There are 13 root DNS server addresses, but these are implemented on a far larger number of physical servers distributed globally.
The root DNS servers are critical to the function of the Internet's domain name system. They are at the top of the DNS hierarchy and are the first step in resolving domain names to IP addresses.
Understanding the Root DNS Servers
-
The Logical 13: While there are 13 addresses, these are not 13 individual physical servers. Each address (A through M) represents a network of servers located around the world. This network uses a technology called anycast.
-
Anycast: Anycast allows multiple servers to share the same IP address. When a DNS resolver queries a root server address, the request is routed to the closest server geographically or based on network conditions. This greatly improves performance, redundancy, and resilience.
-
Global Distribution: The various root server operators deploy many physical servers around the world, providing a globally distributed infrastructure. This ensures that the DNS root remains accessible even if individual servers or entire regions experience outages. The actual number of physical servers is significantly larger than 13 and constantly changing as capacity is added.
Why 13 Root Server Addresses?
The limitation to 13 root server addresses is a historical artifact of the original DNS design and the maximum size of a UDP packet (the primary protocol used for DNS queries). Fitting more than 13 addresses into a single UDP packet would have introduced complexities. With modern DNS implementations using TCP and larger UDP packets, this limit is less relevant, but changing it would require a massive and potentially disruptive overhaul of the DNS infrastructure. Using Anycast obviates the need to introduce more root server addresses.
Function of Root Servers
Root servers don't contain the answers to all DNS queries. Instead, they point DNS resolvers to the appropriate Top-Level Domain (TLD) name servers (e.g., .com, .org, .net). Those TLD name servers then point to the authoritative name servers for specific domains.
Summary
While the DNS architecture specifies 13 root server addresses, the actual number of physical servers implementing those addresses is far greater and distributed globally for performance and redundancy.
