Figure 14-12 shows how a client request gets to the DNS
resolver, which in turn gets to the primary DNS server.
Figure 14-12 DNS Operation
To understand how DNS works, the following steps walk
through how a client, such as a web browser, asks for a
new website:
Step 1. The user clicks on a link or types a URL for a
site to visit (for example,
https://developer.cisco.com).
Step 2. The browser looks in the local cache to see if
the name can be resolved locally on the client.
Step 3. The browser sends a query to the DNS
recursive resolver in an attempt to resolve the
name. The DNS recursive resolver usually
resides with the Internet service provider, and it
can reply if it has the IP address or pass on the
query to the next resolver in the chain. (There
are public name resolvers, such as Cisco
Umbrella and Google.) Eventually, one of the
resolvers may respond with the IP address.
Step 4. If the DNS resolvers cannot find the IP
address, the browser tries the root name
servers, which in turn forward the query to top-