Chapter 2 Configuring and Troubleshooting DNS

2.1 Installing the DNS Server Role
 Overview of the Domain Name System Role
 Overview of the DNS Namespace
 DNS Improvements for Windows Server 2008
 Considerations for Deploying the DNS Server Role
Overview of the Domain Name System
 Domain Name System (DNS) is a name-resolution service that
resolves names to numbers
DNS is a hierarchical distributed database, this means that the
database is separated logically, allowing many different servers to
host the worldwide database of DNS names
DNS is a system for naming computers and network services that
is organized into a hierarchy of domains
DNS is the foundation of the Internet naming scheme
DNS supports accessing resources by using alphanumeric names
InterNIC & MyNIC are responsible for managing the domain
DNS was created to support the Internet’s growing number of
Overview of the DNS Namespace
 The DNS Namespace facilitates how a DNS client
locates a computer
 It is organized hierarchically or in layers to distribute
information across many servers
DNS Improvements for Windows Server
 New or enhanced features in the Windows Server 2008
version of DNS include:
Background zone loading
IP version 6 support
Support for read-only domain controller
Global single names
Considerations for Deploying the DNS
Server Role
 The DNS Server role is critical in the configuration of
Active Directory and Windows Network infrastructure
When planning to deploy DNS, there are several
considerations that need to be reviewed:
Server capacity planning
Where to place DNS servers
Service availability
2.2 Configuring the DNS Server
 What are the components of a DNS solutions
 DNS Resource Records
 What are Root Hints
 What is a DNS Query
 What are Recursive Queries
 What are Iterative Queries
 What is a Forwarder
 What is Conditional Forwarding
 How DNS Sever Caching works
What are the components of a DNS
 The components of a DNS solution include DNS
servers, DNS servers on the Internet, and DNS clients
DNS Resource Records
 DNS resource records include :
- SOA: Start of Authority
- A: Host record
- CNAME: Alias record
- MX: Mail Exchange record
- SRV: Service resources
- NS: Name Servers
- AAAA: IPv6 DNS record
What are Root Hints
 Root Hints contain the IP addresses for DNS root
 Root Hints are the list of 13 servers on the Internet that
the Internet Assigned Numbers Authority (IANA)
maintains and that the DNS server uses if it cannot
resolve a DNS query by using DNS forwarder or its
own cache
 The Root Hints are the highest servers in the DNS
hierarchy and can provide the necessary information
for a DNS server to perform an iterative query to the
next lowest layer of the DNS namespace
What is a DNS Query
 A query is a request for name resolution and is directed to a DNS
Queries are recursive or iterative
DNS clients and DNS servers both initiate queries
DNS servers are authoritative or nonauthoritative for a
An authoritative DNS server for the namespace will either:
Return the requested IP address
Return an authoritative “No”
A nonauthoritative DNS server for the namespace will either:
Check its cache
Use forwarders
Use root hints
What are Recursive Queries
 A recursive query is sent to a DNS server and requires a
complete answer
A recursive query can have 2 possible results:
It returns the IP address of the host requested
The DNS server cannot resolve an address
For security reasons, it sometimes is necessary to
disable recursive queries on a DNS server
What are Iterative Queries
 An iterative query directed to a DNS server may be
answered with a referral to another DNS server
 Iterative queries provide a mechanism for accessing
domain name information that resides across the DNS
system, and enable servers to quickly and efficiently
resolve names across many servers
What is a Forwarder
 A forwarder is a DNS server designated to resolve
external or offsite DNS domain names
 A forwarder is a network DNS server that forwards
DNS queries for external DNS names to DNS servers
outside that network
What is Conditional Forwarding
 Conditional forwarding forwards requests using a
domain name condition
 Conditional forwarding forwarder is a DNS server on a
network that forwards DNS queries according to the
query’s DNS domain name
How DNS Server Caching works
 DNS caching increases the performance of the
organization’s DNS system by decreasing the time it
takes to provide DNS lookups
 When a DNS server resolves a DNS name successfully,
it adds the name to its cache
 Over time, this builds a cache of domain names and
their associates IP addresses for the most common
domains that the organization uses or accesses
2.3 Configuring DNS Zones
 What is a DNS Zone
 What are the DNS Zone types
 What are Forward and Reverse Lookup Zones
 What are Stub Zones
 DNS Zone Delegation
What is a DNS Zone
 A DNS zone hosts all or a portion of a domain and its
What are the DNS Zone Types
Read/write copy of a DNS database
Read-only copy of a DNS database
Copy of a zone that contains only
records used to locate name servers
Active Directory integrated
Zone data is stored in Active Directory
rather than in zone files
What are Forward and Reverse Lookup
 The forward lookup zone resolves host names to IP
addresses and hosts the common resources records: A,
 The reverse lookup zone resolves an IP address to a
domain name and hosts SOA, NS and PTR records
What are Stub Zones
 A stub zone is a copy of a zone that contains only those
resource records necessary to identify that zone’s
authoritative DNS servers
 A stub zone resolves names between separate DNS
namespaces, which may be necessary when a corporate
merger requires that the DNS servers for 2 separate
DNS namespaces resolve names for clients in both
DNS Zone Delegation
 DNS is a hierarchical system and zone delegation
connects the DNS layers together
 A zone delegation points to the next hierarchical level
down and identifies the name servers responsible for
lower-level domain
2.4 Configuring DNS Zone Transfer
 What is a DNS Zone Transfer
 How DNS Notify works
 Securing Zone Transfers
What is a DNS Zone Transfer
 A DNS zone transfer is the synchronization of
authoritative DNS zone data between DNS servers
 A zone transfer occur when you transfer the DNS zone
that is on one server to another DNS server
 Zone transfer synchronize primary and secondary DNS
server zones.
 Discrepancies in primary and secondary zones can
cause service outages and host names that are resolved
How DNS Notify works
 A DNS notify is an update to the original DNS protocol
specification that permits notification to secondary
servers when zone changes occur
 This is useful in a time-sensitive environment, where
data accuracy is important
Securing Zone Transfers
 Zone information provides organizational data, so you
should take precautions to ensure it is secure from
malicious access and that it cannot be overwritten with
bad data (known as DNS poisoning)
 One way in which you can protect the DNS
infrastructure is to secure the zone transfers and use
secure dynamic updates
2.5 Managing and Troubleshooting
 What is Time to Live, Aging and Scavenging
 Demonstration: Managing DNS Records
 Testing the DNS server configuration
 Tools that identify problems with DNS
 Monitoring DNS using the DNS Event Log and Debug
What is Time to Live, Aging and
Time to Live (TTL)
Indicates how long a DNS record will
remain valid
Occurs when records that have been
inserted into the DNS server reach their
expiration and are removed
Performs DNS server resource record
grooming for old records in DNS
Testing the DNS Server Configuration
 You can test the DNS server configuration by using:
- A simple query to ensure that the DNS service is
- A recursive query to ensure that the DNS server can
communicate with the upstream DNS service
Tools that Identify Problems with DNS
 Issues can occur when you do not configure the DNS server
and its zones and resource records properly
 When resource records are causing issues, it can sometimes
be more difficult to identify the issue because
configuration problems are not always obvious
Used to:
Troubleshoot DNS problems
Edit the DNS configuration
Diagnose common DNS
Monitoring DNS using the DNS Event
Log and Debug Logging
 Monitor DNS events in the event log to:
- Monitor zone transfer information
- Monitor computer events
 Enable DNS debug logging to view granular verbose
information about DNS activities
End of Chapter 2

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