to have more name servers.
- As the Google PageRank increases, domain names tend to have more name servers
The histogram below shows the distribution of the number of name servers. The X axis is the number of name servers and the Y axis is the logarithm of the number of domain names.
Number of Name Servers and Traffic
As your site gets more established and your number of visitors increase, you also have to think about scaling issues. The density of the number of visitors per minute is an important factor to think about. If you have a fairly large visitor volume, you have to avoid issues with network congestion. By load balancing across several name servers, you can improve the availability and fault tolerance of your site.
Alexa (from Amazon) is a web statistics company that ranks websites based on their traffic. At the micro scale, the rankings might not look accurate, but at a higher level, it gives a fairly accurate view of the amount of traffic that a website receives. The ranking is a number; the lower the ranking, the higher the traffic that the site receives. The following plot of Alexa ranking to the number of name servers shows what one might expect. The number of name servers increases as the ranking improves and the change is most prominent as the ranking goes below 10000. (The chart is a moving average plot with a bucket size of 500).
Number of Name Servers and Page Rank
PageRank is a Google’s algorithm to measure the authority of a site. It is a logarithmic scale, and it is given from 0 to 10 in increments of 1. The higher the page rank, the more authoritative the page. Higher PageRank domain names are usually older, more established sites with several other websites linking to them.
I plotted the number of name servers to PageRank and the results were as expected. More established sites with a higher PageRank tend to use a higher number of name servers.
So, how many name servers should you have?
RFC 2182 recommends that you have at least three name servers.
It is recommended that three servers be provided for most organisation level zones, with at least one which must be well removed from the others. For zones where even higher reliability is required, four, or even five, servers may be desirable. Two, or occasionally three of five, would be at the local site, with the others not geographically or topologically close to the site, or each other.
If you have a small site with an Alexa ranking greater than 100,000, two name servers (with different IP addresses and on different servers at different locations) should be enough. Three should be enough for most sites, though if your Alexa ranking is below 10,000, consider having more. If you are really serious about your DNS infrastructure consider a managed DNS solution that provides Anycast. Most managed DNS providers will not only provide a higher number of name servers, but will also give you a geo-distributed AnyCasted DNS solution which will help reduce your sites’ latency significantly.
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