Segmentation is a method of isolating system components that store, process, or transmit cardholder data from systems that do not, by using security controls such as firewalls, routers, switches, or other devices1. Segmentation can reduce the scope of the cardholder data environment (CDE) and thus reduce the scope of the PCI DSS assessment, as only the systems and networks within the CDE or connected to the CDE are subject to PCI DSS requirements2. Virtual LANs (VLANs) are one example of such a security control, as they can create logical subnetworks that separate different types of traffic and restrict access between them3. Therefore, the correct answer is option C.

The other options are not true regarding the scenario that describes segmentation of the cardholder data environment (CDE) for the purposes of reducing PCI DSS scope. Option A is not true because routers that monitor network traffic flows between the CDE and out-of-scope networks are not sufficient to isolate the CDE, as they do not prevent or limit the traffic flows. Option B is not true because firewalls that log all network traffic flows between the CDE and out-of-scope networks are not sufficient to isolate the CDE, as they do not block or filter the traffic flows. Option D is not true because a network configuration that prevents all network traffic between the CDE and out-of-scope networks is not realistic or feasible, as some traffic may be necessary for business or legal reasons, such as payment processing, reporting, or auditing. References:

Network Segmentation - PCI Security Standards Council

Guidance for PCI DSS Scoping and Network Segmentation

VLANs and PCI Compliance: What You Need to Know