DNS Name Resolution Process

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You should be familiar with the DNS name resolution process:

 

1. When a DNS name resolution request is forwarded to a DNS server, the DNS server examines its local DNS cache for the IP address.
2. If the IP address is not in the DNS server's cache, it checks its Hosts file. (Since the Hosts file is a static text file, it is not commonly used.)
3. If the DNS server is not authoritative and configured for forwarding, the DNS server forwards the request to a higher-level DNS server.
4. If the DNS server cannot forward the request, or if forwarding fails, the DNS server uses its Root Hints file (also known as Cache.dns). The Root Hints file lists the 13 root DNS servers.
   
5. The root DNS server responds with the address of a com, edu, net, or other DNS server type (depending on the request).
6. The DNS server forwards the request to the high-level DNS server, which can respond with a variety of IP addresses.

You should know the following facts about DNS:

DNS translates a hostname to an IP address.

The DNS hierarchy is made up of the following components:

• . (dot) domain (also called the root domain)
• Top Level Domains (TLDs) (.com, .edu, .gov)
• Domains
• Hosts

1. A fully qualified domain name (FQDN) must include the name of the host and the domain, not just the domain.
2. A forward lookup uses the host name (or the FQDN) to find the IP address.
3. A reverse lookup uses the IP address to find host name (or FQDN).
4. A DNS server can forward a DNS request to an upstream DNS server if it cannot resolve a host name to an IP address.
5. An authoritative server is a DNS server that has a full, complete copy of all the records for a particular domain.
6. A caching only DNS server has no zone information; it is not authoritative for any domains.
7. The Root Hints file (also called the Cache.DNS file) lists the 13 root DNS servers. A DNS server uses the Root Hints file to forward a request to a Root DNS server as a last resort to resolve a host name to an IP address.
8. A Root DNS server refers DNS servers to .com or .edu or .gov level DNS servers.
9. Recursion is the process by which a DNS server or host uses root name servers and subsequent servers to perform name resolution. Most client computers do not perform recursion, rather they submit a DNS request to the DNS server and wait for a complete response.