Your network contains an Active Directory domainnamed contoso.com.
You plan to deploy a child domain named sales.contoso.com.
The domain controllersin sales.contoso.comwill be DNS servers for sales.contoso.com.
You need to ensure that users in contoso.com can connect to servers in sales.contoso.com by using
fully qualified domain names (FQDNs).
What should you do?

A.
Create a DNS forwarder.

B.
Create a DNS delegation.

C.
Configure root hint servers.

D.
Configure an alternate DNS server on all client computers.

Explanation:
http://technet.microsoft.com/en-us/library/cc784494%28v=ws.10%29.aspx
Delegating zones
DNS provides the option of dividing up the namespace into one or more zones, which can then be stored,
distributed, and replicated to other DNS servers. When deciding whether to divide your DNS namespace to
make additional zones, consider the following reasons to use additional zones:
A need to delegate management of part of your DNS namespace to another location or department within
your organization.
A need to divide one large zone into smaller zones for distributing traffic loads among multiple servers,
improve DNS name resolution performance, or create a more fault-tolerant DNS environment.
A need to extend the namespace by adding numerous subdomains at once, such as to accommodate the
opening of a new branch or site.
If, for any of these reasons, you could benefit from delegating zones, it might make sense to restructure your
namespace by adding additional zones. When choosinghow to structure zones, you should use a plan that
reflects the structure of your organization.
When delegating zones within your namespace, be aware that for each new zone you create, you will need
delegation records in other zones that point to theauthoritative DNS servers for the new zone. This is
necessary both to transfer authority and to providecorrect referral to other DNS servers and clients of the new
servers being made authoritative for the new zone.
When a standard primary zone is first created, it is stored as a text file containing all resource record
information on a single DNS server. This server acts as the primary master for the zone. Zone information can
be replicated to other DNS servers to improve faulttolerance and server performance.
When structuring your zones, there are several goodreasons to use additional DNS servers for zone
replication:
1. Added DNS servers provide zone redundancy, enabling DNS names in the zone to be resolved for clients
if a primary server for the zone stops responding.
2. Added DNS servers can be placed so as to reduce DNS network traffic. For example, adding a DNS
server to the opposing side of a low-speed WAN linkcan be useful in managing and reducing network
traffic.
3. Additional secondary servers can be used to reduce loads on a primary server for a zone.
Example: Delegating a subdomain to a new zone
As shown in the following figure, when a new zone for a subdomain (example.microsoft.com) is created,
delegation from the parent zone (microsoft.com) is needed.

In this example, an authoritative DNS server computer for the newly delegated example.microsoft.com
subdomain is named based on a derivative subdomain included in the new zone (ns1.us.example.microsoft.
com). To make this server known to others outside of the new delegated zone, two RRs are needed in the
microsoft.com zone to complete delegation to the new zone.
These RRs include:
An NS RR to effect the delegation. This RR is used to advertise that the server named ns1.us.example.
microsoft.com is an authoritative server for the delegated subdomain.
An A RR (also known as a glue record) is neededto resolve the name of the server specified in theNS
RR to its IP address. The process of resolving the host name in this RR to the delegated DNS server inthe
NS RR is sometimes referred to as glue chasing.
Note
When zone delegations are correctly configured,normal zone referral behavior can sometimes be
circumvented if you are using forwarders in your DNS server configuration.