After this lesson, you will be able to
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Identify the various components of a DNS infrastructure. Describe the various DNS server types and their functions in an existing infrastructure. Identify the current namespace.
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Estimated lesson time: 20 minutes
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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 1, this name resolution process can be quite involved. In this section, you will look at the various components that make it all happen.
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Components of DNS
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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.
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Designing a DNS Structure
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The ability to recognize the components of a DNS infrastructure begins with knowing and understanding how DNS functions. DNS is a database. Like any database, it keeps track of records or, more specifically, resource records. Table 6-1 shows some of the more popular resource record types a DNS server may store in a zone.
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DNS Resource Records
Description Contained in the beginning of every zone Indicates that the server is authoritative for the zone Maps the FQDN (Fully Qualified Domain Name) to an IP address Maps an IP address to an FQDN Creates an alias name for an FQDN Specifies a mail exchange server that processes or forwards mail for a particular DNS domain Specifies the location of the servers that perform a specific ser vice, such as mail servers, domain controllers, Web servers, etc.
Record Type SOA (Start of Authority) NS (Name Server) A (host) PTR (Pointer Record) CNAME (Canonical name) MX (Mail Exchange) SRV (Service)
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. 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.
Analyzing the Existing DNS Implementation
DNS Server Primary Zone DNS Server Secondary Zone
DNS Server Active Directory Integrated Zone DNS Server Active Directory Integrated Zone
DNS Server Active Directory Integrated Primary Zone
DNS Server Active Directory Integrated Stub Zone
You can choose between several different zone types.
Configuring zones will be covered later in the chapter. For now, you want to be able to recognize how the current DNS infrastructure is configured for documentation pur poses only.
Having only one DNS server on a network holding all of the resource records would not be prudent. There must be a method to replicate this important data to other DNS servers. Zone transfers may occur three different ways in Windows Server 2003:
Incremental Zone Transfer (IXFR) In an incremental zone transfer (IXFR), servers keep track of, and transfer only, changes that are made to resource records in a particular zone, the advantage being that less traffic is sent over the network. Full Zone Transfer (AXFR) In this type of zone transfer, a response to a DNS query will transfer the entire zone to the secondary DNS server. This type of zone transfer across a slow wide area network (WAN) link can be problematic, so it is important to document which type of zone transfer is occurring on the network. Fast zone transfer Fast zone transfer allows more than one resource record to be transferred in a message as it replicates from one DNS server to another. This is the default zone transfer methodology for Windows Server 2003.
Later, you will design your DNS infrastructure based on the topology of your network. For now, you should be able to look at the current system and determine how it is configured.