What happens to addresses that do not respond to an IP probe?

The rationale behind assuming that addresses that do not respond to an IP probe are unused stems from the primary intention of network probing. When a network administrator sends out probes to a range of IP addresses, the expectation is to determine which addresses are active and responsive. If a specific address does not reply to the probe, it is often taken to indicate that there is likely no active device or service associated with that IP address.

This assumption allows administrators to efficiently manage their IP address space by identifying addresses that can be reallocated for other uses, informing network design, and optimizing resources. While there are scenarios where non-responsiveness might indicate issues, such as firewalls or other security mechanisms blocking probes, the general practice is to consider those unresponsive addresses as unused unless further investigation determines otherwise.

The other options suggest actions that imply a level of suspicion or concern for security which may not be warranted based solely on a lack of response. Therefore, the response to non-responding IP addresses is typically to categorize them as potentially unused for practical administrative purposes.