ns3-bgp-netgen-ng is the successor of ns3-bgp-netgen. ns3-bgp-netgen-ng use JSON-based configuration to generate ns3 script. JSON schema for the configuration is available here.
ns3-bgp-netgen-ng has a web-based UI that allows the user to generate BGP networks with a few clicks. One could also choose to write the configuration by hand if they want to.
ns3-bgp-netgen-ng has added process-based multi-instance support that allows the user to speed up the simulation by running multiple ns3 instances with each instance running only a part of the simulated network. You will notice that now every network and router in configuration file has an instance_id associated with them, indicating which ns3 instance that the router or network should be running on.
Routers/Network with the same instance_id will be put into the same process. A process will be created for every instance_id. Routers can have devices that connect to a network or peer in a different instance. When this happens, a UNIX socket pair will be created (with socketpair(2)) to handle communication between different instances.
MIT