WAN Security

Correct Answer: Implement QoS for VoIP traffic

The best solution would be to implement QoS (Quality of Service) for VoIP (Voice over Internet Protocol) traffic. QoS is a feature of routers and switches which prioritizes traffic so that more important traffic can pass first, resolving latency issues. This method does not involve disabling encryption (which can risk security), changing the VoIP codec (it's not guaranteed to help as it doesn't deal with network congestion), or enabling QoS for all encrypted traffic (inefficient as not all encrypted traffic is equally important). Hence, focusing QoS on VoIP traffic is the most efficient and effective solution.

Correct Answer: IDS

An Intrusion Detection System (IDS) is the correct choice for monitoring a WAN link for potential security breaches. IDS are designed to detect malicious activities or policy violations in a network. They provide real-time monitoring of network traffic, looking for suspicious activities, which is exactly what a network administrator would need in this case. The other answers are incorrect because they serve different purposes in a network environment. An ASA (Adaptive Security Appliance) is a security device that combines firewall, antivirus, and intrusion prevention capabilities, but it is not specifically designed to monitor a WAN link for potential security breaches. A NAT (Network Address Translation) is used to remap one IP address space into another, helping to improve security and decrease the number of IP addresses an organization needs, but it does not monitor a network for potential breaches. DPI (Deep Packet Inspection) is a type of data processing that inspects in detail the data being sent over a computer network, but it is more about managing network resources and not particularly a tool for security monitoring.

Correct Answer: Implement a firewall

The best solution for the company to protect their network from unauthorized access via their WAN connection is to 'Implement a firewall'. A firewall is a security system that controls incoming and outgoing network traffic based on predetermined security rules. It is a barrier that checks all incoming and outgoing traffic and permits or blocks data packets based on a set of security rules. In comparison, 'Use network segmentation' could be a part of the security strategy, but it would not prevent unauthorized access on its own. 'Upgrade the WAN link's bandwidth' would not affect network security and could even make the network more attractive to attackers. 'Disable remote access' could be too restrictive and not practical for businesses that require remote work or have multiple locations. Thus, the best solution is 'Implement a firewall'.