Distributed Architecture

No single server or network can handle all of the DNS queries generated by the Internet. Instead, DNS uses a distributed architecture. Domains and network providers divide the hostname management workload. By dividing the workload between different layers of DNS servers, no single system becomes overwhelmed. There are five main types of DNS servers: root, TLD, primary, secondary, and caching. Each type plays a critical role in dividing the workload and managing hostnames.

Root Servers

The root level DNS servers are the primary source for performing name resolution. The root servers do not store hostnames. Instead, these systems contain pointers to other name servers. For example, if a user wants to look up the hostname hen.chicken.coop then the root server will redirect the query to the top level domain (TLD)servers that manage the coop domain. For reverse lookups, the root servers maintain lists of subnets and servers that manage the subnets.

The number of root-level DNS servers has expanded over time. In September 2005, there were 13 root servers. The official list of servers is maintained at http://www.root-servers.org/. Each of the root servers represents a cluster of systems and not a single host. For example, F.root-servers.org has servers operating in 30 different locations around the world. The distribution and redundancy permits load balancing and mitigates the impact from a DoS attack.