Root servers are confronted with a large number of requests day in, day out. A large number of the 13 root name servers isn’t simply answered by the clients’ request alone; this is done in cooperation with other servers as well. However, there are far more than simply 13 different servers that take care of the root zone requests; all in all, there are hundreds of such scattered throughout the world that are responsible for this task. Most of the servers are located in the United States or Europe.
The fact that these servers are so spread out helps with load balancing and hence increases the reliability of root servers: before Anycast came along, there were only the 13 main root name servers that were able to take care of answering requests. Given that 10 of these are located in the United States, Anycast technology first made this relatively decentralized request processing in the root zone possible. The worldwide distribution of servers furthermore makes for shorter access times when it comes to processing requests, given that the server always answers these in the shortest ways.
A further security measure in terms of the limits of the used root name server’s capacities during normal operation: only a third of the available computing resources are used by servers. This helps ensure that name resolution can still be carried out when multiple DNS root servers experience shortages: in such cases, the rest of the active servers take on the requests that were actually meant to be sent to the downed server.
Following this, various DDoS attacks on DNS root servers didn’t have any success in the past, as their security set-ups were just too strong. Those operating the 13 root servers know only too well what their servers mean for the internet: without them, addressing internet services is no longer feasible.