A Secure Sockets Layer (SSL) virtual private network (VPN) would provide the network administrator who requires remote access a secure and reliable method of accessing the system over the Internet. Security Assertion Markup Language (SAML) standards for federation will provide cross-web service authentication and authorization.
Incorrect Answers:
A: Blocking the application would prevent the network administrator who requires remote access from accessing the system. While this will address the presence of the unauthorized remote access application, it will not address the network administrator's need for remote access.
B: Installing the unauthorized remote access application on the rest of the servers would not be an "appropriate" solution. An appropriate solution would provide a secure form of remote access to the network administrator who requires remote access.
D: An access control list (ACL) is used for packer filtering and for selecting types of traffic to be analyzed, forwarded, or blocked by the firewall or device. The ACL may block traffic based on source and destination address, interface, port, protocol, thresholds and various other criteria. However, network address translation (NAT) is not used for remote access. It is used to map private IPv4 addresses to a single public IPv4 address, allowing multiple internal hosts with private IPv4 addresses to access the internet via the public IPv4 address.
References:
BOOK pp. 28, 40-41, 110-112, 138. 335-336
https://en.wikipedia.org/wiki/Network_address_translation