The default configuration of Peplink WAN interfaces makes use of NAT. IP forwarding mode disables NAT on interface for standard routing.
Reasons to use IP forwarding:
- Keep existing topology, subnets, and routing when replacing router in existing network. As opposed to Drop-In mode where router is added to existing network in between devices.
- Save work of one-to-one NAT mapping. Use those IPs on the LAN directly.
- Real source IPs should be visible.
- All LAN side hosts full accessible from WAN.
- Conservation of public IP address space.
- Connect unroutable IP address to public internet.