Your network contains an Active Directory domain named contoso.com.
The Active Directory sites are configured as shown in the Sites exhibit. (Click the Exhibit
button.)

You need to ensure that DC1 and DC4 are the only servers that replicate Active Directory
changes between the sites.
What should you do?

A.
Configure DC1 as a preferred bridgehead server for IP transport.

B.
Configure DC4 as a preferred bridgehead server for IP transport.

C.
From the DC4 server object, create a Connection object for DC1.

D.
From the DC1 server object, create a Connection object for DC4.

Explanation:

MCTS 70-640 Cert Guide: Windows Server 2008 Active Directory, Configuring (Pearson IT
Certification, 2010) pages 193, 194
Bridgehead Servers
A bridgehead server is the domain controller designated by each site’s KCC to take control
of intersite replication. The bridgehead server receives information replicated from other
sites and replicates it to its site’s other domain controllers. It ensures that the greatest
portion of replication occurs within sites rather than between them.
In most cases, the KCC automatically decides which domain controller acts as the
bridgehead server.
However, you can use Active Directory Sites and Services to specify which domain controller
will be the preferred bridgehead server by using the following steps:
1. In Active Directory Sites and Services, expand the site in which you want to specify the
preferred bridgehead server.
2. Expand the Servers folder to locate the desired server, right-click it, and then choose
Properties.
3. From the list labeled Transports available for intersite data transfer, select the protocol(s)
for which you want to designate this server as a preferred bridgehead server and then click
Add.
Original explanation:
Please Check Answer
Connections. The KCC creates connections that enable domain controllers to replicate with
each other. A connection defines a one-way, inbound route from one domain controller, the
source, to another domain controller, the destination. The KCC reuses existing connections
where it can, deletes unused connections, and creates new connections if none exist that
meet the current need. Bridgehead Servers. To communicate across site links, the KCC
automatically designates a single server, called the bridgehead server, in each site to
perform site-to-site replication. Subsequent replication occurs by replication within a site.
When site links are established, authorized administrators can designate the bridgehead
servers that they want to receive replication between sites. By designating a specific server
to receive replication between sites, rather than using any available server, authorized
administrators can specify the most beneficial conditions for the connection between sites.
Bridgehead servers ensure that most replication occurs within sites rather than between
sites.
http://technet.microsoft.com/library/dd277429.aspx