A reservation is a feature of DHCP that allows a device with a specific MAC address to be always assigned the same IP address from the DHCP server. A reservation is configured by mapping the MAC address of the device to the desired IP address on the DHCP server. This ensures that the device will always receive the same IP address, regardless of the lease time or the availability of other IP addresses in the DHCP pool. The other options are not features of DHCP that can ensure a device with a specific MAC address is always assigned the same IP address, as they either do not involve MAC addresses, do not guarantee IP address consistency, or do not use DHCP at all. References: CISSP - Certified Information Systems Security Professional, Domain 4.
Communication and Network Security, 4.2 Secure network components, 4.2.1 Establish secure communication channels, 4.2.1.1 Transmission methods; CISSP Exam Outline, Domain 4. Communication and Network Security, 4.2 Secure network components, 4.2.1 Establish secure communication channels,
4.2.1.1 Transmission methods

Personnel cause more security issues than hacker attacks, outside espionage, or
equipment failure.
The following answers are incorrect because:
Outside espionage is incorrect as it is not the best answer.
Hackers is also incorrect as it is not the best answer.
Equipment failure is also incorrect as it is not the best answer.
Reference : Shon Harris AIO v3 , Chapter-3: Security Management Practices , Page : 56

According to CISSP documentation, the actual definition and procedures defined inside an organization disaster recovery policy are of private nature. Only people working in the company and with a role inside it should know about those procedures. Its not a good practice to be divulgating Disaster recovery procedures to external people.
Many times external people need to know who is involved in it, and who is responsible.
This could be the case of a vendor providing replacement equipment in case of disaster.

Section: Security Architecture and Engineering

The correct answer is "Replaces older Frame Relay-switched networks". TACACS+ has nothing to do with Frame Relay networks.