8.1 DNS Services

Question 1

DOMAI§N NAME

Answer 1

In data networks, devices are labeled with numeric IP addresses to send and receive data over networks. Domain names were created to convert the numeric address into a simple, recognizable name.

Question 2

FQDNs

Answer 2

Fully-Qualified Domain Names

Question 3

DNS

Answer 3

Domain Name System

The DNS protocol defines an automated service that matches resource names with the required numeric network address.
It includes the format for queries, responses, and data.
The DNS protocol communications use a single format called a message.
This message format is used for all types of client queries and server responses, error messages, and the transfer of resource record information between servers.

Question 4

DNS SERVER

Answer 4

The DNS server stores different types of resource records that are used to resolve names.
These records contain the name, address, and type of record.
Some of these record types are as follows:

A - An end device IPv4 address
NS - An authoritative name server
AAAA - An end device IPv6 address (pronounced quad-A)
MX - A mail exchange record

Question 5

ipconfig /displaydns

Answer 5

The DNS client service on Windows PCs also stores previously resolved names in memory.
The ipconfig /displaydns command displays all of the cached DNS entries.

Answer 6

DNS uses the same message format between servers, consisting of a question, answer, authority, and additional information for all types of client queries and server responses, error messages, and transfer of resource record information.

Question 7

DNS HIERARCHY

Answer 7

The DNS protocol uses a hierarchical system to create a database to provide name resolution, as shown in the figure. DNS uses domain names to form the hierarchy.

The naming structure is broken down into small, manageable zones. Each DNS server maintains a specific database file and is only responsible for managing name-to-IP mappings for that small portion of the entire DNS structure. When a DNS server receives a request for a name translation that is not within its DNS zone, the DNS server forwards the request to another DNS server within the proper zone for translation. DNS is scalable because hostname resolution is spread across multiple servers.

The different top-level domains represent either the type of organization or the country of origin. Examples of top-level domains are the following:

.com - a business or industry
.org - a non-profit organization
.au - Australia
.co - Colombia

The figure shows the DNS Hierachy tree. At the top is the Root Level Domain with the TOp-Level Domains(TLD) connected undererneath the Root Level Domainmain.
THe TLDs are .net, .edu, .com,.au, .co, and other top-level doamins.
Under the .com TLD is the Second Level domain www.cisco.com and under cisco.com are www.cisco.com , ftp.cisco.com, and mail.cisco.com.

Question 8

nslookup

Answer 8

By issuing the nslookup command, the default DNS server that is configured is displayed.

Computer operating systems also have a utility called nslookup that allows the user to manually query the name servers to resolve a given host name. This utility can also be used to troubleshoot name resolution issues and to verify the current status of the name servers.

When the nslookup command is issued, the default DNS server configured for your host is displayed. The name of a host or domain can be entered at the nslookup prompt. The nslookup utility has many options available for extensive testing and verification of the DNS process.