The symptoms point to a rogue DHCP scenario, which CEH materials commonly describe as a method attackers use to disrupt networks or perform man-in-the-middle attacks. If an unauthorized device begins answering DHCP requests faster than the legitimate DHCP server, endpoints may receive incorrect IP settings such as a fake default gateway or DNS server. This causes loss of connectivity to internal applications like a CRM system and can silently redirect traffic through an attacker-controlled host. The question explicitly mentions "irregular IP assignment attempts" tied to an unfamiliar device, which aligns strongly with rogue DHCP behavior rather than ARP-only manipulation or simple MAC-limit violations.
DHCP snooping is a Layer 2 security feature on Cisco switches that filters untrusted DHCP messages and allows only authorized DHCP servers on trusted ports. When enabled for the affected VLAN, the switch will drop DHCP offers and acknowledgments arriving on untrusted access ports, stopping the rogue device from leasing addresses. Option A, ip dhcp snooping vlan 10, is the command that applies DHCP snooping protection to the specific VLAN experiencing the issue, which matches the "subnet logs" and the localized impact described.
Option B, Dynamic ARP Inspection, primarily mitigates ARP spoofing and relies on DHCP snooping bindings, but it does not directly stop rogue DHCP leasing. Option D, port security, can limit MAC addresses but does not specifically block DHCP server behavior. Option C enables the feature globally but does not target the VLAN; the VLAN-specific activation in A best matches the scenario and the immediate restoration of correct addressing and connectivity.