Ping sweeping is a technique used in network reconnaissance to identify which IP addresses in a range are active or live. By sending ICMP echo requests ("ping") to multiple hosts and observing which ones respond, an attacker or, in this case, a red team member like Allan, can determine which systems are up and potentially vulnerable to further exploration or attack. This method is foundational for mapping the network before deploying more targeted exploits or scans.
References:EC-Council's Certified Incident Handler (CREST CPTIA) program discusses various reconnaissance techniques, including ping sweeping, as a preliminary step in network analysis and vulnerability assessment.