In which scenario will an administrator need to manually define Proxy ARP?

Proxy ARP is a technique that allows a device to respond to ARP requests on behalf of another IP address. Proxy ARP is required for Manual Static NAT when the translated IP address does not belong to one of the firewall’s interfaces. This is because the firewall needs to intercept the packets destined to the translated IP address and forward them to the original IP address after applying the NAT rule. Without Proxy ARP, the packets would not reach the firewall and the NAT would not work. Proxy ARP is not required for Automatic Static NAT or Automatic Hide NAT, because these types of NAT use IP addresses that belong to the firewall’s interfaces. Proxy ARP is also not required for Manual Hide NAT, because this type of NAT does not change the destination IP address of the packets, only the source IP address. References: Check Point R81 Security Management Administration Guide, page 115