DNS on Windows Server 2003, 3rd Edition

Root Name Servers

The root name servers know where the authoritative name servers for each of the top-level zones are. (In fact, some of the root name servers are authoritative for some of the generic top-level zones.) Given a query about any domain name, the root name servers can at least provide the names and addresses of the name servers that are authoritative for the top-level zone the domain name ends in. In turn, the top-level name servers can provide the list of authoritative name servers for the second-level zone that the domain name ends in. Each name server queried either gives the querier information about how to get “closer” to the answer it’s seeking or provides the answer itself.

The root name servers are clearly important to resolution. Because they’re so important, DNS provides mechanisms—such as caching, which we’ll discuss a little later—to help offload the root name servers. But in the absence of other information, resolution has to start at the root name servers. This makes the root name servers crucial to the operation of DNS; if all the Internet root name servers were unreachable for an extended period, all resolution on the Internet would fail. To protect against this, the Internet has 13 root name servers (as of this writing) spread across different parts of the network. One is on PSINet, a commercial Internet backbone; one is on the NASA Science Internet; two are in Europe; and one is in Japan.

Being the focal point for so many queries keeps the roots ...