In a gray box penetration test, what issue will occur if the client provides nonroutable IP addresses for scanning?

In a gray box penetration test, the situation concerns the use of nonroutable IP addresses, typically referring to private IP addresses as defined by RFC 1918. These addresses are reserved for use within private networks and are not routable on the public internet.

When the client provides these addresses, the penetration testers will not be able to scan them from external sources, such as the internet. This limitation arises because routers on the internet will not forward packets destined for IP addresses in the private address space, rendering external scanning efforts ineffective.

While addressing such issues as IP ranges being too large or overlapping can be relevant to penetration tests, in this specific scenario, the key issue arises solely from the nature of the IP addresses being nonroutable. Consequently, recognizing that the provided IP addresses are RFC 1918 addresses accurately captures why the scanning cannot be performed on them in an external context.

Thus, identifying the presence of RFC 1918 addresses directly relates to the limitations experienced during the gray box penetration test in this context.