There are not 13 root servers
I am at the UN Internet Governance Forum, being held this week in Rio de Janeiro, Brazil. A recurring theme you can hear here is one that has vexed the technical community many times before — “Why are there 13 root servers?” This question is usually followed by questions like “Why are most of the root servers in the US?”
So let’s dispel these myths.
There are not 13 root servers.
What there are is there are many hundreds of root servers at over 130 physical locations in many different countries. There are twelve organisations responsible for the overall coordination of the management of these servers.
So where does the 13 number come from?
There is a technical design limitation that means thirteen is a practical maximum to the number of named authorities in the delegation data for the root zone. These named authorities are listed alphabetically, from a.root-servers.net through m.root-servers.net. Each has associated with it an IP address (and shortly some will have more than one as IPv6 is further rolled out).
But when we think of servers, we probably think of physical machines that sit on a desk, or perhaps lined up in racks in a specialised computing facility. By any measure, there are not 13 servers as there is not a correlation between the number of named authorities, and the number of servers.
The majority of named authorities are spread across multiple cities, often multiple countries. The “I” root, for example, is located in 25 different countries. But ignoring the physical diversity, even those authorities that are just in one physical location — the reality is they are comprised of networks of multiple servers that handle the millions of DNS queries the root servers receive every hour.
Another thing you may hear is that some of these root servers are just copies, whilst others are the “real” name servers. The reality is that every single root server is a copy, and none of them are more special than the others. In fact, the true master server from which the copies are made is not one of the public root servers.
So next time you hear there are 13 root servers, or that they are mostly in the US, just remember this map, courtesy of Patrik Fältström: