Which configuration is likely to isolate a DHCP server to its own subnet?

Isolating a DHCP server to its own subnet can be effectively achieved through the appropriate configuration of VLANs. Virtual Local Area Networks (VLANs) segment a network into distinct broadcast domains, allowing different subnets to communicate while controlling traffic flow between them. By placing the DHCP server in its dedicated VLAN, it becomes a separate broadcast domain that limits the scope of DHCP broadcasts, effectively isolating it from other subnets.

This configuration enhances network security and performance by ensuring that the DHCP server serves only the devices within its designated VLAN. Only clients that are part of that VLAN can receive DHCP leases, preventing unauthorized devices on other VLANs from accessing DHCP services.

In contrast, the other options do not provide the same level of effective isolation for a DHCP server within its own subnet. Access control lists (ACLs) can control access to a device, but they don't segment traffic or create a separate broadcast domain like VLANs do. Implementing a VPN creates a secure connection over the internet but does not pertain to subnet isolation in a local network context. Disabling multicast does not directly lead to isolating a DHCP server but can impact the functioning of DHCP as it relies on certain multicast messages for service discovery.