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Exchange Server 2010 : Examining DNS Components (part 1) - DNS Zones & DNS Queries

3/20/2011 8:53:00 AM
As previously mentioned, name servers, or DNS servers, are systems that store information about the domain namespace. Name servers can have either the entire domain namespace or just a portion of the namespace. When a name server only has a part of the domain namespace, the portion of the namespace is called a zone.

DNS Zones

There is a subtle difference between zones and domains. All top-level domains, and many domains at the second and lower levels, are broken into zones—smaller, more manageable units by delegation. A zone is the primary delegation mechanism in DNS over which a particular server can resolve requests. Any server that hosts a zone is said to be authoritative for that zone, with the exception of stub zones.

A name server can have authority over more than one zone. Different portions of the DNS namespace can be divided into zones, each of which can be hosted on a DNS server or group of servers.

Forward Lookup Zones

A forward lookup zone is created to do forward lookups on the DNS database, resolving names to IP addresses and resource information.

Reverse Lookup Zones

A reverse lookup zone performs the opposite operation as the forward lookup zone. IP addresses are matched up with a common name in a reverse lookup zone. This is similar to knowing the phone number but not knowing the name associated with it. Reverse lookup zones must be manually created, and do not exist in every implementation. Reverse lookup zones are primarily populated with PTR records, which serve to point the reverse lookup query to the appropriate name.

Tip

It is good practice for the Simple Mail Transfer Protocol (SMTP) mail server to have a record in the reverse lookup zone. Spam control sites check for the existence of this record. It is possible to be placed on a spammer list if the site does not have a PTR record for the MX entry in the DNS reverse lookup zone.


Active Directory–Integrated Zones

A Windows 2003 or Windows 2008 DNS server can store zone information in two distinct formats: Active Directory–integrated or standard text file. An Active Directory–integrated zone is an available option when the DNS server is installed on an Active Directory domain controller. When a DNS zone is installed as an Active Directory zone, the DNS information is automatically updated on other server AD domain controllers with DNS by using Active Directory’s multimaster update techniques. Zone information stored in the Active Directory allows DNS zone transfers to be part of the Active Directory replication process secured by Kerberos authentication.

Primary Zones

In traditional (non-Active Directory–integrated) DNS, a single server serves as the master DNS server for a zone, and all changes made to that particular zone are done on that particular server. A single DNS server can host multiple zones, and can be primary for one and secondary for another. If a zone is primary, however, all requested changes for that particular zone must be done on the server that holds the master copy of the zone. As illustrated in Figure 1, companyabc.com is set up on DC1 as an Active Directory–integrated primary zone. However, DC1 also holds a secondary zone copy of the amaris.org zone.

Figure 1. DNS primary and secondary zones.

Creating a new primary zone manually is a fairly straightforward process. The following procedure outlines the creation of a standard zone for the companyabc.com DNS namespace:

1.
Open the Server Manager.

2.
Navigate to Roles\DNS Server\DNS\<Servername>\Forward Lookup Zones.

3.
Right-click Forward Lookup Zones, and choose New Zone.

4.
Click Next on the welcome screen.

5.
Select Primary Zone from the list of zone types available. Also, determine if the zone will be stored in Active Directory. If not, uncheck the Store the Zone in Active Directory check box. Click Next to continue.

6.
If the zone is Active Directory–integrated, the replication scope needs to be selected. The replication can be to all DNS servers in the forest, all DNS servers in the domain, or just to the domain controllers in the domain for Windows 2000 compatibility.

7.
Type the name of the primary zone to be created, and click Next.

8.
Determine whether dynamic updates will be allowed in this zone. By default, Allow Only Secure Dynamic Updates is selected. Click Next to continue.

9.
Click Finish on the Summary page to create the zone.

Secondary Zones

A secondary zone is established to provide redundancy and load balancing for the primary zone. Secondary zones are not necessary if the zone has been set up as the Active Directory–integrated zone because the zone will be replicated to all domain controllers in the domain. With secondary zones, each copy of the DNS zone database is read-only, however, because all recordkeeping is done on the primary zone copy. A single DNS server can contain several zones that are primary and several that are secondary. The zone creation process is similar to the one outlined in the preceding section on primary zones, but with the difference being that the zone is transferred from an existing primary server.

Stub Zones (Delegated Zones)

A stub zone is a zone that contains no information about the members in a domain but simply serves to forward queries to a list of designated name servers for different domains. A stub zone contains only NS, SOA, and glue records. Glue records are A records that work in conjunction with a particular NS record to resolve the IP address of a particular name server. A server that hosts a stub zone for a namespace is not authoritative for that zone.

A stub zone effectively serves as a placeholder for a zone that is authoritative on another server. It allows a server to forward queries that are made to a specific zone to the list of name servers in that zone.

DNS Queries

The primary function of DNS is to provide name resolution for requesting clients, so the query mechanism is one of the most important elements in the system. Two types of queries are commonly made to a DNS database: recursive and iterative.

Recursive Queries

Recursive queries are most often performed by resolvers, or clients that need to have a specific name resolved by a DNS server. Recursive queries are also accomplished by a DNS server if forwarders are configured to be used on a particular name server. A recursive query asks whether a particular record can be resolved by a particular name server. The response to a recursive query is either negative or positive.

Iterative Queries

Iterative queries ask a DNS server to either resolve the query or make a best-guess referral to a DNS server that might contain more accurate information about where the query can be resolved. Another iterative query is then performed to the referred server and so on until a result, positive or negative, is obtained.

Other -----------------
- Domain Name System and Its Role in Exchange Server 2010
- Configuring Windows Server 2003 for LAN Routing (part 4) - Exploring LAN Routing Scenarios
- Configuring Windows Server 2003 for LAN Routing (part 3) - Managing General IP Routing Properties & Working with Routing Tables
- Configuring Windows Server 2003 for LAN Routing (part 2) - Configuring Routing And Remote Access Service Properties
- Configuring Windows Server 2003 for LAN Routing (part 1) - Using the Routing And Remote Access Console
- Microsoft Content Management Server : Managing Template Galleries and Templates (part 4) - Moving Template Galleries and Templates
- Microsoft Content Management Server : Managing Template Galleries and Templates (part 3) - Copying Templates
- Microsoft Content Management Server : Managing Template Galleries and Templates (part 2) - Creating Templates
- Microsoft Content Management Server : Managing Template Galleries and Templates (part 1) - Creating Template Galleries
- Integrating Exchange Server 2010 in a Non-Windows Environment : Administrative Improvements with Windows Server 2008
 
 
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