Take a suitable DNS-lookup utility (e.g., nslookup) and disable the recursive lookup feature (e.g., with set norecurse), so that when your utility sends a query to a DNS server, and that server is unable to fully answer the request from its own records, the server sends back the next DNS server in the lookup sequence rather than automatically forwarding the query to that next server.
Then carry out manually a name lookup such as that in Figure 9.5; try the host name www.cs.princeton.edu. List each intermediate name server contacted. You may also need to specify that queries are for NS records rather than the usual A records.
Figure 9.5
