Pass4sure Cisco 642-642 exam information
Analyzing the Existing DNS Implementation 350-001 156-915.65 642-642
Unless you are tasked with building a network infrastructure from the ground up, most
network administrators have to understand and work with DNS infrastructures that are
already in place. This lesson includes an overview of the DNS components and discusses
some of the terminology you will need to understand before you can design
and implement a DNS strategy for your company.
The first step in analyzing a company’s network infrastructure is to perform an analysis
of the company itself. As discussed in Chapter 2, understanding how a company works
and how its information flows lays a critical foundation for the rest of your network
design. In this lesson, you learn to gather information regarding the DNS infrastructure
that is in place.
DNS Overview
Most human beings do not like working with numbers or having to memorize Internet
Protocol (IP) addresses to connect to a resource on the network. It’s a lot easier to
memorize www.microsoft.com as an address than 172.16.45.67. When a Fully Qualified
Domain Name (FQDN) such as www.microsoft.com is entered by a user on a network,
there must be a method or component that takes that name and resolves it to an IP
number. DNS does exactly that. As you saw in Chapter 1, this name resolution process
can be quite involved. In this section, you will look at the various components that
make it all happen.
Components of DNS
Because you have already gathered all of the information pertaining to the physical
locations of the various departments and divisions of your company, and have created
network diagrams of the present infrastructure, you are almost ready to analyze the
DNS structure of the company. The diagrams you have created illustrate where all
servers, routers, switches, and so on are located. This information, combined with the
locations and total amount of hosts, subnets, and routers, will help you to understand
how the present DNS infrastructure is configured.
DNS Zones
A zone is defined as a contiguous portion of a DNS tree that is administered as a
separate entity by a DNS server. It can store information about one or more domains.
A zone contains resource records associated with a particular domain. For example,
Contoso’s DNS namespace for the domain contoso.com may have originally been
configured as a single zone, but as the domain grows and many subdomains are
added—such as ftp.contoso.com, www.contoso.com, marketing.contoso.com, and so
on—you can assign different zones to each subdomain.
Windows Server 2003 allows you to choose between several different zone types (as
shown in Figure 6-1).
Primary zone Contains a local copy of the DNS zone where resource records
are created and updated. VCP-310 640-802 190-848
Secondary zone A read-only copy of a DNS zone. It can be updated only through
replication from a primary zone, and is used for redundancy and load balancing.
Active Directory integrated zone A primary zone stored in Active Directory.
Stub zone A copy of a zone that contains only the resource records needed to
identify authoritative DNS servers, thereby simplifying DNS administration and
improving name resolution.