In an NC2 environment using Flow Virtual Networking (FVN), routing traffic between the AWS cloud and on-premises environments requires specific configuration of the Transit VPC and User VPCs.
To ensure that traffic reaching the on-premises environment is not subjected to Network Address Translation (NAT)-which would obscure the original IP addresses and potentially break connectivity for certain applications-the routing tables must point to the correct internal gateway interface. Theoverlay-external- subnet-nonatacts as the designated gateway for traffic that should be routed without address translation.
Verifying that the " Next Hop " for on-premises prefixes is set to this specific subnet ensures that internal communication remains transparent and complies with standard corporate networking and security policies.