0Which of the following options would you choose to provide a fault-tolerant DHCP infrastructure for the company that supports the client computers on the internal network?

You are an Enterprise administrator for contoso.com. The corporate network of the company consists of a single Active Directory domain.

The network contains two DHCP servers called contosoDHCP1 and contosoDHCP2 and 500 DHCP client computers that are located on a single subnet. A router that has a single IP address on the internal interface separates the internal network from the Internet.

contosoDHCP1 server is configured with:
Starting IP address: 172.16.0.1
Ending IP address: 172.16.3.254
Subnet mask: 255.255.248.0

Which of the following options would you choose to provide a fault-tolerant DHCP infrastructure for the company that supports the client computers on the internal network? You need to configure DHCP2 to ensure that all client computers must be able to obtain a valid IP address if a DHCP server fails.

A.
Create a scope for the subnet 172.17.0.0/16. Configure the scope to use a starting IP address of 172.17.0.1 and an ending IP address of 172.17.255.254.

B.
Create a scope for the subnet 172.16.0.0/20. Configure the scope to use a starting IP address of 172.16.0.1 and an ending IP address of 172.16.15.254.

C.
Create a scope for the subnet 172.16.0.0/20. Configure the scope to use a starting IP address of 172.16.8.1 and an ending IP address of 172.16.15.254.

D.
Create a scope for the subnet 172.16.0.0/21. Configure the scope to use a starting IP address of 172.16.4.1 and an ending IP address of 172.16.7.254.

E.
None of the above

Explanation:

The subnet mask 255.255.248.0 means a /21 subnet. For load balancing you need to ensure that the DHCP2 should be configured on the same network therefore, you need to select answer D where the subnet is 172.16.0.0/21.

The /21 network can contain IP address range from 172.16.0.1 to 172.16.7.255, which means 2048 total hosts can be configured. DHCP1 already contains the IP address range from 172.16.0.1 to 172.16.3.254 to serve 500 hosts.

In case of the failure of DHCP1, another IP address range is required for the 500 computers that the network has. Therefore DHCP2 can contain the range of 172.16.4.1 to 172.16.7.254

Reference: Subnet Addressing
http://www.networkcomputing.com/unixworld/tutorial/001.html

Reference: Effects of Subnetting a Class B Network http://www.weird.com/~woods/classb.html