No forwarding rules would be necessary as both devices would ring.

However, NAT loopback makes the router lookup the destination address and port in its port forwarding rules table.

The router receives the traffic and makes forwarding decisions based on a set of forwarding rules, typically a QoS policy or a set of filters.

The 1905 ALME provides a list of primitives to manage forwarding rules per flow (Get, Set, Modify and Remove).

NAT Passthrough: the ability to connect to the server behind a NAT without configuring the router's port forwarding rules.

Likewise, upon receiving a labelled packet which is destined to exit the MPLS domain, the LER strips off the label and forwards the resulting IP packet using normal IP forwarding rules.